Validation of Prevalence of Congenital Microcephaly — New York City, 2013–2015

BACKGROUND: Congenital Zika virus (ZIKV) infection can cause microcephaly and other fetal neurological anomalies. Though national prevalence estimates of microcephaly range from 2–12 per 10,000 live births, the historical prevalence of microcephaly in New York City (NYC) is unknown. We used retrospective chart review to establish a validated baseline prevalence estimate of severe congenital microcephaly in NYC for 2013–2015, prior to ZIKV importation. A secondary objective was to assess for disparities in prevalence of severe congenital microcephaly.

METHODS: We sent requests to all 44 NYC birth hospitals to identify NYC newborns diagnosed with microcephaly during 2013–2015; all hospitals responded and 37 (84%) identified cases. We reviewed and classified the infant cases using the National Birth Defects Prevention Network case definition for severe congenital microcephaly, defined as a head circumference <3^rd percentile for gestational age and sex. We abstracted demographic information, diagnoses, and maternal factors from infant charts and obtained maternal race/ethnicity data from birth certificates. We geocoded newborn addresses to assign census tract-based poverty (categorized as: low, <10% of residents living below the federal poverty level (FPL); medium, 10%–<20% below FPL; high, 20%–<30% below FPL; and very high, ≥30% below FPL). At least 10% of charts underwent review by two clinicians.

RESULTS : Birth hospitals identified 294 cases, of which 157 (53%) met the case definition for severe congenital microcephaly, a prevalence of 4.7 per 10,000 live births. Of the charts that underwent review by two clinicians, a Cohen’s kappa of 0.91 was obtained. Among newborns with severe congenital microcephaly, 16 (10%) had a congenital or perinatal infection and 14 (9%) consumed alcohol, drugs, tobacco or a teratogenic medication during pregnancy. Prevalence was elevated in the Bronx (9.7/10,000 live births) compared to other NYC boroughs (3.6/10,000 live births), among those who live in very high poverty areas (7.2/10,000 live births) compared to those in low poverty areas (2.7/10,000 live births), and among mothers who were Non-Hispanic black (7.6/10,000 live births) or Hispanic (6.3/10,000 live births) compared to Non-Hispanic white mothers (2.3/10,000 live births).

CONCLUSIONS : We calculated baseline severe congenital microcephaly prevalence in NYC against which prospective surveillance can be compared. Prevalence was elevated in the Bronx, among racial and ethnic minorities, and among those living in high poverty areas. Disparities in microcephaly prevalence underscore the importance of conducting future public health surveillance and outreach for congenital ZIKV syndrome in vulnerable populations and the facilities that serve them.