Zika virus (ZIKV) is a flavivirus that was recently introduced into Brazil. Brasil et al. enrolled pregnant women in whom a rash had developed within the previous 5 days and tested blood and urine specimens for ZIKV by reverse-transcriptase–polymerase-chain-reaction assays. The authors followed women prospectively to obtain data on pregnancy and infant outcomes. This final report updates preliminary data on Zika virus infection among pregnant women in Rio de Janeiro. ZIKV infection during pregnancy was associated with fetal death, fetal growth restriction, and central nervous system abnormalities in a new Original Article.
• Are there any clinical features that may be more common among ZIKV-positive women than ZIKV-negative women?
In the study by Brasil et al., a descending macular or maculopapular rash was the most common type of exanthem noted in ZIKV-positive women. The maculopapular rash was seen far more frequently in ZIKV-positive women than in ZIKV-negative women (P=0.02). The other prevalent finding was pruritus, which was seen in 90% of ZIKV-positive women in the study. Conjunctival injection was present in 58% of ZIKV-positive women and in a smaller percentage (40%) of ZIKV-negative women (P=0.03), which suggests that this symptom is a more specific clinical feature of ZIKV infection.
• Does the time window for adverse outcomes in utero due to Zika virus infection occur only in early pregnancy?
With rubella, the time window for adverse outcomes in utero occurs in the first 16 weeks of pregnancy. In contrast, with ZIKV, the time window appears to be throughout pregnancy. ZIKV pathogenicity was evident in the Brasil study cohort even in the presence of a “control” group that was affected by chikungunya virus, which is also linked to adverse pregnancy outcomes, particularly fetal loss. Adverse outcomes after ZIKV infection occurred regardless of the timing of maternal infection; adverse outcomes occurred in 55% of pregnancies in which the mother was infected in the first trimester (11 of 20 ZIKV-infected pregnancies), in 52% of those in which the mother was infected in the second trimester (37 of 71 ZIKV-infected pregnancies), and in 29% of those in which the mother was infected in the last trimester of pregnancy (10 of 34 ZIKV-infected pregnancies).
Morning Report Questions
Q: How did pregnancy outcomes compare between ZIKV-positive and ZIKV-negative women in the study by Brasil et al.?
A: Despite the high rate of adverse outcomes in the control group of pregnant women with other infectious illnesses, the findings in the ZIKV-positive group were far more striking. Among 125 pregnancies in ZIKV-positive women, 58 adverse pregnancy outcomes were noted (46.4%); in contrast, 7 of the 61 pregnancies (11.5%) in the ZIKV-negative cohort resulted in adverse outcomes (P<0.001). Among 117 live births in the ZIKV-positive cohort, 49 infants (42%) were found to have abnormalities on clinical examination, imaging, or both; in contrast, among 57 live births in the ZIKV-negative cohort, 3 infants (5%) had such abnormalities (P<0.001). ZIKV-positive women were nearly 10 times as likely as ZIKV-negative women to have emergency cesarean sections performed owing to fetal distress (23.5% vs. 2.5%, P=0.003). Infants born to ZIKV-positive mothers were also nearly four times as likely to need critical care assistance immediately after birth (a finding that is reflective of fetal distress) as infants who had not been exposed to ZIKV (21% vs. 6%, P=0.01). There was no significant difference in the rate of fetal loss between ZIKV-positive mothers and ZIKV-negative mothers (7.2% and 6.6%, respectively; P=1.0).
Q: Was microcephaly the most common abnormality observed after ZIKV infection in the study by Brasil et al.?
A: Four infants in the ZIKV-positive group (3.4%) were noted to have microcephaly at birth; two were small-for-gestational-age infants with proportionate microcephaly (i.e., the head size is small but is proportional to the weight and length of the infant), and two had disproportionate microcephaly (i.e., the head size is small relative to the weight and length of the infant). None of the infants in the control group had microcephaly. Although microcephaly has been widely discussed in relation to ZIKV infection, it is important to note that other findings such as cerebral calcifications and fetal growth restriction were present more frequently.