NEW YORK (Reuters Health) – In at least two Brazilian cities, microcephaly appears to have been endemic before the start of the Zika virus epidemic, researchers report.
Previous studies have suggested that the prevalence of severe microcephaly at birth is underreported and underestimated.
Using population-based data from the cities of Ribeirao Preto (RP; 7,798 newborns) and Sao Luis (SL; 5,236 hospital births) for the year 2010 – before the Zika virus epidemic – Dr. Antonio A. Silva from Federal University of Maranhao, Sao Luis, and colleagues estimated the baseline prevalence and risk factors for microcephaly at birth. According to INTERGROWTH-21st standards, head circumferences are >2 standard deviations (SDs) below the mean for microcephaly, and >3 SDs below the mean for severe microcephaly.
The findings were reported online January 5 in Pediatrics.
When the last normal menstrual period (LNMP) date was used to estimate gestational age, the prevalence of microcephaly was 3.5% in SL and 3.2% in RP in 2010, nearly 1.5 times the normally expected rates (2.3%).
The estimated prevalence of microcephaly in RP declined to 2.5% when gestational age was based on the LNMP date or obstetrical ultrasonography where available.
Severe microcephaly prevalences were 0.7% in SL and 0.5% in RP – much higher than expected and than previously reported in various national and international studies.
Risk factors associated with microcephaly and severe microcephaly were the same in both cities: low maternal schooling, living without a companion, and intrauterine growth restriction.
Pooled estimates showed that 83,023 cases of microcephaly and 16,605 cases of severe microcephaly would have occurred in Brazil in 2010.
“Our aim in this study was not to make a microcephaly diagnosis but to screen for microcephaly,” the researchers note. “Therefore, newborns with >3 SDs below the mean for gestational age and sex should be referred to neuropediatricians for diagnosis of microcephaly, whereas those between 2 SDs and 3 SDs should be closely monitored by pediatricians or general practitioners, and head circumference should be continuously monitored during early infancy for a definitive diagnosis of microcephaly.”
“A better understanding of microcephaly and the role of Zika virus requires continued population-based, active surveillance and epidemiologic study (as produced here) in the post-Zika era, which can then be followed prospectively to assess trends and understand risk factors,” write Dr. Elizabeth Dufort and Jennifer White from New York State Department of Health, Albany, New York, in a related editorial. “As the world moves on from its intense interest in microcephaly and the Zika virus outbreak, pediatric providers and the public health community must continue to further our understanding of the risks of Zika-associated microcephaly and other birth defects, as well as the causes and preventive interventions of this now-revealed ‘silent endemic of microcephaly.’”
Dr. Anne-Marie Rick from University of Colorado School of Medicine, Anschutz Medical Campus in Aurora, who recently also reported high background rates of congenital microcephaly in rural Guatemala, told Reuters Health by email, “What this study highlights to all healthcare providers, especially those working in low- and middle-income countries, is how much underreporting of microcephaly is happening. The Zika epidemic unveiled this very important problem that could explain why child development in these countries and later school success are impacted.”
“There are at least two important implications,” she said. “The first is that it is very difficult, and probably unnecessary, for countries with limited resources to do testing in all of these infants with small heads. The second is that clinicians and providers need to be educated on how best to apply diagnostic testing to these children if we want to find out beyond Zika what is causing this important finding.”
“Experts and providers around the world need to develop simpler ways to standardize head measurements, particularly when there is uncertainty with gestational age, and to figure out what are the main causes of this finding,” Dr. Rick said. “Investment in this area, as an example, the U.S. NIH Brain Initiative, will help us decipher this puzzle.”
Dr. Silva did not respond to a request for comment.
SOURCES: http://bit.ly/2EconDh and http://bit.ly/2EbpDq3
Pediatrics 2018.
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