Reporting of birth defects from the Zika outbreak in Colombia, 2015-2017

Objective. The Zika outbreak affected several tropical countries in 2015 and 2016, requiring the creation of intensified surveillance strategies for microcephaly and other neurological syndromes. The effect of the Zika outbreak on the reporting of birth defects in Colombia was evaluated from the perspective of the national surveillance system. Methods. National reporting of newborns with different birth defects was analyzed; variations in reporting attributed to the epidemic were determined through difference in differences (DID), a semiparametric model. Results. During the period of study, 18,234 cases of birth defects were reported in Colombia. The majority were congenital malformations (91.9%), and 82.3% was confirmed by clinical diagnosis or epidemiological link. In the case of microcephaly, eight new cases per epidemiological week were reported (coefficient of case reporting [D] = 8.8; P = 0.000) and 32 cases from other congenital anatomical malformations (D = 32.0; P= 0.000). The absolute value of the difference in differences estimator attributed to the Zika outbreak increased weekly case reporting of microcephaly (DID = vertical bar-5.0 vertical bar; P= 0.008) and congenital malformations (DID = vertical bar-12.0 vertical bar; P= 0.111). Conclusions. The Zika outbreak increased reporting of newborns with microcephaly, but caused no significant variation in reporting of other malformations and functional birth defects of sensory or metabolic origin in the surveillance system.