Estimating the Number of Pregnant Women Infected With Zika Virus and Expected Infants With Microcephaly Following the Zika Virus Outbreak in Puerto Rico, 2016 | Congenital Defects | JAMA Pediatrics | JAMA Network
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    1 Comment for this article
    Important topic, statistical method needs work though
    Roberto Rivera | University of Puerto Rico, Mayaguez
    The authors tackle an important topic. Although there now exists strong evidence that Zika causes congenital defects, there is a lot of uncertainty on rates of defects caused by the virus. I do find some issues with the paper though:
    - Zika is also sexually transmitted. The paper does not take this into consideration and appears to make no mention of it.
    - IQR is not an interval, it is the difference of two quartiles, one number.
    - There are several Monte Carlo procedures. The supplement provides information about the distributions but not about what Monte Carlo procedure was used, burn-in period chosen, or whether
    convergence was attained. Bayesian methods are very flexible but can be sensitive to choice of priors (informative or non-informative).
    - The statistical procedure allows for the construction of credible sets (the Bayesian analog of confidence intervals). These intervals are much more informative than just providing the median, first and third quartile. Assuming the first and third quartile values given (wrongfully called IQR) are the posterior distribution quartiles, then the interval provided is a 50% Bayesian confidence interval, instead of the common 95 or 99% interval used. Thus, the cases of microcephaly due to Zika may potentially be much lower, or much higher than the limits in the paper (i.e. there's a 25% chance that the number of cases is above the third quartile)
    - Microcephaly is just one congenital defect. In the end what is really needed is a credible interval for congenital defects, not just microcephaly. At the very least this should have been mentioned.
    Original Investigation
    October 2016

    Estimating the Number of Pregnant Women Infected With Zika Virus and Expected Infants With Microcephaly Following the Zika Virus Outbreak in Puerto Rico, 2016

    Author Affiliations
    • 1Centers for Disease Control and Prevention, Atlanta, Georgia
    • 2University of Georgia, Athens
    • 3Carter Consulting Inc, Atlanta, Georgia
    • 4Puerto Rico Department of Health, San Juan, Puerto Rico
    JAMA Pediatr. 2016;170(10):940-945. doi:10.1001/jamapediatrics.2016.2974

    Importance  Zika virus (ZIKV) infection during pregnancy is a cause of congenital microcephaly and severe fetal brain defects, and it has been associated with other adverse pregnancy and birth outcomes.

    Objective  To estimate the number of pregnant women infected with ZIKV in Puerto Rico and the number of associated congenital microcephaly cases.

    Design, Setting, and Participants  We conducted a modeling study from April to July 2016. Using parameters derived from published reports, outcomes were modeled probabilistically using Monte Carlo simulation. We used uncertainty distributions to reflect the limited information available for parameter values. Given the high level of uncertainty in model parameters, interquartile ranges (IQRs) are presented as primary results. Outcomes were modeled for pregnant women in Puerto Rico, which currently has more confirmed ZIKV cases than any other US location.

    Exposure  Zika virus infection in pregnant women.

    Main Outcomes and Measures  Number of pregnant women infected with ZIKV and number of congenital microcephaly cases.

    Results  We estimated an IQR of 5900 to 10 300 pregnant women (median, 7800) might be infected during the initial ZIKV outbreak in Puerto Rico. Of these, an IQR of 100 to 270 infants (median, 180) may be born with microcephaly due to congenital ZIKV infection from mid-2016 to mid-2017. In the absence of a ZIKV outbreak, an IQR of 9 to 16 cases (median, 12) of congenital microcephaly are expected in Puerto Rico per year.

    Conclusions and Relevance  The estimate of 5900 to 10 300 pregnant women that might be infected with ZIKV provides an estimate for the number of infants that could potentially have ZIKV-associated adverse outcomes. Including baseline cases of microcephaly, we estimated that an IQR of 110 to 290 total cases of congenital microcephaly, mostly attributable to ZIKV infection, could occur from mid-2016 to mid-2017 in the absence of effective interventions. The primary limitation in this analysis is uncertainty in model parameters. Multivariate sensitivity analyses indicated that the cumulative incidence of ZIKV infection and risk of microcephaly given maternal infection in the first trimester were the primary drivers of both magnitude and uncertainty in the estimated number of microcephaly cases. Increased information on these parameters would lead to more precise estimates. Nonetheless, the results underscore the need for urgent actions being undertaken in Puerto Rico to prevent congenital ZIKV infection and prepare for affected infants.