Anecdotes, Data, Case Reports, and Sex

Last week, I blogged briefly about a report of an unusual cluster of Zika virus infections. Like a lot of scientists, I got a good chuckle out of Martin Enserink’s reporting on the story for Science, and figured that if people wanted the full analysis they could read the freely available primary report.

In the ensuing days, the popular media picked up the story and might have taken it a little too seriously, as my friend and fellow TWiV host Vincent Racaniello explains over at Virology Blog. Vincent’s objection echoes the sentiments I’m hearing from other scientists as well: the news coverage sounds as if this proves that Zika virus is sexually transmitted, a claim the paper doesn’t quite back up.

It’s a valid complaint, but it misses some important points. While it’s true that anecdote is not data, there is nonetheless an established and legitimate tradition for this sort of publication in the scientific literature. It’s called a case report, and it’s the basis of much of modern medicine. Consider this publication from 1982. Not much to it, really, just a note about some odd diseases in a cohort of homosexual men in California. These patients could have some common risk factor for an unknown immune disorder, or it could just be a really bizarre coincidence. By itself, the report proves nothing, only that these cases might deserve a closer look. When researchers did look closer, they found AIDS.

I’m not saying Zika virus has that kind of potential, only that we shouldn’t dismiss case reports as “anecdotes.” The difference is that while an anecdote is a purely personal story, a peer-reviewed case report is a medically and scientifically rigorous analysis of such a story. Foy et al. were right to report their experiences, which do strongly suggest that Zika virus could be transmitted sexually. Of course there are other possibilities. The point of a case report isn’t to prove etiology beyond all doubt, it’s to redefine the limits of the possible. Previously, we didn’t know this might happen. Now we should try to see if it really does.

As for the press coverage, I’m not convinced it’s been so horrible either. Consider the story on Fox News, a source not normally known for its evidence-based reporting. While the headline is certainly sensational and definitive-sounding, the story itself quotes the original paper accurately:

According to Foy’s study, the circumstantial evidence for [Zika virus] sexual transmission is strong. “Patients 1 and 3 reported having vaginal sexual intercourse in the days after patient 1 returned home but before the onset of his clinical illness,” he wrote. Foy said there are hints in other literature that sexually transmitted mosquito-borne viruses are possible. Boars who were infected with Japanese encephalitis shed the virus in their semen, and when female pigs were artificially inseminated with the boars’ semen they also became infected.

Indeed, the circumstantial evidence is strong. Now someone should try to get some less circumstantial evidence.

Meanwhile, science just got a big shot of free publicity. Adventurous expeditions. Sex. Deadly diseases. Sex. New scientific discoveries. And did I mention sex? Kids, does that sound like the kind of career you’d like to pursue? I thought so.

Scientists should certainly maintain their skepticism when talking to the press, and the press could certainly use a bit more skepticism of its own with reports like this, but let’s pick our battles. From what I’ve seen, the mainstream media coverage of this story has focused mainly on the novelty of the virus and, of course, the sex. It sells, you know. I suspect that six months from now, the general public will remember only a vague outline of this report, if anything. What effect would that have? For starters, it might make people think twice about having unprotected sex. They might also get some general idea that even obscure, exotic diseases can travel rapidly and unpredictably. Those seem like good take-home lessons to me.

Foy, B. (2011). Probable Non–Vector-borne Transmission of Zika Virus, Colorado, USA Emerging Infectious Diseases DOI: 10.3201/eid1705.101939