Microcephaly Risk High When Infected Early in Pregnancy

A report published by the CDC on December 9, 2016, offered important new evidence about the geographic breadth, impact, and timing of Zika virus disease and microcephaly (a smaller than expected infant head size).


The CDC’s preliminary report on Zika virus disease and microcephaly in Colombia demonstrates that an increase in microcephaly is not specific to Brazil. This finding confirms that countries with Zika virus outbreaks are likely to experience large increases in microcephaly and other Zika-related birth defects. The report also suggests that Zika virus infection in the first months of pregnancy poses the greatest risk of microcephaly.


Zika virus infection during pregnancy can cause microcephaly and serious brain abnormalities in fetuses and infants exposed in utero. The Zika virus disease outbreak in the World Health Organization’s Region of the Americas began in Brazil, which first reported a laboratory-confirmed Zika virus outbreak in May 2015. Colombia confirmed local transmission of Zika virus about 5 months later, in October 2015. Colombia’s Instituto Nacional de Salud (INS) maintains national surveillance for birth defects, including microcephaly.


Colombia has experienced a four-fold increase overall in microcephaly following the Zika virus outbreak in 2016. From January 31 through mid-November 2016, there were 476 cases of microcephaly reported in Colombia; this represents more than a four-fold increase from the same period in 2015, with a nine-fold increase in July 2016 (the peak month) compared with July 2015. Of the 476 cases with microcephaly, 432 were live-born infants and 44 were pregnancy losses.


According to the report, the peak in cases of microcephaly in Colombia came approximately six months after the period in which the highest number of new Zika infections was reported, which suggests that the highest risk period for Zika-associated microcephaly is likely to be in the first half of pregnancy, particularly the first trimester and early in the second. The temporal association between Zika virus infections and microcephaly, with the peak of reported microcephaly occurring approximately 24 weeks after the peak of the Zika outbreak, provides evidence that the greatest risk period is likely the first trimester of pregnancy and early in the second trimester of pregnancy. The CDC recommends that women take steps to protect themselves during the entire pregnancy.


In general, Colombia reported approximately 105,000 cases of Zika virus disease, including nearly 20,000 cases in pregnant women, from August 9, 2015, through November 26, 2016. Zika virus infection during pregnancy can cause microcephaly and other brain abnormalities in babies.


The CDC and Colombia’s INS continue their collaboration to investigate microcephaly and other birth defects. This collaboration will provide critical information about Zika virus infection during pregnancy, including the range of health effects and the effect of other factors on pregnancy outcomes.


See the CDC Announcement


See the CDC Report


See also Medical Law Perspectives, May 2016 Report: Vectors of Risk: Zika, West Nile, and Similar Tick and Mosquito Disease Litigation