Map of life expectancy at birth from Global Education Project.

Friday, September 15, 2006

Return to the Magic Mountain?

A major controversy in public health in the late 20th Century concerned the work of Thomas McKeown, who argued that medical intervention had little to do with the decline in death rates and growth of population in the industrialized countries prior to the 20th Century. Rather, he argued, economic growth and attendant better living conditions, particularly better nutrition, were principally responsible.

McKeown was aggressively attacked and, as James Colgrove put it, (American Journal of Public Health, March 2002): "The consensus among most historians about the McKeown thesis a quarter century after it first stirred controversy is that one narrow aspect of it was correct -- that curative medical measures played little role in mortality decline prior to the mid-woth century -- but that most of its other claims, such as the assessment of the relative contributions of birth rates and of public health and sanitation measures to population growth, were flawed."

This is now supposed to be the smart kids' view of McKeown, but I find it quite odd. That is not a "narrow aspect" of McKeown's thesis -- it is what most readers found to be most essential about it. It's pretty much the whole point. Granted, he offended public health practitioners by playing down the clean water thing, and he was probably wrong about that. However, his most famous analysis had to do with the decline in tuberulosis mortality in England and Wales. TB used to be a major killer, but it had become rare before there were any effective medical treatments. Remember how much of 19th Century literature is about TB, from Mann to Keats to Alexandre Dumas? But who ever worried about it in the 1930s? McKeown's foremost critic, Simon Szreter (yup, I spelled that correctly) argued that he had confused tuberculosis and other respiratory diseases in death records, and so gotten the timing of the decline of tuberculosis wrong. This was all supposed to be quite devastating, but it is really nit picking. It remains true that TB became unimportant as a cause of death in the developed countries before effective treatments came along.

Anyway, I dredge all this up today because of the considerable alarm that has arisen over the emergence of so-called Extensively Drug Resistant Tuberculosis (XDR TB) in many areas of the world, particularly in association with HIV. It appears that drug resistant strains have arisen independently in various places.

As you know if you've been reading for a while, drug resistant pathogens result, among other causes, from erratic use of antibiotics or failure to complete courses of treatment. Tuberculosis can infect people without producing symptoms. It is most likely to cause illness in people who are immunocompromised or generally debilitated, and of course it is people with active symptoms, who are coughing and bringing up sputum, who are most likely to be infectious, and most likely to be caught by people who are in close proximity with infected people in poorly ventilated circumstances such as prisons or shelters for the homeless. So we can see why TB would decline with improving living conditions, and why TB is mostly seen today in conjunction with HIV, in poor countries, and among socially marginalized people in the rich countries.

So, the appearance of XDR TB is worrisome. TB control depends on antibiotics, and if we lose them, TB could once again become disastrous for humanity. Recommended measures include making sure to add multiple new drugs to regimens that prove ineffective, instead of just one; and so-called Directly Observed Therapy, making sure that people take all their pills; and finding as many cases of TB as possible and bombing them with multiple, powerful antibiotics. In this way, it is hoped, we can keep a lid on the problem.

Still, I wonder if we shouldn't give poor old McKeown more credit in this situation. Eliminating the social disadvantages which help TB thrive in the human population would help just as much, if not more. But that's obviously unrealistic.

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