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For weeks, Zika virus has been all over the news. Stark photos of babies with microcephaly, a birth defect in which the infant’s head is abnormally small and its brain often not fully developed, have accompanied stories about the ongoing spread of Zika across more than 20 countries.
The proposed link between Zika and microcephaly began taking shape in September after some pediatricians in northeast Brazil noticed an unusual number of babies born with microcephaly. This spike in microcephaly cases coincided with an outbreak of Zika, a virus related to the dengue virus and spread by mosquitoes.
Given the apparent overlap between microcephaly and Zika virus, “The first impression is that there’s a relationship one to the other,” said Denise Cavalcanti, a geneticist at the State University of Campinas in Campinas, Brazil. First impressions can sometimes deceive, though, and she said the evidence linking the two is circumstantial and not yet confirmed. “We should prove this scientifically.”
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But confirming a link between Zika and microcephaly will take more research and time — months, if not years — and the confirmation may end up as a preponderance of evidence rather than a definitive link. What’s easy to forget about the oft-cited scientific mantra, correlation is not causation, is that causation is incredibly difficult to prove. If you’re a public health official with the job of protecting your community from a scary new threat, you can’t always wait for certainty before you act. And that means you must give advice based on the imperfect evidence you have, rather than the definitive data you wish you had.
Read full, original post: Why It’s So Hard To Prove Zika Is Causing Birth Defects
