Zika virus infection estimates, Mexico

Area of Science:

• Epidemiology
• Infectious Diseases
• Public Health

Background:

• Zika virus infection poses a significant public health threat, particularly to pregnant women and their developing fetuses.
• Understanding the true scale of Zika virus epidemics is crucial for effective public health response and resource allocation.
• Congenital microcephaly is a serious birth defect associated with maternal Zika virus infection.

Purpose of the Study:

• To determine the actual magnitude of the Zika virus epidemic in Mexico.
• To assess the association between Zika virus infection and the risk of microcephaly in Mexico.
• To analyze geographical and altitudinal factors influencing Zika virus transmission and microcephaly risk.

Main Methods:

• Estimated symptomatic Zika virus infections by analyzing reported cases and birth rates in Mexico (November 2015 - August 2016).
• Compared monthly incidences of congenital microcephaly before and after Zika virus introduction using birth certificate data (January 2010 - September 2017).
• Utilized Poisson interrupted time series, statistical modeling, and graphical analyses, stratifying by maternal altitude (≥2200m).

Main Results:

• Estimated symptomatic Zika cases (60,172) were 7.3 times higher than reported cases.
• A significant 2.9-fold increase in microcephaly incidence was observed post-Zika introduction (IRR: 2.9; 95% CI: 2.3-3.6).
• Babies born to mothers at altitudes below 2200m showed a higher microcephaly risk (IRR: 3.4; 95% CI: 2.9-3.9).

Conclusions:

• The Zika virus epidemic in Mexico was substantially underestimated by laboratory-confirmed case counts.
• Zika virus infection is significantly associated with an increased risk of microcephaly.
• Altitude is a critical factor, with lower altitudes showing a greater risk of microcephaly associated with Zika virus.