Zika and the Risk of Microcephaly

Abstract

Relationship between Trimester-Specific ZIKV Infection Risk and Microcephaly in Bahia, Brazil. Panel A shows the approximate number of suspected Zika cases reported in Bahia by month. Panel B shows the estimated ZIKV infection rate, assuming an overall infection rate of 10 to 80%. Panel C shows the numbers of microcephaly cases in Bahia including reported cases (green) and estimated additional cases (yellow), accounting for reporting delays (see Supplementary Appendix). Horizontal lines indicate the approximate gestational period by trimester for births in October 2015 through February 2016 assuming the pregnancies reached full term. In the remaining panels, the solid points represent the total number of microcephaly cases for each birth cohort (July 2015–February 2016) in Bahia (adjusted for reporting delays) relative to the estimated infection rate for the first (Panel D), second (Panel E), and third (Panel F) trimesters if the overall 2015 infection rate was 50%. The open points represent 50% of this value (reflecting potential overreporting), and the grey area represents expected baseline microcephaly rates of 2 to 12 cases per 10,000 births. Model-fitted estimates and 95% credible intervals for microcephaly cases are shown for data with (dot-dashed) and without overreporting (dashed).