Characteristics, risk factors, and outcomes related to Zika virus infection during pregnancy in Northeastern Thailand: A prospective pregnancy cohort study, 2018–2020.

Background: In response to the 2015–2016 Zika virus (ZIKV) outbreak and the causal relationship established between maternal ZIKV infection and adverse infant outcomes, we conducted a cohort study to estimate the incidence of ZIKV infection in pregnancy and assess its impacts in women and infants. Methodology/Principal findings: From May 2018-January 2020, we prospectively followed pregnant women recruited from 134 participating hospitals in two non-adjacent provinces in northeastern Thailand. We collected demographic, clinical, and epidemiologic data and blood and urine at routine antenatal care visits until delivery. ZIKV infections were confirmed by real-time reverse transcriptase polymerase chain reaction (rRT-PCR). Specimens with confirmed ZIKV underwent whole genome sequencing. Among 3,312 women enrolled, 12 (0.36%) had ZIKV infections, of which two (17%) were detected at enrollment. Ten (83%, 3 in 2^nd and 7 in 3^rd trimester) ZIKV infections were detected during study follow-up, resulting in an infection rate of 0.15 per 1,000 person-weeks (95% CI: 0.07–0.28). The majority (11/12, 91.7%) of infections occurred in one province. Persistent ZIKV viremia (42 days) was found in only one woman. Six women with confirmed ZIKV infections were asymptomatic until delivery. Sequencing of 8 ZIKV isolates revealed all were of Asian lineage. All 12 ZIKV infected women gave birth to live, full-term infants; the only observed adverse birth outcome was low birth weight in one (8%) infant. Pregnancies in 3,300 ZIKV-rRT-PCR-negative women were complicated by 101 (3%) fetal deaths, of which 67 (66%) had miscarriages and 34 (34%) had stillbirths. There were no differences between adverse fetal or birth outcomes of live infants born to ZIKV-rRT-PCR-positive mothers compared to live infants born to ZIKV-rRT-PCR-negative mothers. Conclusions/Significance: Confirmed ZIKV infections occurred infrequently in this large pregnancy cohort and observed adverse maternal and birth outcomes did not differ between mothers with and without confirmed infections. Author summary: Zika virus (ZIKV) is an emerging infectious pathogen that was elevated to a Public Health Emergency of International Concern in 2016, due to its possible association with congenital microcephaly, a serious birth defect for infants. We launched a prospective cohort study of pregnant women to look for evidence of ZIKV infection during pregnancy. We enrolled participants in two provinces in northeastern Thailand during May 2018-January 2020. We found a low frequency of ZIKV infection (12/3312, 0.36% by rRT-PCR assay) during the study; two infections were detected at enrollment, while ten were detected later. Six of 12 ZIKV-confirmed women were asymptomatic throughout the study. Most (11/12, 92%) Zika cases occurred in one province. All 12 women with ZIKV delivered normal live births; only one infant had low birth weight and no infants had microcephaly. The eight ZIKV isolates available for whole genome sequencing were of the Asian lineage. At enrollment, the median Dengue virus IgG titer was significantly higher in ZIKV-confirmed than non-ZIKV-confirmed women. Identifying the factors associated with neonatal outcomes after ZIKV exposure in utero would be made easier with additional research studies. [ABSTRACT FROM AUTHOR]