Incidence of Zika virus-associated birth defects increased by 21% in the latter half of 2016 compared with the first half in geographic areas with local transmission (southern Florida, a portion of south Texas, and Puerto Rico), according to findings published in the January 26 issue of the Morbidity and Mortality Weekly Report.
Augustina Delaney, PhD, from the Division of Congenital and Developmental Disorders, National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, Georgia, and colleagues conducted population-based surveillance for birth defects possibly associated with Zika virus infection from 15 US jurisdictions through 2016, using the US Zika Pregnancy and Infant Registry, which tracks pregnancies with laboratory evidence of infection, and the Zika Birth Defects Surveillance system, which tracks all birth defects potentially related to Zika infection.
Overall, the tracking covered nearly 1 million live births, about a quarter of all live births in the United States and its territories. The geographic areas included certain southern counties of Florida; counties in and around Atlanta, Georgia; Hawaii; Iowa; Illinois; Massachusetts; New Jersey; New York excluding New York City; select regions of North Carolina; Puerto Rico; Rhode Island; South Carolina; certain regions of Texas; Utah; and Vermont.
The areas investigated were classified into three groups: areas with local transmission, areas with higher-prevalence travel-associated Zika virus syndrome (at least one case of confirmed, symptomatic infection per 100,000 residents), and those with lower-prevalence travel-associated Zika virus syndrome (less than one case per 100,000 residents).
The surveillance identified 2962 infants and fetuses with birth defects that could have been related to Zika virus infection (3.0 per 1000 live births; 95% confidence interval [CI], 2.9 – 3.2). Of those, 1457 (49%) had microcephaly or brain abnormalities, 581 (20%) had neural tube defects and other early brain malformations (NTDs), 262 (9%) had isolated eye abnormalities, and 662 (22%) had central nervous system–related problems that were neither brain-related nor ocular. Of the 2962 pregnancies, 2716 (92%) led to live births.
Of the 2962 cases, 2821 had no results from or evidence of having had laboratory testing for Zika infection, 96 tested negative, and 45 tested positive.
Prevalence of birth defects that were possibly Zika-related varied in the three types of areas. In the regions with local Zika transmission, birth defects increased from 2.8 per 1000 live births (182 cases) during the first half of 2016 to 3.0 per 1000 live births (211 cases) in the second half of the year (CI, 2.4 – 3.2 and CI, 2.6 – 3.4, respectively; P = .10).
Inclusion of congenital conditions that may be more common yet rarely linked to the virus, such as NTDs, apparently underestimated virus-associated effects in local transmission jurisdictions, according to the authors. When NTDs were included for these areas, the increase in total birth defects potentially related to infection was not statistically significant.
However, when NTDs were excluded from the analysis, the investigators note a 21% increase, which was statistically significant between the first and second halves of 2016, climbing from 2.0 (CI, 1.7 – 2.4) to 2.4 (CI, 2.1 – 2.8) cases per 1000 live births. This is 29 more cases than expected (P = .009) during the second half of the year, an increase from 140 expected cases to 169 observed cases.
No such changes were detected in areas that did not have local transmission. Specifically, areas with higher travel-related Zika prevalence areas reported 3.0 per 1000 affected live births during the first half of the year (753 cases) and the second half (775 cases). Prevalence fell in areas with lower travel-related Zika, going from 3.4 per 1000 live births (549 cases) during the first half of the year to 3.0 (492 cases) per 1000 live births during the second half (CI, 3.2 – 3.7 and CI, 2.8 – 3.3, respectively; P = .002).
For higher-prevalence areas, excluding NTDs did not change reporting of birth defects during the two halves of the year (2.4 per 1000 live births), and in the lower-prevalence areas, excluding NTDs was associated with a significantly decrease in birth defect prevalence, going from 2.8 (CI, 2.5 – 3.0) to 2.4 (CI, 2.2 – 2.7) per 1000 live births.
“An increase in birth defects potentially related to Zika was only observed in jurisdictions with local Zika virus transmission, and this difference was significant when NTDs were excluded,” the authors write.
They add that surveillance must continue because the peak for birth defects potentially related to Zika virus infection will affect the 2017 birth cohort..
Centers for Disease Control and Prevention Director Brenda Fitzgerald, MD, and colleagues write in a related Viewpoint published online today in JAMA that close attention needs to be paid to children potentially exposed to Zika virus in utero for developmental problems that may manifest after infancy. Even infants born with normal head circumference can develop microcephaly.
“Many infants with congenital Zika virus infection and severe microcephaly will have profound developmental delays and face significant challenges, but ongoing surveillance is needed to determine the extent to which congenitally exposed infants without apparent birth defects will experience similar or other developmental issues,” the Viewpoint authors write.
“Babies with Zika-related birth defects need all the help they can get, as soon as possible and for as long as they need it. This report highlights the critical importance of documenting birth defects possibly related to Zika and our need to maintain vigilance,” Dr Fitzgerald added in a news release.
The researchers and commentators have disclosed no relevant financial relationships.
Morb Mortal Wkly Rep, 2018:67:91-96. Full text
JAMA. Published online January 25, 2018. Full text
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