Objective: Identify risk factors for microcephaly and evaluate historical trends of microcephaly and arboviruses to recognize patterns and anomalies that indicate the beginning of the microcephaly epidemic associated with Zika infection.
Methods: The head circumferences of 62,298 newborns was analyzed to identify cases of microcephaly between 2014 and 2017. We compared the groups of newborns with normal head circumferences and those with microcephaly to identify risk factors. A time series with the incidences of microcephaly was analyzed to assess the appearance of anomalous values in order to identify the beginning of the microcephaly epidemic. Data on the incidence of dengue fever was used to develop a control chart, aiming to identify changes in incidence and seasonality that could suggest the circulation of a new arbovirus.
Findings: Premature newborns, children of mothers under 20 years of age and those born in 2014 and 2015 had a higher risk of microcephaly. Three quarters with anomalous incidences of microcephaly were identified, the first in 2014 and the others in 2015. The dengue fever epidemic curve in 2013 shows persistence of high incidences in atypical periods, suggesting the entry of a new virus in the 3rd and 4th quarters.
Conclusions: These findings represent epidemiological evidence of the existence of cases of Zika virus between the 2nd quarter of 2013 and the beginning of 2014. The results add new elements to understanding the Zika virus epidemic in the Americas.