Baseline microcephaly prevalence in rural Guatemala: implications for neonatal screening for congenital Zika virus infection

Abstract

Abstract Background Microcephaly is the result of disturbance in early brain development and has various causes. Zika was identified in Central America in early 2015. Establishing baseline microcephaly rates in areas affected by Zika is important for the assessment of the burden and contribution of Zika to microcephaly in low-resource settings. Methods We undertook a retrospective review of records from a community wellness programme in rural Guatemala where trained community health workers obtained data on weight, length, and head circumference for infants aged 0 to 13 days, enrolled in the programme between August 1, 2014, and March 31, 2016. We estimated gestational age using a Z-score of zero for length on the modified Fenton growth curve. Z-scores for head circumference and weight, adjusted for gestational age and sex, were then calculated. We used univariate logistic regression to test associations between microcephaly and low weight (Z ≤−1), small size for gestational age (weight below 10th percentile for gestational age), and sex. We analysed head circumference Z-scores and microcephaly for changes over time using birth month as well as multiple time-breaks (we compared infants born before versus after April 30, 2015; October 31, 2015; and January 31, 2016) with Student t-tests, and logistic and linear regression. Findings We included 296 infants: mean head circumference Z-score was −0·68 (95% CI −0·78 to −0·58). 20 infants (6·8%) had a head circumference Z-score ≤–2 and were considered to have microcephaly, giving a microcephaly prevalence of 676 per 10 000 livebirths. One infant (0·3%) had a head circumference Z-score ≤–3. Weight ≤–1 SD (OR 4·59 (1·69–12·41, p=0·003) and small for gestational age (6·65, 1·88–23·55, p=0·003) were associated with microcephaly. Sex was not significantly associated with microcephaly. Birth month and time-breaks were not associated with microcephaly nor with head circumference Z score. Interpretation Baseline neonatal microcephaly present in this rural Guatemalan community before and during Guatemala's early Zika epidemic is more than 100 and 300 times higher than baseline rates reported before the Zika virus epidemic in Puerto Rico and Brazil, respectively. Increased microcephaly rate associated with Zika epidemics in other countries was not detectable in our study population, probably because data were collected early in the Zika epidemic. High baseline microcephaly rates have important implications for neonatal screening programmes to identify infants congenitally infected with Zika in low-income countries. Funding The Center for Global Health at the University of Colorado and the Jose Fernando Bolanos Menendez Foundation provided funding for the wellness programme.