Association between Zika virus and microcephaly in French Polynesia, 2013-15: a retrospective study
Simon Cauchemez1, Marianne Besnard2, Priscillia Bompard3
1Mathematical Modelling of Infectious Diseases, Institut Pasteur, Paris, France.
Background:
The emergence of Zika virus in the Americas has coincided with increased reports of babies born with microcephaly. On Feb 1, 2016, WHO declared the suspected link between Zika virus and microcephaly to be a Public Health Emergency of International Concern. This association, however, has not been precisely quantified.
Methods:
We retrospectively analysed data from a Zika virus outbreak in French Polynesia, which was the largest documented outbreak before that in the Americas. We used serological and surveillance data to estimate the probability of infection with Zika virus for each week of the epidemic and searched medical records to identify all cases of microcephaly from September, 2013, to July, 2015. Simple models were used to assess periods of risk in pregnancy when Zika virus might increase the risk of microcephaly and estimate the associated risk.
Findings:
The Zika virus outbreak began in October, 2013, and ended in April, 2014, and 66% (95% CI 62-70) of the general population were infected. Of the eight microcephaly cases identified during the 23-month study period, seven (88%) occurred in the 4-month period March 1 to July 10, 2014. The timing of these cases was best explained by a period of risk in the first trimester of pregnancy. In this model, the baseline prevalence of microcephaly was two cases (95% CI 0-8) per 10,000 neonates, and the risk of microcephaly associated with Zika virus infection was 95 cases (34-191) per 10,000 women infected in the first trimester. We could not rule out an increased risk of microcephaly from infection in other trimesters, but models that excluded the first trimester were not supported by the data.
Interpretation:
Our findings provide a quantitative estimate of the risk of microcephaly in fetuses and neonates whose mothers are infected with Zika virus.
Funding:
Labex-IBEID, NIH-MIDAS, AXA Research fund, EU-PREDEMICS.
Insights
Zika virus infection during early pregnancy significantly increases microcephaly risk. This study quantifies the risk for pregnant women exposed to Zika virus, providing crucial data for public health.
Area of Science:
- Epidemiology
- Virology
- Public Health
Background:
- Zika virus emergence in the Americas linked to increased microcephaly reports.
- World Health Organization declared Zika virus and microcephaly link a Public Health Emergency of International Concern.
- The precise quantitative risk association between Zika virus infection and microcephaly remained undetermined.
Purpose of the Study:
- To retrospectively analyze data from a large Zika virus outbreak in French Polynesia.
- To estimate the probability of Zika virus infection during the epidemic.
- To quantify the risk of microcephaly associated with maternal Zika virus infection during pregnancy.
Main Methods:
- Retrospective analysis of serological and surveillance data from a French Polynesia Zika virus outbreak (Oct 2013–Apr 2014).
- Medical record review to identify microcephaly cases between September 2013 and July 2015.
- Utilized simple models to determine periods of risk during pregnancy and estimate associated microcephaly risk.
Main Results:
- The Zika virus outbreak infected 66% of the population; eight microcephaly cases were identified.
- Seven of eight microcephaly cases occurred between March 1 and July 10, 2014, indicating a first-trimester risk period.
- Estimated risk: 95 (34–191) additional microcephaly cases per 10,000 women infected in the first trimester, with a baseline of 2 per 10,000 neonates.
Conclusions:
- Findings provide a quantitative estimate of microcephaly risk in fetuses and neonates following maternal Zika virus infection.
- The first trimester of pregnancy is identified as a critical period of risk for Zika virus-associated microcephaly.
- The study underscores the significant impact of Zika virus on fetal development and the need for continued public health vigilance.
