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Zika and the Risk of Microcephaly
Michael A. Johansson, Ph.D., Luis Mier-y-Teran-Romero, Ph.D., Jennita Reefhuis, Ph.D., Suzanne M. Gilboa, Ph.D., and Susan L. Hills, M.B., B.S.
May 25, 2016DOI: 10.1056/NEJMp1605367
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Considering different infection-rate scenarios (from 10 to 80%), possible overreporting (0% or 100%), and an uncertain baseline microcephaly rate (2 to 12 cases per 10,000 births), we found a strong association between the risk of microcephaly and infection risk in the first trimester and a negligible association in the second and third trimesters, in keeping with the associations found in population-level estimates for French Polynesia (see the Supplementary Appendix). The estimated baseline risk of microcephaly was low, approximately 2 per 10,000 births (see Panels B, D, and F of the figure, and the Supplementary Appendix), but the estimated risk due to infection in the first trimester ranged from 0.88% (95% credible interval, 0.80 to 0.97), when we assumed an 80% overall ZIKV infection rate and 100% overreporting of microcephaly cases, to 13.2% (95% credible interval, 12.0 to 14.4), when we assumed a 10% ZIKV infection rate and no overreporting.
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Meanwhile, our understanding of the biology of ZIKV infection in pregnancy is based on clinically described cases in pregnant women with symptomatic infection. We therefore have little knowledge of the effects of mild or asymptomatic ZIKV infections or ZIKV infections in early pregnancy, when women may be unaware of the pregnancy. The risk of adverse events may be higher in symptomatic infections, but mild infections are probably more common and thus may also contribute substantially to the overall burden.
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Although much remains unknown about the effects of ZIKV infection during pregnancy, population-level data from French Polynesia and Bahia reveal a clear association between first-trimester ZIKV infection and microcephaly risk. The pattern was probably similar in other parts of northeastern Brazil, where Zika outbreaks in early 2015 were followed by microcephaly outbreaks in late 2015. If the risk of infection and adverse outcomes is similar in the other geographic areas where ZIKV has since spread, many more cases of microcephaly and other adverse outcomes are likely to occur. In light of the growing evidence, it is prudent to take precautions to avoid ZIKV infection during pregnancy5 and for health care systems to prepare for an increased burden of adverse pregnancy outcomes in the coming years.
Full text:
http://www.nejm.org/doi/full/10.1056...=featured_home
Michael A. Johansson, Ph.D., Luis Mier-y-Teran-Romero, Ph.D., Jennita Reefhuis, Ph.D., Suzanne M. Gilboa, Ph.D., and Susan L. Hills, M.B., B.S.
May 25, 2016DOI: 10.1056/NEJMp1605367
Article References Metrics
...
Considering different infection-rate scenarios (from 10 to 80%), possible overreporting (0% or 100%), and an uncertain baseline microcephaly rate (2 to 12 cases per 10,000 births), we found a strong association between the risk of microcephaly and infection risk in the first trimester and a negligible association in the second and third trimesters, in keeping with the associations found in population-level estimates for French Polynesia (see the Supplementary Appendix). The estimated baseline risk of microcephaly was low, approximately 2 per 10,000 births (see Panels B, D, and F of the figure, and the Supplementary Appendix), but the estimated risk due to infection in the first trimester ranged from 0.88% (95% credible interval, 0.80 to 0.97), when we assumed an 80% overall ZIKV infection rate and 100% overreporting of microcephaly cases, to 13.2% (95% credible interval, 12.0 to 14.4), when we assumed a 10% ZIKV infection rate and no overreporting.
...
Meanwhile, our understanding of the biology of ZIKV infection in pregnancy is based on clinically described cases in pregnant women with symptomatic infection. We therefore have little knowledge of the effects of mild or asymptomatic ZIKV infections or ZIKV infections in early pregnancy, when women may be unaware of the pregnancy. The risk of adverse events may be higher in symptomatic infections, but mild infections are probably more common and thus may also contribute substantially to the overall burden.
...
Although much remains unknown about the effects of ZIKV infection during pregnancy, population-level data from French Polynesia and Bahia reveal a clear association between first-trimester ZIKV infection and microcephaly risk. The pattern was probably similar in other parts of northeastern Brazil, where Zika outbreaks in early 2015 were followed by microcephaly outbreaks in late 2015. If the risk of infection and adverse outcomes is similar in the other geographic areas where ZIKV has since spread, many more cases of microcephaly and other adverse outcomes are likely to occur. In light of the growing evidence, it is prudent to take precautions to avoid ZIKV infection during pregnancy5 and for health care systems to prepare for an increased burden of adverse pregnancy outcomes in the coming years.
Full text:
http://www.nejm.org/doi/full/10.1056...=featured_home