The Big One

The Big One,
by Osterholm and Olshaker.

I’ve been reading The Big One: How We Must Prepare For Future Deadly Pandemics, by Michael Osterholm and Mark Olshaker. As is my wont, while I read I watched for physics applied to biology and medicine. And sure enough I found it in Chapter 2, where Osterholm and Olshaker discuss the difference between disease transmission by droplets compared to aerosols.

Droplets are tiny globs of liquid that come out of your nose or mouth when, say, you sneeze or cough… As small and generally unnoticable as these particles may be, they’re heavy enough to fall to the ground by force of gravity. Droplets travel short distances or sink to the nearest surface. This is where the guidance for maintaining six feet of social distancing came from during the Covid pandemic...

Aerosol particles come out of your nose and mouth as droplets do… If I’m in a room speaking, within minutes, small particles expelled from my mouth and nose will be floating in the air, even though no one may see or feel them. If you’re in that room, you’re going to inhale my particles and exhale particles of your own…

Droplets come largely from coughing or sneezing, and the droplet hits you in your nose, eyes, or mouth, like an incoming projectile. Compare these droplets to the free-floating aerosol particles circulating from that same cough, sneeze, or even just breathing. The aerosols are present in that same six-foot ‘social distance’ zone as the droplets are, but aerosols are also potentially present even yards away. You can see how the transmission of a respiratory pathogen via an aerosol versus a droplet is a game changer in terms of the ease with which a virus can be spread.

Because this blog is about physics in medicine and biology, let’s examine some of the physics that distinguishes droplets from aerosols. Much of the physics we need is in Intermediate Physics for Medicine and Biology.

Consider the motion of a particle in still air. For the moment, we’ll neglect gravity. Newton’s second law gives us an equation for the particle’s speed, v, 

On the left is mass, m, times acceleration, dv/dt. One the right is Stokes’ law for the force of air friction. This doesn’t look exactly like Stokes’ law as written in IPMB because here we use the droplet’s diameter, d, instead of its radius, a, so the leading factor of six becomes three. The frictional force depends on the viscosity of the air, η. Anyone who has studied Chapter 2 of IPMB will recognize this differential equation as governing exponential decay. The velocity will decay with a time constant τ equal to m/3πηd. We prefer to write the mass in terms of the droplet’s density, ρ, where 

so 

 

This is the time needed for the particle’s speed to decay to zero relative to the air. Think of it as a relaxation time. If we had included the gravitation force, it would be the time constant for approaching a terminal speed. We know that the particle density will be close to the density of water, 1000 kg m^–3, and the viscosity of air is about 1.8 × 10^–5 N s m^–2. So, we can make a table giving the relaxation time for different particle diameters.

d (μm)	τ (s)
1	0.000003
10	0.0003
100	0.03
1000	3

After several of these time constants, the droplet will essentially flow with the air along a streamline. Because fluid flows parallel to a surface (a wall or ceiling), the particle will rarely hit a surface and adhere to it. Instead, it becomes part of the air we breathe.

What should we compare this relaxation time to? If you are in a room of size L, in which air is moving at a speed u, you can compare it to the time required to move across the room, L/u. If the room is 5 m long and has an air speed of 0.1 m s^–1 (typical for indoor air circulation), 50 s would be needed to cross that room. We could call this the circulation time. All the relaxation times in the above table are shorter than 50 s, so all these particles flow along streamlines (ignoring gravity). The ratio of the relaxation time to the circulation time is called the Stokes’ Number. It is a dimensionless number—like the Reynolds Number discussed in Chapter 1 of IPMB—that governs the particle motion. If you had a really big particle, say a centimeter in diameter, the relaxation time would be 300 s, and it would move more like a ballistic billiard ball or a bullet; it would not have time to approach the speed of the moving air before it slammed into the wall of the room. The air motion would then be more or less irrelevant.

Now let’s put gravity in. Newton’s second law for the particle speed becomes

where g is the acceleration of gravity (for our purposes, take it as 10 m s^–2). The particle will approach a terminal speed equal to gτ. If it approaches its terminal speed quickly (as the table above indicates it will), we can calculate the time T required for the particle to fall a distance H to the ground: T = H/gτ. Below I reproduce the table shown earlier, but with a column added for the fall time T. I’ll assume the fall distance is H = 2 m. 

d (μm)	τ (s)	T (s)
1	0.000003	67,000
10	0.0003	670
100	0.03	6.7
1000	3	0.067

For the 1 and 10 micron aerosols, the fall time is much longer than the time for the particle to travel across the room. It take minutes or even hours to fall. For a 100 micron particle, the fall time is somewhat less than the time to cross the room. It will travel a ways, but not too far. For the giant 1 mm droplet, it falls in less than a second. The time listed above is probably too small, because the particle would not have time to reach its terminal speed. But the time would still be much smaller than the time to cross the room. It would get the floor dirty, but a person a couple meters away would not breath it.

The key question is, how big are the particles we spew out when we have Covid? If they are 1 or 10 microns in size, they are truly aerosols and would spread throughout the room as the air circulated. If they are tiny, say 0.1 micron in size, they become similar to the size of the Covid virus itself, so our model begins to break down. If they are large 1 mm droplets, they fall to the ground quickly, and are not carried by the air. If they are about 100 microns in diameter, they are in a transition zone, and would behave a little like droplets and a little like aerosols (but, I think, mostly like droplets).

This all seems rather simple. Indeed, it’s a toy model of particle spread, useful for getting insights into the important parameters, but not terribly accurate. Stokes’ Law is not universally valid. The model does not include such features as diffusion, turbulence, buoyancy, and evaporation. But the model does confirm Osterholm and Olshaker’s main conclusion: If the particles are big (droplets), they fall quickly and may causes surfaces to become infectious but social distancing will probably prevent infection through the air. If the particles are small (aerosols), they move with the air circulation and can carry the virus to anyone in the same room or building. Apparently Covid produces aerosols, and that’s why it’s so transmissible. Osterholm and Olshaker’s fear is that the “big one”—a viral disease that causes some future horrible pandemic—will similarly be spread by aerosols and therefore be easily transmissible, but will be more deadly than Covid. Yikes!

Magnetism and its Effects on the Living System

In this blog, I’ve discussed several people who promote pseudoscience related to health effects of electric and magnetic fields, including Robert Becker and his book The Body Electric and Arthur Firstenberg and his book The Invisible Rainbow. Today I examine a pair of authors whose theories are, if anything, nuttier than Becker’s or Firstenberg’s: Albert Roy Davis and Walter Rawls. 

Are Electromagnetic Fields
Making Me Ill?

Here is what I write about these two in my book Are Electromagnetic Fields Making Me Ill?

Some of [Isaac Goiz] Duran’s ideas harken back to the bizarre notions of Albert Roy Davis and Walter Rawls, who believed that the north and south poles of magnets have dramatically different biological effects, even though the only difference between the poles is the direction of the field. For instance, they write that “when magnetic energy of the negative N [north] pole is applied to [a] cancer site, a remarkable reduction in the condition and also a marked arrest in further development of the cancer condition takes place… [whereas] when the S [south] pole of a magnet, this being the positive energy of a magnet, is applied to cancers they become more advanced and then develop, grow and spread at an accelerated rate.” Their ideas are not limited to explaining how magnetic fields interact with biological tissue, but require a complete revision of the electromagnetic theory expressed in Maxwell’s equations, which have formed the theoretical foundation for our understanding of electricity and magnetism for over 150 years, and are responsible for much of our modern technology. Indeed, Davis and Rawls immodestly declare that their readers “must be willing to leave behind them the outmoded, incorrect theories and concepts of magnetism [as formulated in Maxwell’s equations]” and insist that their view “offers a totally different picture than is now used in present textbooks and is used as law and theory in all related research.”

Do physicists really use an “outmoded and incorrect theory” to describe magnetism? Are Russ Hobbie and I teaching nonsense about biomagnetism in Intermediate Physics for Medicine and Biology? I don’t think so. 

Magnetism and its Effects
on the Living System

To give you a flavor of Davis and Rawls views, I obtained interlibrary loan a copy of their book Magnetism and its Effects on the Living System. The picture below (their page 22) show the traditional view of the magnetic field produced by the earth on the left (Davis and Rawls call it “the old”), and their revised view on the right (“the new”). The magnetic field near the equator is completely different in the two cases; in the traditional view the field is parallel to the earth’s surface, while in the revised view it is perpendicular to the surface. Davis and Rawls should have consulted the work of Alexander von Humboldt (1769–1859), who was one of the first to measure the dip angle of the earth’s magnetic field and map the magnetic equator. “The old” view is the correct view. 
 

Page 22 of Magnetism and its Effects on the Living System,
showing two hypotheses for the magnetic field of the earth.

In case you think that this is an unimportant detail that does not represent Davis and Rawls general theory, take a look at the picture they selected for their title page. 

Title page of Magnetism and its Effects on the Living System.

 

Davis and Rawls also believe that magnets can be used for pain relief. They write

The effects of applying N [north] pole magnetic energy to the nerves act to lower their sensitivity. This lowering of sensitivity allows us a certain control of a pain condition. When we transmit S [south] pole energies to the nerves they respond with a greater sensitivity to pain.

Yet, using magnets for pain has been proven to be ineffective. In my book Are Electromagnetic Fields Making Me Ill? I cite several clinical studies finding no effect. Magnetic fields do not provide pain relief, regardless of the polarity you use.

In addition, the authors claim that magnets can affect your brain.

In research experiments with small and advanced animals and man, in the case of willing subjects, we have found that the magnet’s NORTH POLE ONLY, when applied to the brain, can and will upgrade the senses of perception.

Again, no such effects have been found. Having an MRI does not influence how your brain works, regardless of if you lie in the bed feet-first or head-first. 

Why do I harp on people like Becker, Firstenberg, Davis, and Rawls? Am I beating a dead horse? After all, none of these authors are around now to defend themselves, and their views have been rejected by modern science. Why not let sleeping dogs lie? The main reason I bring them up is that people still cite these researchers and their books to advance their voodoo science ideas of how electric and magnetic fields influence the body. These views are both wrong and, at times, dangerous. They are not harmless eccentricities.

To be fair, I’ll give Davis and Rawls the final word: below I quote the last sentence of their book. Let me note that the book was written in 1974, over fifty years ago, and their hypotheses are all but forgotten, except by a few quacks.

Therefore, we hope this book will challenge the youth and the physicists of today, the scientific community as exploring scientists, to explore this new and exciting scientific probe, with a new outlook and new approach for a better world, the world of tomorrow. 

 

Listen to Walter Rawls describe his view of how magnetic fields affect the body. 
I disagree with what Rawls says, but you can watch the video and decide for yourself. 

 https://www.youtube.com/watch?v=gha_X7wApQc

Here Comes The Sun

Here Comes The Sun,
by Bill McKibben

I recently finished Bill McKibben’s excellent book Here Comes The Sun (McKibben and I are about the same age, so we both like the Beetles reference. The page just before the Table of Contents has a single line of text: “And I say, it’s all right.”). The subtitle is “A Last Chance for the Climate and a Fresh Change for Civilization.” It’s one of the most optimistic climate change books I have read.  After summarizing his past angst-ridden pronouncements on global warming, McKibben writes in the introduction to Here Comes The Sun “And yet, right now, really for the first time, I can see a path forward. A path lit by the sun.”

The heart of his argument is that now, finally, wind power and especially solar power have gotten so cheap that the change to green energy will be not only virtuous but also economically advantageous. In his book, McKibben addresses four questions that are often asked by green energy skeptics. I’ll look at them one by one.

Can We Afford it?

McKibben writes

Sometime in those 10 years [between 2014 and 2024] we passed some invisible line where producing energy pointing a sheet of glass at the sun became the cheapest way to produce power, and catching the breeze the second cheapest... As the energy investor Rob Carlson put it recently, continuing to burn fossil fuel is a “self-imposed financial penalty” that will “ultimately degrade America's long-term global competitiveness.”

The gist of his argument is that with fossil fuels, you have to pay for the fuel each and every time you use it to get energy. Year after year you keep paying for coal or oil or gas. With solar and wind energy, you pay once to set up the technology and then the fuel (the sun and wind) is free. FREE! FOREVER! (Or at least for the lifetime of the solar panel or wind turbine.)  I’m an cheapskate and I love free stuff. And you save the planet as a bonus. As McKibben points out, one problem is that energy becomes so cheap that energy companies can’t make money supplying it. What a wonderful problem to have.

But Can the Poor World Afford It? 

It turns out that the developing world is leapfrogging straight to solar power, skipping the centralized fossil fuel phase. Why?

The switch is being driven by the desire for reliable and affordable power. 

McKibben compares it to how cell phones allowed poor countries to skip the expensive land line infrastructure and go straight to mobile communication. Countries in Africa and the Middle East are right now putting up solar panels, with the process starting at the grass roots rather than from the top down. Who do they buy their solar panels from? China. 

But Is There Enough Stuff?

McKibben thinks the concerns about having enough raw materials such as lithium to build the solar panels, wind turbines, and batteries is a legitimate problem, but probably not an insurmountable one. 

Yes, you have to mine lithium to build a battery. But once you've mined it, that lithium sits patiently in the battery doing its job for a decade or two (after which, as we will see, it can be recycled). If you mine coal, on the other hand, you immediately set it on fire—that's the point of coal. And then it’s gone. And then you have to go mine some more.

He says we should compare the risks and cost of mining and recycling green energy materials to the much greater risks of mining and dealing with the left over from fossil fuels, such as coal ash.

Do We Have Enough Land?

The land needed for solar and wind is surprisingly small, especially compared to that taken up by fossil fuels. McKibben quotes an estimate that oil and gas wells, coal mines, pipelines, power plants, and the like take up about 1.3% of America’s land. Green energy will require far less. McKibben compares a solar array to a corn field.

Converting some of these [corn] fields to solar panels makes enormous ecological sense. That's because one way to look at a field of corn (or any other crop) is that it’s already an array of solar panels.  A plant is a way to convert sunshine into energy through photosynthesis... Somewhere between 1 and 3 percent of the sunlight falling on a leaf actually becomes energy. The photovoltaic panel works considerably better [20, and possibly some day up to 40, percent]...

You could supply all the energy the US currently uses by covering 30 million acres with solar panels. How much land do we currently devote to growing corn ethanol [not the corn we eat, but the corn we use to help fuel our cars]? About 30 million acres. 

The biggest threat is not a lack of land, but the not-in-my-backyard attitude so common in the USA. 

Because this is a blog about my textbook Intermediate Physics for Medicine and Biology, let’s do one of those estimation problems that Russ Hobbie and I encourage. The solar constant is 1390 W/m². That’s how much light energy from the sun per square meter that reaches the earth (or, at least, the top of our atmosphere). The cross-sectional area of our planet that intercepts this light is πR², where R is the earth’s radius (6.4 × 10⁶ m²). That gives 1.8 × 10¹⁷ W, or 180,000 TW (the “T” is for tera, or 10¹²). Humanity’s worldwide average power consumption is about 18 TW. So, we only need 0.01% of the solar energy available. Granted, some of that sunlight is reflected or absorbed by the atmosphere, some is incident on the ocean, and no solar panel is 100% efficient. Still, the land area needed for solar and wind farms, while not small, is reasonable. 

The Final Word

When I can, I like to give authors the final word in my blog posts. So, here is how McKibben ends Here Comes The Sun

I end this book saddened, too, of course—saddened by all that happened in the last 40 years, and by all that we haven’t done. But I also end it exhilarated. Convinced that we’ve been given one last chance. Not to stop global warming (too late for that) but perhaps to stop it short of the place where it makes civilization impossible. And a chance to restart that civilization on saner ground, once we’ve extinguished the fires that now both power and threaten it.

I’ve changed my mind. I’m gonna give George Harrison the final word.

Sun, sun, sun, here it comes.  

 

“Here Comes The Sun,” by the Beatles

https://www.youtube.com/watch?v=xUNqsfFUwhY 

   

Bill McKibben on Here Comes The Sun

https://www.youtube.com/watch?v=AADsgqz4nU4 

Science Under Siege

Science Under Siege,
by Michael Mann
and Peter Hotez.

I recently finished reading Science Under Siege: How to Fight the Five Most Powerful Forces That Threaten Our World, by Michael Mann and Peter Hotez. Mann is a climate scientist and Hotez develops vaccines. Both have been active in the fight against antiscience. Readers of this blog may recall my review of Hotez’s previous book The Deadly Rise of Antiscience. The authors state their purpose in the final paragraph of their preface.

In Science Under Siege we seek to provide a succinct yet detailed delineation of the five forces behind the modern-day antiscience movement (the five p’s, as we call them—the plutocrats, the petrostates, the pros, the propagandists, and our press). We draw upon our respective experiences on two different fronts of the war on science to identify and delineate the drivers and their financial backers. We provide a road map for dismantling the antiscience machine, through stories that at times are quite personal but speak to challenges and threats that are broad and sweeping. This book is a warning. But it is also a call to arms. While there is urgency—unlike any we’ve ever known—there is still agency. We can still avert disaster if we can understand the nature of the mounting antiscience threat and formulate a strategy to counter it.

In their first chapter they write

We find ourselves facing not just a one-two punch of pandemics and the climate crisis, but a one-two-three punch, with that third punch, antiscience, obstructing the needed response from governments and civil society. The future of humankind and the health of our planet now depend on surmounting the dark forces of antiscience.

My favorite chapter was their last one, titled “The Path Forward.” They present a Venn diagram for winning the war against antiscience.

 

About it they write

One circle describes ways to expand the visibility of scientists, while providing the tools for scientists to better engage with the public. Another characterizes efforts to protect scientists. And the remaining circle emphasizes the battle against the intensifying flow of antiscience disinformation. We propose a framework for accomplishing this tripartite mission.

I’m going to adopt this Venn diagram as a guide for my future posts. 1) I will continue to communicate constructively about Intermediate Physics for Medicine and Biology, but in addition I’ll stress how important science is in our society and oppose the forces of antiscience. I also will try to fulfill this role in my “Bob Park’s What’s New” series that I also publish weekly here. 2) I will search out and attempt to debunk and defeat disinformation. I’ve been trying to do this all along, but this goal is more urgent now. 3) I’ll support scientists. I can’t do much to support them financially or materially, but in this blog I can take on the role of cheerleader-in-chief and provide moral support, especially to those who are attacked by the forces of antiscience.

Mann and Hotez adopt a strident and pugnacious tone in Science Under Siege. Is it justified? It is. I truly believe that there is a Republican War on Science. I believe the forces of antiscience are currently winning this war. And I am certain we must oppose antiscience with all our resources. Particularly as a retired scientist, I have an obligation to fight antiscience for the sake of the next generation of scientists. And as a new grandfather, I must oppose antiscience for the sake of my grandson and all the others of his generation.

I’m going to end by repeating some inspiring words that Mann and Hotez feature. They’re from a commentary in the Journal of Virology titled “The Harms of Promoting the Lab Leak Hypothesis for SARS-CoV-2 Origins Without Evidence” (Volume 98, Article Number e01240–24, 2024). I suggest you read the entire article (it’s not long), but below is the excerpt Mann and Hotez quote.

Science is humanity’s best insurance against threats from nature, but it is a fragile enterprise that must be nourished and protected. What is now happening to virology is a stark demonstration of what is happening to all of science. It will come to affect every aspect of science in a negative and possibly dangerous way, as has already happened with climate science. It is the responsibility of scientists, research institutions, and scientific organizations to push back against the anti-virology attacks, because what we are seeing now may be the tip of the proverbial iceberg.

Book Talk: Michael E. Mann and Peter J. Hotez — Science Under Siege

https://www.youtube.com/watch?v=-foS1FIkK3g

Everything Is Tuberculosis

Everything Is Tuberculosis,
by John Green.

Recently I read the current bestseller Everything Is Tuberculosis: The History and Persistence of Our Deadliest Infection, by John Green. Tuberculosis is the deadliest infectious disease worldwide. According to Green,

Just in the last two centuries, tuberculosis [TB] caused over a billion human deaths. One estimate, from Frank Ryan’s Tuberculosis: The Greatest Story Never Told, maintains that TB has killed around one in seven people who’ve ever lived. Covid-19 displaced tuberculosis as the world’s deadliest infectious disease from 2020 through 2022, but in 2023, TB regained the status it has held for most of what we know of human history: Killing 1,250,000 people, TB once again became our deadliest infection. What’s different now from 1804 or 1904 is that tuberculosis is curable, and has been since the mid-1950s. We know how to live in a world without tuberculosis. But we choose not to live in that world…

Some of the symptoms of tuberculosis are difficulty breathing, coughing up blood, night sweats, and weight loss. It is a slowly progressing disease, which led to its now-archaic nickname “consumption.” Green writes

Some patients will recover without treatment. Some will survive for decades but with permanent disability, including lung problems, devastating fatigue, and painful bone deformities. But if left untreated, most people who develop active TB will eventually die of the disease.

In Chapter 1 of Intermediate Physics for Medicine and Biology, Russ Hobbie and I stress the importance of understanding the sizes of things. Tuberculosis is caused by bacteria, which are each a couple microns long and about a half a micron wide. But the body reacts to these bacteria by surrounding them with white blood cells and T cells of the immune system, “creating a ball of calcifying tissue known as a tubercle.” Tubercles vary in size, from a few tenths of a millimeter to a centimeter. That’s too big to pass through capillaries in the bloodstream and too big to fit into a single alveolus in the lungs.

IPMB only mentions tuberculosis twice. Russ and I write

Spontaneous pneumothorax [air between the lung and the chest wall] can occur in any pulmonary disease that causes an alveolus (air sac) on the surface of the lung to rupture: most commonly emphysema, asthma, or tuberculosis….

Some pathologic conditions can be identified by the deposition of calcium salts. Such dystrophic (defective) calcification occurs in any form of tissue injury, particularly if there has been tissue necrosis (cell death). It is found in necrotizing tumors (particularly carcinomas), atherosclerotic blood vessels, areas of old abscess formation, tuberculous foci, and damaged heart valves, among others.

This history of tuberculosis as a disease is fascinating. Green writes that in eighteenth century Europe “the disease became not just the leading cause of human death, but overwhelmingly the leading cause of human death.” Oddly, it became romanticized. People like the poet John Keats and the pianist Frederic Chopin died of tuberculosis, and the illness came to be linked with creativity. It also became associated with female beauty, as the thin, wide-eyed, rosy-cheeked appearance of a woman with tuberculosis became fashionable. Later, the disease was stigmatized, being tied to race and a lack of moral virtue. When a person suffered from tuberculosis, they often went to a sanatorium for rest and treatment, and usually died there.

The German microbiologist Robert Koch isolated Mycobacterium tuberculosis in 1882. Koch was a rival of Frenchman Louis Pasteur, and both worked on treatments. I was surprised to learn that author Arthur Conan Doyle—famous for his Sherlock Holmes stories—also played a role in developing treatments for the disease. Tuberculosis remains latent in people until it’s activated by some other problem, such as malnutrition or an immune system disease like AIDS. Many infectious diseases attack children or the elderly, but TB is common in young adults. Physicist Richard Feynman’s 25-year-old wife Arline died of tuberculosis.

Green explains that 

in the decades after the discovery of Koch’s bacillus, small improvements emerged. Better diagnostics meant the disease could be identified and treated earlier, especially once chest X-rays emerged as a diagnostic tool.

The main impact of medical physics on tuberculosis is the development of radiography. X-rays weren’t even discovered until 1895, a decade after Koch isolated the tuberculosis bacterium. They arrived just in time. The often-decaying bacteria at the center of a tubercle accumulates calcium. For low x-ray energies, when the photoelectric effect is the dominant mechanism determining how x-ray photons interact with tissue, the cross section for x-ray attenuation varies as the fourth power of the atomic number. Because calcium has a relatively high atomic number (Z = 20) compared to hydrogen, carbon, nitrogen, and oxygen (Z = 1, 6, 7, 8, respectively), and because lung tissue in general has a low attenuation because of the low-density of air, tubercles show up on a chest x-ray with a great deal of contrast.

The primary treatment for tuberculosis nowadays is antibiotics. The first one to be used for TB, streptomycin, was discovered in the 1940s. By the mid 1950s, several antibiotics made TB curable. I was born in 1960, just after the threat of tuberculosis subsided dramatically in the United States. I can still remember us kids getting those TB skin tests in our forearms, which we all had to have before entering school. But I don’t remember being very worried about TB as a child. The threat was over by then.

A vaccine exists for tuberculosis (the Bacillus Calmette–Guérin, or BCG, vaccine), but it’s mainly effective when given to children, and isn’t used widely in the United States, where tuberculosis is rare. In poorer countries, however, the vaccine saves millions of lives. Currently, mRNA vaccines are being developed against TB. This crucial advance is happening just as Robert F. Kennedy, Jr. is leading his crazy anti-science crusade against vaccines in general, and mRNA vaccines in particular. The vaccine alliance GAVI is hoping to introduce new vaccines for tuberculosis, and this effort will certainly be hurt by the United States defunding GAVI. The World Health Organization has an “end TB strategy” that, again, will be slowed by America’s withdraw from WHO and the dismantling of USAID. Green’s book was published in 2025, but I suspect it was written in 2024, before the Trump administration’s conspiracy-theory laden effort to oppose vaccines and deny vaccine science got underway.

Many of these world-wide efforts to eliminate TB depend on access to new drugs that can overcome drug-resistant TB. Unfortunately, such drugs are expensive, and are difficult to afford or even obtain in poorer countries.

In the final pages of Everything is Tuberculosis, Green writes eloquently

...TB [tuberculosis] in the twenty-first century is not really caused by a bacteria that we know how to kill. TB in the twenty-first century is really caused by those social determinants of health, which at their core are about human-built systems for extracting and allocating resources. The real cause of contemporary tuberculosis is, for lack of a better term, us...

We cannot address TB only with vaccines and medications. We cannot address it only with comprehensive STP [Search, Treat, Prevent] programs. We must also address the root cause of tuberculosis, which is injustice. In a world where everyone can eat, and access healthcare, and be treated humanely, tuberculosis has no chance. Ultimately, we are the cause.

We must also be the cure.

Green serves on the board of trustees for the global health non-profit Partners In Health. To anyone wanting to join the worldwide fight against tuberculosis, I suggest starting at https://www.pih.org.

 

John Green reads the first chapter of Everything Is Tuberculosis.

https://www.youtube.com/watch?v=CCbDdk8Wz-8

John Green discusses Everything Is Tuberculosis on the Daily Show

https://www.youtube.com/watch?v=2uppLo4lZRc

The Air They Breathe

I’m used to thinking about climate change from a physics perspective: what technologies can we use to reduce the amount of carbon dioxide and methane going into the atmosphere. Even when I consider the health effects of climate change, I tend to focus on the technical aspects (as you might expect from an author of a book titled Intermediate Physics for Medicine and Biology). Moreover, I often consider the long-term risks of climate change, and how it will harm future generations.

The Air They Breathe,
by Debra Hendrickson.

In her wonderful new book The Air They Breathe: A Pediatrician on the Front Lines of Climate Change, Debra Hendrickson has a different perspective. She explains how climate change is harming her young patients today. Specifically, she highlights four ways they are in danger.

1. Bad air from burning fossil fuels and from forest fires caused by climate change hurts children, particularly those with breathing problems like asthma. Here in Michigan, sometimes climate change seems a distant threat. But I remember the summer of 2023, when the air in the Detroit area was filled with smoke from fires in Canada. Hendrickson often makes her points by examples of specific children, such as a young girl named Anna, whose asthma was worsened by a forest fire burning near her home in Reno, Nevada in 2013. In The Air They Breathe, Hendrickson writes

Since Anna’s visit to my clinic that afternoon, thousands of other wildfires have raged through California, just a few miles to our west. They have grown bigger and more explosive, devouring not just forests, but towns. Every summer and fall now, waves of smoke pass through my city, and more of my young patients cough and wheeze. In 2018, the Mendocino Complex wildfire would become the largest California had ever seen, darkening the skies for weeks. Only two years later, in 2020, the August Complex fire would shatter that record, becoming the first to burn more than a million acres. And in 2021 we spent not just days breathing smoke, as we did in 2013, but months, as both the Dixie and Caldor fires raged a few miles away.

When I look back today, I see that the Rim Fire was not an isolated event, as it seemed to us then; it was the beginning of a trend. It was a sample of the world we are creating for our children.

2. Excessive heat can cause heatstroke in children, particularly in infants left in hot cars and high school football players who practice in the extreme heat. Children are especially sensitive to overheating. Heat waves can kill. Hendrickson tells the story of Joey Azuela, a child who almost died when hiking on a hot summer day near Phoenix, Arizona, saved only after being rushed to a hospital where he was covered with ice and injected with cold saline. She writes

Heatstroke is treated with extreme urgency; minutes make the difference between life and death. Joey Azuela is alive because he was cooled so quickly. Yet as the world watches temperatures climb, we drift, and delay; we risk pushing the planet to tipping points of rapid and uncontrollable changes, from which we cannot recover. The speed of our response is everything. It will determine not just the type of future our children have, but whether they have a future, at all.

3. Trauma and post traumatic stress disorder can occur in children who experience disasters caused by climate change, such as a hurricane, flood, or forest fire. Hendrickson examines in particular how in 2017 hurricane Harvey dumped as much as 40 inches of rain on Houston, Texas. One boy, Lucus, had to escape the rising water with his mother and siblings from their neighbor’s roof, saved by a passing boat. She writes

Natural disasters have always plagued us; the events themselves are nothing new. But a warming world is turning up their dial, and with it, the potential for trauma. Though some years are better than others, weather-related catastrophes are clearly trending worse over time: becoming more frequent, more powerful, and more destructive. Globally, natural disasters have increased fivefold over the last half century. Extreme weather events—the worst examples of these disasters, like 100-year floods and Category 4 hurricanes—are growing steadily more severe, and more common.

4. Infectious diseases, such as an increase in malaria caused by a greater range for mosquitoes, are becoming more common with global warming. Hendrickson tells us about Darah, an infant born in New Jersey who got the Zika virus from her mother while in the womb, and who suffered from microcephaly: an underdeveloped brain. She explains

To understand the connection between climate change and Darah’s case, we have to zoom out from her small New Jersey apartment and see that she shares this planet with trillions of other living things. That her body is linked to the Earth not just by water and air, but by a rich sea of organisms, friend and foe, living within and around her. Many of them are being affected by rising temperatures and shifting rains; by changes in habitats and seasons.

One point this book makes clear is the health care and climate change are not separate issues. The two are intertwined. Another point is that this is not merely a problem that we will all face in the coming decades. It’s happening now, as described by the horrific stories of these children. I found this book to be a call to action. It motivates me to make an even greater effort to address global warming, because—as Hendrickson warns us—“The only heroes our children have are us.”

Vaccines Did Not Cause Rachel's Autism

Vaccines Did Not
Cause Rachel’s Autism,
by Peter Hotez.

I recently listened to an audio recording of Peter Hotez’s book Vaccines Did Not Cause Rachel’s Autism: My Journey as a Vaccine Scientist, Pediatrician, and Autism Dad. Hotez is the same author who wrote The Deadly Rise of Anti-Science, which I reviewed previously in this blog. I’m troubled by the current anti-vaccine sentiment, which is foolish and dangerous. Along with climate change denial, vaccine hesitancy is a worrisome example of an alarming anti-science movement in the United States.

Hotez’s book provides insight into the challenges faced by parents with autistic children (by the way, Peter Hotez is not the hero of this book; the hero is his wife Ann). Moreover, the book makes a compelling argument that vaccines do not cause autism. Hotez reviews much of the scientific literature relevant to the relationship of vaccines to autism. In particular, he mentions a meta-analysis of clinical studies published by a group from Australia. As much as I enjoyed and admired Hotez’s book, I probably would have led off by discussing that publication, rather than waiting until late in the book to bring it up.

“Vaccines are Not Associated With Autism:
An Evidence-Based Meta-Analysis of
Case-Control and Cohort Studies”
by Taylor, Swerdfeger, and Eslick,
Vaccine, 32:3623–3629, 2014.

Today I’ll discuss that article, titled “Vaccines are Not Associated With Autism: An Evidence-Based Meta-Analysis of Case-Control and Cohort Studies” by Luke Taylor, Amy Swerdfeger, and Guy Eslick. This paper appeared in 2014 in the journal Vaccine (Volume 32, Pages 3623–3629). The abstract appears below.

There has been enormous debate regarding the possibility of a link between childhood vaccinations and the subsequent development of autism. This has in recent times become a major public health issue with vaccine preventable diseases increasing in the community due to the fear of a ‘link’ between vaccinations and autism. We performed a meta-analysis to summarise available evidence from case-control and cohort studies on this topic (MEDLINE, PubMed, EMBASE, Google Scholar up to April, 2014). Eligible studies assessed the relationship between vaccine administration and the subsequent development of autism or autism spectrum disorders (ASD). Two reviewers extracted data on study characteristics, methods, and outcomes. Disagreement was resolved by consensus with another author. Five cohort studies involving 1,256,407 children, and five case-control studies involving 9,920 children were included in this analysis. The cohort data revealed no relationship between vaccination and autism (OR: 0.99; 95% CI: 0.92 to 1.06) or ASD (OR: 0.91; 95% CI: 0.68 to 1.20), nor was there a relationship between autism and MMR (OR: 0.84; 95% CI: 0.70 to 1.01), or thimerosal (OR: 1.00; 95% CI: 0.77 to 1.31), or mercury (Hg) (OR: 1.00; 95% CI: 0.93 to 1.07). Similarly the case-control data found no evidence for increased risk of developing autism or ASD following MMR, Hg, or thimersal exposure when grouped by condition (OR: 0.90, 95% CI: 0.83 to 0.98; p = 0.02) or grouped by exposure type (OR: 0.85, 95% CI: 0.76 to 0.95; p = 0.01). Findings of this meta-analysis suggest that vaccinations are not associated with the development of autism or autism spectrum disorder. Furthermore, the components of the vaccines (thimersal or mercury) or multiple vaccines (MMR) are not associated with the development of autism or autism spectrum disorder.

Some of the terms and concepts mentioned in the abstract may be unfamiliar, so let me explain them.

• Autism and Autism Spectrum Disorders. Autism is a disorder of the nervous system that begins during the development of a fetus. An autistic person may engage in repetitive, inflexible behaviors or have problems interacting with people. The disorder can vary in its severity and symptoms, so people with different degrees of severity are said to be on the autism spectrum.
• Vaccine. A vaccine is a biological agent that stimulates a person’s immune system to recognize and destroy a microorganism causing an infectious disease. Vaccines are often made from a weakened form of the microbe.
• The MMR Vaccine. The MMR vaccine protects children against three diseases: measles, mumps, and rubella (German measles). An initial dose of the MMR vaccine is typically given around a child’s first birthday and a second dose before entering school. It’s usually given by injection.
• Thimersal-Containing Vaccine. Thimersal is a molecule containing mercury. The element mercury, whose chemical symbol is Hg, is a known toxin. However, not all molecules containing mercury are as toxic as is mercury metal itself. Mercury compounds like thimersal are used in low doses as a preservative in some vaccines. Before 1991, thimersal was included in the childhood vaccine DPT which protects against diphtheria, tetanus (lockjaw), and pertussis (whopping cough). Now no childhood vaccines contain thimersal, although it’s still used in some flu vaccines.
• Meta-Analysis. Meta-analysis is a statistical method of analyzing and summarizing several clinical trials. A meta-analysis can increase the number of patients being analyzed, resulting a more statistical power. It can also help in resolving studies with inconsistent results.
• Case-Control Study. A case-control study is a clinical study that compares two groups: one having a disease and one not (the control). It is often retrospective, meaning it uses existing data from people known to have a disease, and therefore can be conducted quickly.
• Cohort Study. A cohort study is a clinical trial that takes a group of people and follows them through time to determine what fraction develop some disease. It is prospective, collecting data on exposure to some suspected cause. A cohort study can take a long time to complete and, for a rare disease, requires studying a large population, but it’s less susceptible to bias than a case-control study.
• Odds Ratio. The odds ratio (OR) is a statistical measure to determine if some factor has an effect. For example, suppose in a case-control study you examined the medical records of 600 people who had the MMR vaccine; 570 were healthy but 30 had autism (the odds of being healthy are 570:30, or 19:1). As a control, you examined the medical records of 400 people who did not have the MMR vaccine; 380 were healthy but 20 had autism (the odds of being healthy are 380:20, or 19:1). In that case, the odds ratio would be
  
  When the odds ratio is one, you conclude the MMR vaccine had no effect (the odds of having autism are the same whether or not you had the vaccine). If, however, among the 600 people who had the MMR vaccine 510 were healthy and 90 had autism (with the control group being unchanged from that given above) then the odds ratio would be
  
  In this case, the MMR vaccine would have a clear effect. For smoking and lung cancer, the odds ratio is quite large, about 10.
• 95% Confidence Interval. How large must the odds ratio be in order to conclude there is some effect? That depends on how much uncertainty there is. For instance, if you flip a coin four times, the most likely result is two heads and two tails. However, there is still one chance out of sixteen, about 6%, that you’ll get four heads. If you want to be more certain that a coin is fair and not biased, you would need to flip the coin more than four times. In the same spirit, to completely characterize how much confidence you have in the result of a clinical trial, you must indicate how large the uncertainty is in the result. Most clinical studies will give the odds ratio and a range of values for which—based on a statistical analysis—there is a 95% chance that the odds ratio is within that interval. The convention is that if the 95% confidence interval does not contain the value of one, then there is a statistically significant effect. If it does contain one, any effect is not statistically significant. Using a value of 95%, rather than say 98%, is arbitrary, but you have to draw the line somewhere, and 95% confidence is the usual medical criteria for significance. For example, if in one of these autism studies the odds ratio was 1.05 and the 95% confidence interval was 0.8 to 1.3, you would conclude that there is not a statistically significant effect of the vaccine. If, on the other hand, the odds ratio were 1.05 and the 95% confidence interval was 1.02 to 1.08, you would conclude there is a small but statistically significant effect of the vaccine on autism. Note that in statistics the word “significance” does not mean “important.” It means “unlikely to be due to chance.” One virtue of a meta-analysis is that by combining several studies the number of people analyzed increases, which can shrink the 95% confidence range, which provides better statistical power to say if the odds ratio is significantly different than one. 
• p-value. Whenever you have an arbitrary threshold, like saying a result is or is not statistically significant, you worry about cases that are near the threshold. To provide additional information, researchers sometimes give the p-value. It is the probability that a result at least this extreme could happen by chance. In medicine, usually p = 0.05 is the cutoff between a result being considered significant or not significant. But if the result has p = 0.03, you might say it is significant (less than 0.05) but you might think that it is still questionable and maybe you should repeat that study with a larger number of people. On the other hand, if p = 0.0002 you would say that the result almost certainly didn’t happen by chance and you would therefore have a lot of confidence in it. In this meta-analysis, the p-value is sometimes given, especially for borderline cases, to help the reader estimate the true significance of the result.
• MEDLINE, PubMed, EMBASE, Google Scholar. These databases contain information about scientific publications, including articles describing clinical trials. They can be searched using various keywords to find publications about a particular subject. MEDLINE is a database compiled by the National Library of Medicine, and covers all biomedical research. It can be searched online using a tool called PubMed, which includes MEDLINE plus a few other databases. EMBASE is an international database that focuses on the pharmaceutical industry. Google Scholar is a free web search engine that covers all scholarly publications.

Now that we understand the vocabulary, what does this meta-analysis show? It indicates that there is no evidence supporting a connection between vaccines and the development of autism. It also shows there is no risk that thimersal or mercury causes autism. In fact, some of the results suggest a weak protective effect caused by thimersal. For example, an odds ratio of 0.85 with a 95% confidence interval of 0.76 to 0.95 suggests that the odds ratio may be slightly less than one, which means the vaccine prevents people from getting autism. However, the p-value for this result was 0.01 which is small but not that small, and I wouldn’t put too much confidence in the claim that the vaccine is protective. But the results sure don’t suggest there is a health risk.

What I’ve analyzed today is one paper, albeit a meta-analysis. It’s over ten years old. There are lots of other data out there now, and Hotez describes some of it in Vaccines Did Not Cause Rachel’s Autism. He also emphasizes that autism is thought to arise from problems during the development of a fetus, long before the child receives any vaccines, so there’s no reason to suspect vaccines as a cause of autism. All this evidence, taken together, implies the probability of vaccines causing autism is extremely low.

Why do people still claim vaccines cause autism? There will certainly be cases where a child will receive a vaccine and then start showing symptoms of being on the autism spectrum. Some might point to such cases and say “see, I told you so!” The question is, how many of those children would have started showing symptoms of autism even if they didn’t get the vaccine? Homework problem 9 in Chapter 3 of Intermediate Physics for Medicine and Biology explores this type of question quantitatively. The reason you need a large, controlled statistical study is so you’re not fooled by a few such coincidences.

One thing clinical studies, such as the one that I discussed today, cannot give you is certainty. You can’t say with absolute certainty (p = 0) that vaccines don’t cause autism. Science doesn’t deal in certainties, just probabilities. All you can say is that the evidence suggests there is no connection between vaccines and autism. The best you can do is to collect enough evidence so that the probability of a relationship is very small. That is where we are today. The probability of vaccines causing autism is extremely low. That’s the best conclusion science can offer. And when the probability is vanishingly small, we often feel confident in summarizing the situation with a simple (if somewhat too simple) declarative sentence, such as Vaccines Did Not Cause Rachel’s Autism.

Outbreak News TV: Vaccines Did Not Cause Rachel's Autism.

https://www.youtube.com/watch?v=xDh3QZPx2ns&t=461s

Peter Hotez wins award for Scientific Freedom and Responsibility.

https://www.youtube.com/watch?v=WHtWmSz4cXE

Dr. Peter Hotez's mission to make a difference.

https://www.youtube.com/watch?v=xC-3ofA1hIE

The Song of the Dodo

The Song of the Dodo,
by David Quammem.

One of my favorite science writers is David Quammen. I’ve discussed several of his books in this blog before, such as Breathless, Spillover, and The Tangled Tree. A copy of one of his earlier books—The Song of the Dodo: Island Biogeography in an Age of Extinctions—has sat on my bookshelf for a while, but only recently have I had a chance to read it. I shouldn’t have waited so long. It’s my favorite.

Quammen is not surprised that the central idea of biology, natural selection, was proposed by two scientists who studied islands: Charles Darwin and the Galapagos, and Alfred Russell Wallace and the Malay Archipelago. The book begins by telling Wallace’s story. Quammen calls him “the man who knew islands.” Wallace was the founder of the science of biogeography: the study of how species are distributed throughout the world. For example, Wallace’s line lies between two islands in Indonesia that are only 20 miles apart: Bali (with plants and animals similar to those native to Asia) and Lombok (with flora and fauna more like that found in Australia). Because islands are so isolated, they are excellent laboratories for studying speciation (the creation of new species through evolution) and extinction (the disappearance of existing species).

Quammen is the best writer about evolution since Stephen Jay Gould. I would say that Gould was better at penning essays and Quammen is better at authoring books. Much of The Song of the Dodo deals with the history of science. I would rank it up there with my favorite history of science books: The Making of the Atomic Bomb by Richard Rhodes, The Eighth Day of Creation by Horace Freeland Judson, and The Maxwellians by Bruce Hunt.

Yet, The Song of the Dodo is more than just a history. It’s also an amazing travelogue. Quammen doesn’t merely write about islands. He visits them, crawling through rugged jungles to see firsthand animals such as the Komodo Dragon (a giant man-eating lizard), the Madagascan Indri (a type of lemur), and the Thylacine (a marsupial also known as the Tasmanian tiger). A few parts of The Song of the Dodo are one comic sidekick away from sounding like a travel book Tony Horwitz might have written. Quammen talks with renowned scientists and takes part in their research. He reminds me of George Plimpton, sampling different fields of science instead of trying out various sports.

Although I consider myself a big Quammen fan, he does have one habit that bugs me. He hates math and assumes his readers hate it too. In fact, if Quammen’s wife Betsy wanted to get rid of her husband, she would only need to open Intermediate Physics for Medicine and Biology to a random page and flash its many mathematical equations in front of his face. It would put him into shock, and he probably wouldn’t last the hour. In his book, Quammen only presents one equation and apologizes profusely for it. It’s a power law relationship

S = c Aⁿ .

This is the same equation that Russ Hobbie and I analyze in Chapter 2 of IPMB, when discussing log-log plots and scaling. How do you determine the dimensionless exponent n for a particular case? As is my wont, I’ll show you in a new homework problem.

Section 2.11

Problem 40½. In island biogeography, the number of species on an island, S, is related to the area of the island, A, by the species-area relationship: S = c Aⁿ, where c and n are constants. Philip Darlington counted the number of reptile and amphibian species from several islands in the Antilles. He found that when the island area increased by a factor of ten, the number of species doubled. Determine the value of n.

Let me explain to mathaphobes like Quammen how to solve the problem. Assume that on one island there are S₀ species and the area is A₀. On another island, there are 2S₀ species and an area of 10A₀. Put these values into the power law to find S₀ = cA₀ⁿ and 2S₀ = c(10A₀)ⁿ. Now divide the second equation by the first (c, S₀, and A₀ all cancel) to find 2 = 10ⁿ. Take the logarithm of both sides, so log(2) = log(10ⁿ), or using a property of logarithms log(2) = n log(10). So n = log(2)/log(10) = 0.3. Note that n is positive, as it should be since increasing the area increases the number of species.

When I finished the main text of The Song of the Dodo, I thumbed through the glossary and found an entry for logarithm. “Aww,” I thought, “Quammen was only joking; he likes math after all.” Then I read his definition: “logarithm. A mathematical thing. Never mind.”

About halfway through, the book makes a remarkable leap from island biogeography—interesting for its history and relevance to exotic tropical isles—to mainland ecology, relevant to critical conservation efforts. Natural habitats on the continents are being broken up into patches, a process called fragmentation. The expansion of towns and farms creates small natural reserves surrounded by inhospitable homes and fields. The few remaining native regions tend to be small and isolated, making them similar to islands. A small natural reserve cannot support the species diversity that a large continent can (S = c Aⁿ). Extinctions inevitably follow.

The Song of the Dodo also provides insight into how science is done. For instance, the species-area relationship was derived by Robert MacArthur and Edward Wilson. While it’s a valuable contribution to island biogeography, scientists disagree on its applicability to fragmented continents, and in particular they argue about its relevance to applied conservation. Is a single large reserve better than several small ones? In the 1970s a scientific battle raged, with Jared Diamond supporting a narrow interpretation of the species-area relationship and Dan Simberloff advocating for a more nuanced and less dogmatic view. As in any science, the key is to get data to test your hypothesis. Thomas Lovejoy performed an experiment in the Amazon to test the species-area relationship. Parts of the rainforest were being cleared for agriculture or other uses, but the Brazilian government insisted on preserving some of the native habitat. Lovejoy obtained permission to create many different protected rainforest reserves, each a different size. His team monitored the reserves before and after they became isolated from adjacent lands, and tracked the number of species supported in each of these “islands” over time. While the results are complicated, there is a correlation between species diversity and reserve size. Area matters.

One theme that runs through the story is extinction. If you read the book, you better have your hanky ready when you reach the part where Quammen imagines the death of the last Dodo bird. Conservation efforts are featured throughout the text, such as the quest to save the Mauritius kestrel.  

 

The Song of the Dodo concludes with a mix of optimism and pessimism. Near the end of the book, when writing about his trip to Aru (an island in eastern Indonesia) to observe a rare Bird of Paradise, Quammen writes

The sad, dire things that have happened elsewhere, in so many parts of the world—biological imperialism, massive habitat destruction, fragmentation, inbreeding depression, loss of adaptability, decline of wild populations to unviable population levels, ecosystem decay, trophic cascades, extinction, extinction, extinction—haven’t yet happened here. Probably they soon will. Meanwhile, though, there’s still time. If time is hope, there’s still hope.

An interview with David Quammen, by www.authorsroad.com

https://www.youtube.com/watch?v=Quq7PNH1zWM