Zika Causes Birth Defects In 1 In 10 Pregnancies

Well … Not really.  But that was the misleading headline of an article I saw in the “healthy living” section of The Huffington Post. And then chased it up to its source — an article published by Reuter‘s journalist Julie Steenhuysen.

There were 3,978,497 births in the US in 2015.  Assuming similar numbers in 2017 (and no seasonal variation which is unlikely), you would be looking at a whopping 400,000 births with a Zika virus related birth defect.  The usual rate of birth defects in the US from all causes is about 3 per 100, so with a cumulative total in excess of three times the current numbers one could anticipate a swift, dramatic (and possibly ineffective) response from the government.

Moving down from the headline, however, a very different story is revealed:

About one in 10 pregnant women with confirmed Zika infections had a fetus or baby with birth defects, offering the clearest picture yet of the risk of Zika infection during pregnancy, U.S. researchers said on Tuesday.

No longer is it 1 in 10 pregnancies. Its 1 in 10 pregnancies with Zika.  The facts are not half as dramatic as the headline.  What am I talking about?  “Not half as dramatic”?  The total number of pregnancies in the US Zika Pregnancy Register for 2016–2017 (on 8 April 2017) was 1,311. Fifty-six of the pregnancies resulted in liveborn infants with birth defects, and 7 of the pregnancies were associated with losses with birth defects.  That just doesn’t sound as impressive a number as the headline suggested.  Undoubtedly personally tragic, but far from as significant a population health issue.