CATEGORY / epidemiology

More Self Plugging

My latest serious article is published in India Currents magazine. Here’s a taste:


Years ago, I interviewed for a job with a law firm that was looking for an epidemiologist with skills in science research design. Their intent was that I would attack the science underlying the claims being brought against their major clients—mostly tobacco companies being sued for smoking-related health damages.

“If I took this job, how would I sleep at night?” I asked myself. “On a bed of money,” came the subconscious reply.

I ultimately chose another path, but the lesson was learned: though there is an undeniable causal link between smoking and poor health, there are sufficient cracks in the scientific methodology used to quantify that link that a disingenuous expert could likely foment doubt among non-expert jurors, simply by prising those cracks into yawning chasms. In essence, one can use science’s own persnickety nature to attack it…


What We’ve Learned From AIDS


Today (or, more precisely, yesterday) was World AIDS Day, whose intent and focus is fairly self-evident. To mark the day, activist and educational events took place the world over, including at the University of Ottawa. Several of my international health students organized and took part in such events, many of which took place over the week leading up to World AIDS Day. I must say, the few student run events that I was able to observe really impressed me. I am extremely proud of these young women and men; teaching them is a joy –though sometimes also a pain in the ass. But mostly a joy. HIV/AIDS is, of course, the great scourge of our time. Malaria kills more people. Diarrhea kills more children. Tuberculosis has a greater global burden. Mental illness has a greater global disability burden. But HIV/AIDS is a particularly insidious disease that cripples economies and eradicates whole societies. In some communities in sub-Saharan Africa, society has been decapitated by the disease, with only small children left to exist in a world devoid of adults. A generation of dispossessed orphans results, with the economic, political and moral impact that such a phenomenon represents. Yet, at one of the World AIDS Day events, my friend and colleague Dr. Paul MacPherson mentioned that, in some ways, AIDS has had a positive impact on the world. His statement has inspired me to list some of the ways in which HIV/AIDS has changed us for the better:

  • We now have an undertanding of immunology light years beyond what we knew before the epidemic.
  • Nations have been forced to come together and forge agreements –such as TRIPS— around the licensing of generic drugs and other such emergency measures which will come into play in future epidemics.
  • Many societies have been forced to consider the civil rights of homosexuals.
  • Heretofore powerful and seemingly selfish individuals, like Bill Gates, have stepped up to create organizations dedicated to the public good.
  • Issues like debt relief and other forms of large scale international development have reached the mainstream agenda.
  • We have developed educational and administrative controls over blood products and sexual behaviours which can be employed by public health forces to address other diseases, like hepatitis and STIs.
  • Common citizens, politicians and businessmen have been forced to learn more science.
  • The plight of Africa has inched ever so closer to the front page.
  • Entire new industries, focused on international health and development, have arisen.
  • The epidemic has inspired art, activism, organization and engagement in circles that otherwise might have remained apathetic.

Got any more?

When The Condom Breaks, The Cradle Will Fall…

Newsflash: I am an epidemiologist. One of the important dimensions of epidemiology is using indicators correctly. I stress to my students that it’s important to consider when to use a relative measure vs. an absolute measure.

For example, there were 6 cases of cholera in the USA in 1999 (MMWR, 1999). Every case of cholera makes public health officials very nervous, because it may signal a potential outbreak. But 6 cases constitute a prevalence rate that is vanishingly small.

In 1998, there were 5 new cases of cholera. The additional case in 1999 meant an increase of 20%! A 20% incidence increase in any disease sets off public health alarm bells. But, really, there were only 6 cases in total. No biggy.

The relative measure was a 20% increase. The absolute measure was a single new case. Depending on which statistic you look at, you get a whole different picture of the cholera burden of the USA.

Now, my public health colleagues are going to have a fit over what I’m going to talk about next…

A recent study concluded that 30% of women who date online have had sex on the first date with gentlemen they’ve met online. (Zod bless those fine, upstanding women). Moreover, the study found that 77% of these women had had unprotected sex in those encounters. Of course, public health officials are outraged. The STI specialist quoted in the linked articled said,

“When you have unprotected sex with people you are meeting online, you are playing russian roullette [sic] with your health. It’s not a matter of ‘if’ you’ll get a sexually transmitted disease, but rather ‘when’ and ‘how many’.”

Well, I’m here to report that, epidemiologically, this is a bit of hyperbole.

There is no question that STDs/STIs are bad. There is no question that globally, and among some sub-populations, they exist in epidemic proportions. There is no question that one should always err on the side of protection, and wear a condom to protect oneself from pregnancy, STIs and overall ooginess.

However, that is no reason to conflate the risks suggested by the actual numbers! Let’s break it down..

In Canada, chlamydia is overwhelmingly the most common STI. The most recent reliable stats we have are from 2004. In that year, there were a total of nearly 63,000 cases detected. Chlamydia is a reportable disease, which means that the government is notified of every detected case; almost none fall through the cracks. Undiagnosed cases are, of course, unknowable, but are often tracked down if the infected person spreads it to others. In other words, 63,000 is probably a fairly accurate estimate of the chlamydia burden of Canada. (Compare this to about 9000 cases of gonorrhea and maybe 1000 cases of syphilis… very roughly.)

The Canadian STI surveillance report states that STIs are on the rise. Public health officials are worried about this trend. I’ve heard some use the word “epidemic”. In terms of chlamydia, there was a 70% rise from 1997 to 2004, from 113.9 to 197.1 per 100,000 population. The current prevalence is164 cases per 100,000 population, or about 0.16% of the total population, assuming a conservatively estimated base population of 35 million.

A 70% rise is a staggering number that necessarily warrants concern. But the prevalence is still only 0.16%. That means that probabilistically, you’d have to have unprotected sex with 625 random people before you were guaranteed to be exposed to someone with chlamydia.

Now let’s break it down further. Let’s say you’re one of these single on-line women, aged 35, currently disease free. The age-specific chlamydia burden among Canadian men aged 25+ is 9374 cases. Using an adult male population of about 20 million, that gives us a prevalence estimate of 0.05%. Thus, one of these single women would then have to have unprotected sex with 2000 random men in order to guarantee being exposed to chlamydia.

So far I’ve been talking about the chances of being exposed to an STI. What about actually contracting one? Well, the transmission rate of chlamydia is between 30% and 40%. In other words, only 30-40% of sexual encounters with an infected person will result in the disease being transmitted. This means that our hypothetical woman, in a worst case scenario, would have to have unprotected sex with 5000 random Canadian men before being guaranteed to contract chlamydia. And, of course, the number is even more outrageous for the less common STIs.

Given these numbers, I think our STI specialist above was being a tad hyperbolic when he said such women were guaranteed to become infected. Don’t you agree? To him I say, “Get a freakin’ grip, buddy.”

The truth is, thousands of people around the country are having unprotected sex all the time, and nothing bad is going to happen to most of them. This is not a reason to advocate unprotected sex– not at all. Do not mistake what I am saying! I am not condoning unprotected sex. Even a 0.16% risk is too much to always take lightly, in my opinion, when you can reduce it to near zero by using very basic controls, like a condom.

Rather, it is never justifiable to exaggerate risk, even if the intentions are pure. I would rather a society that treats its adults like adults and presents the numerical risks reasonably and accurately, instead of one whose public health officials shout out unfounded absolutes, which quickly devolve into medical propaganda.

As I was writing this blog post, I was surprised to find others exploring the same topic. This press release, for example, laments Canadian clinicians’ poor understanding of the true risks associated with unprotected sex and STIs.

I fully expect a public health practitioner to write to me now and tell me what a horrible person am. Here it comes…


Due to the sensitive nature of this post, I thought it best to clarify some things, in response to what was brought up in the comments:

  • It is entirely possible that women who have unprotected sex with men they meet online share common behavioural characteristics that put them in a higher risk group for reasons beyond their “promiscuity”. (I don’t like using such judgment-filled terms, but whatever.) In other words, it’s possible that they’re not sleeping with random Canadian men, but with men who have a higher probability than the average of having an STD; club-goers, for instance, or atypically “promiscuous” men; or single men in general, who have a higher chance of infection than do married men. These women’s risk is therefore possibly orders of magnitude higher than I’ve indicated. But the numbers I’ve presented are based on known data; arguments about a higher risk “promiscuous” population are speculative.
  • I have identified chlamydia as the #1 STD/STI in Canada. This is true, according to the Canadian STI surveillance system. But HPV may have much higher incidence and prevalence.
  • While, according to my analyses above, the risk of contracting an STD is small, the fact remains that there’s a very small –but non-zero– chance of contracting HIV, which can kill you. One can argue that a risk of death is never trivial.
  • The issue boils down to this: knowing how low the actual risk is may end up promoting the risky behaviour. But I’d rather my public health system give me the facts and not rely on fuzzy data and shock tactics to scare me into safe behaviour.

The Misleading Afghan Poll

Quick primer for our readers outside of Canada…. The Canadian military is presently heavily involved in combat operations in Afghanistan, as part of the NATO mission to secure former Taliban-held lands and offer stability in the chaos that resulted after the ill-conceived American invasion. Canadian troops are not (officially) involved in Iraq, so Aghanistan is this country’s major policy excursion in the so-called War on Terror. It’s an unpopular mission –or, more accurately, its popularity is difficult to gauge, since its nature has been miscommunicated to Canadians on many occasions. It’s a combat operation, not a peace-keeping one; and it is being regularly conflated with Canadian health and development aid adventures, as Afghanistan is presently the #1 recipient of Canadian foreign aid. So, supposedly to give some clarity to this issue, the Canadian media commissioned the polling company Environics to survey the Afghan civilian population on their attitudes toward the mission. The results of the study are famously resported on here, with the much quoted excerpt, “60 per cent of Afghans surveyed believe the presence of foreign troops has been good for their country.” Unsurprisingly, the Conservative government, which is a passionate supporter of this mission, is overjoyed at the results. Even Reuters is on board with this interpretation, claiming that “a majority of Afghans support the presence of NATO-led troops and want them to remain in the country to fight the Taliban.” Clearly, this is evidence that the anti-war crowd has been wrong all along, and that Canada’s new militaristic ways are actually a net positivie phenomenon. Right? Well, hold on there, partner. Once more I am disappointed in the West’s journalistic sector, who continue to write articles based on quotations, hyperbole and press releases, rather than on actual source material. A quick visit to the Environics website allows us to examine the company’s summary analysis of the survey, though the actual survey itself remains conspicuously absent. From this summary, it seems that the actual question from which the CBC’s 60% figure is derived does not specifically ask about soldiers or the military. Instead, it asks if the presence of foreign countries on Afghan soil is a good thing; 60% think that yes, it is. But foreign countries is not the same as foreign troops. As mentioned, Afghanistan is the single largest recipient of Canadian development aid. The question conflates (deliberately?) military operations with health, education and development aid. The CBC should be ashamed of falsely reporting that the survey indicates that “60% of Afghans surveyed believe the presence of foreign troops has been good for their country.” It does no such thing. Environics appears to be guilty of a little chicanery, as well. They report that, “a plurality of Afghans say that foreign troops should remain ‘however long it takes to defeat the Taliban and restore order'”, a result jumped on and quoted by the media.

This is true… but the journalists and general public don’t seem to be aware that a “plurality” is not the same as a “majority.” In this case, only 43% reported that they want foreign troops to remain “however long it takes to defeat the Taliban and restore order”. That means that 57% (a true majority) did not give this response. Indeed, the Globe and Mail‘s headline was, “A Majority of Afghans Want Foreign Troops to Stay and Fight.”

This interpretation is by no means suggested by the published results of the Environics poll. The question appears to be broken down a little meaningfully, according to the Environics data which suggest that “foreign presence” is made up of: fighting the Taliban, reconstruction assistance, and training the army and police. In fact, a segment of the Environics summary completely unreported by the media reports that Afghans are only cursorily aware that Canadians are in fact engaged in “fighting the Taliban”. This begs the question, what then do they think Canadians are doing there? Clearly, the answer must be that most Afghans believe the Canadian presence is primarily to provide those non-military services in training and reconstruction. Given this belief, then, of what value –in terms of informing the appropriateness of the Canadian military mission in Afghanistan– is the poll’s conclusion that 60% of Afghans support our “presence”? The answer: there is no value. This study is a complete non-starter and a sham of a public opinion research poll. Thomas Walkom of The Toronto Star notes:

  • “First let us be clear about what the poll did not find. It did not find that a majority of Afghans want foreign troops to stay and fight. It did find that a majority of those polled approved of ‘the presence of foreign countries'”.
  • “[In the poll], India was rated more highly than Canadians… India’s main contribution there is not troops but goods and entrepreneurs.”
  • “In short, the vast majority of Afghans don’t want us to keep fighting in their country until, as Harper puts it, the job is done.”
  • “When Afghans were asked specifically about Canada, most were delightfully complimentary. But first they had to be reminded we were there.”

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