Five new confirmed microcephaly cases in Colombia may be harbingers of epidemic

A recent report by the New England Complex Systems Institute (NECSI) noted that, despite their supposed connection, cases of microcephaly were not rising in sync with Zika's epidemic spread. Of all the countries reporting cases, only Brazil has reported a distinctively large number of birth defects. In Colombia, a study of 12,000 pregnant, Zika-infected women reported in the New England Journal of Medicine had not shown any cases of microcephaly. The cases of microcephaly reported from outside the study could be explained by the background rate of microcephaly from unrelated causes.

The new report from Colombia states that there are a total of 11 confirmed cases of microcephaly with Zika infections until June 18, five more than the number confirmed as of the previous week. The previous confirmed case, the sixth, was confirmed four weeks earlier. According to the NECSI analysis, it and the five other reported cases of microcephaly with Zika infections were consistent with the random co-occurence of each of them separately, and therefore should not be attributed to Zika as the cause.

The five new confirmed Zika and microcephaly cases provide the best evidence available for an impending microcephaly epidemic in Colombia. In an updated report released today, NECSI points out that given the timing and number of Zika-affected pregnancies, the total can be expected to rise to 200 microcephaly cases in the next few months. This means the rate of such births should rise dramatically, reaching over 10 microcephaly and Zika births each week, well above the background rate.

Whether or not Zika and microcephaly are linked will be conclusively determined from reports over the next few weeks.