In this Update we review the results of 4 recent investigations that have important implications:
- the first analysis of the US Zika Virus Infection in Pregnancy Registry
- a study revealing an improved antibiotic regimen to prevent postcesarean infection
- an important new methodology for reducing the rate of perinatal transmission of hepatitis B virus (HBV) infection
- the risks and benefits of combination antiretroviral therapy (ART) in pregnancy.
Zika virus-associated birth defect rates similar regardless of symptom presence; first-trimester exposure has highest rate of anomalies
Honein MA, Dawson AL, Petersen EE, et al; US Zika Pregnancy Registry Collaboration. Birth defects among fetuses and infants of US women with evidence of possible Zika virus infection during pregnancy. JAMA. 2017;317(1):59-68.
Honein and colleagues provide a summary of the data from the US Zika Virus in Pregnancy Registry (a collaboration between the Centers for Disease Control and Prevention and state and local health departments), estimating the proportion of fetuses and infants with birth defects based on maternal symptoms of Zika virus infection and trimester of possible infection.
Related article:
Zika virus: Counseling considerations for this emerging perinatal threat
Details of the study
The authors evaluated the outcomes of 442 women who had laboratory evidence of a possible Zika virus infection during pregnancy. Overall, 26 infants (6%; 95% confidence interval (CI), 4%-8%) had evidence of birth defects related to the Zika virus. Of note, abnormalities were detected in 16 of the 271 children (6%; 95% CI, 4%-9%) born to women who were asymptomatic and 10 of 167 (6%; 95% CI, 3%-11%) children delivered to women with symptomatic infections.
The most common birth defect was microcephaly, although other serious central nervous system abnormalities were noted as well. Nine of 85 women (11%; 95% CI, 6%-19%) who had exposure only during the first trimester had infants with birth defects. There were no documented abnormalities in infants born to mothers who developed Zika virus infection only in the second or third trimester.
Related article:
Zika virus update: A rapidly moving target
Key study findings
This article is important for several reasons. First, the authors describe the largest series of pregnant women in the United States with Zika virus infection. All of these patients developed Zika virus infection as a result of foreign travel or exposure to sexual partners who had traveled to Zika virus endemic areas. Second, the authors confirmed findings that previously had been based only on mathematical models rather than on actual case series. Specifically, they demonstrated that the risk of a serious birth defect following first-trimester exposure to Zika virus infection was approximately 11%, with a 95% CI that extended from 6% to 19%. Finally, Honein and colleagues highlighted the key fact that the risk of a serious birth defect was comparable in mothers who had either an asymptomatic or a symptomatic infection, a finding that seems somewhat counterintuitive.
WHAT THIS EVIDENCE MEANS FOR PRACTICE
This study's critical observations are a "call to action" for clinicians who provide prenatal care.1,2 Proactive steps include:
- For patients considering pregnancy, strongly advise against travel to any area of the world where Zika virus is endemic until an effective vaccine is available to protect against this infection.
- For any woman with a newly diagnosed pregnancy, ask about travel to an endemic area.
- Inquire also about a pregnant woman's exposure to partners who live in, or who have traveled to, areas of the world where Zika virus infection is endemic.
- Be aware that both asymptomatic and symptomatic infection in the first trimester of pregnancy pose a grave risk to the fetus.
- Recognize that, although microcephaly is the principal abnormality associated with Zika virus infection, other central nervous system anomalies also may occur in these children. These include ventriculomegaly, subcortical calcifications, abnormalities of the corpus callosum, cerebral atrophy, and cerebellar abnormalities. In addition, infected infants may have arthrogryposis.
- Finally, as Honein and colleagues noted, laboratory testing for Zika virus infection is imperfect. In the early stages of infection or exposure, testing for Zika virus infection by polymerase chain reaction (PCR) in both serum and urine is the preferred test. After a period of 2 weeks, the preferred laboratory test is an immunoglobulin M (IgM) assay. Positive tests on the IgM assay must be confirmed by the plaque neutralization reduction test--a very important test for differentiating Zika virus infection from infection caused by other arboviruses, such as those that cause dengue fever and chikungunya.