5.6.1: In Real Life- A Case-Controlled Study
In 2015 there was an outbreak of infants born in Brazil with microcephaly, a devastating condition characterized by an abnormally small head size and severe brain damage. This condition is typically rare, which led researchers to hypothesize that it was related in some way to a Zika virus infection in the mothers during pregnancy. There had been an outbreak in northeastern Brazil of the Zika virus, which is mostly transmitted via mosquitos, but can also be transmitted sexually and from mother to fetus ( Zika Virus , 2014). The researchers recruited 91 cases (babies born with microcephaly) and 173 controls (babies without microcephaly, born around the same time), and then investigated their exposure to the Zika virus. What the researchers found was a strong association between a Zika infection during pregnancy and microcephaly: 32 of the 91 cases were Zika positive, and 0 of the 173 controls had contracted the disease. The researchers also noted that Zika tests often produce a false negative, so it is likely that many more of the mothers whose babies were born with microcephaly had indeed contracted the virus during pregnancy (Schneider, 2020, p. 63).