Experience in diagnosing congenital Zika syndrome in Brazilian children born to asymptomatic mothers

Introduction: Typical symptoms of primary Zika virus infection are not specific and share similarities with other arbovirus infections such as dengue fever and chikungunya. As acute infection can be asymptomatic in up to 73% of cases, infants with microcephaly represent a diagnostic challenge for pediatricians. We describe the frequency of congenital Zika syndrome (CZS) in Brazilian children born to asymptomatic pregnant mothers and its differential diagnosis. Methods: This longitudinal, observational study was conducted on children with suspected CZS whose mothers did not report rash during pregnancy, referred to the reference hospital in a metropolitan area of Rio de Janeiro, Brazil. The diagnosis of suspected CZS was based on Brazilian Ministry of Health protocol. Results: Forty-three (17%) of 246 referred children were born to mothers without rash history during pregnancy. Thirteen (30%) of 43 children met the Brazilian Ministry of Health criteria for CZS, all with microcephaly (two post-natal). The other children included 11 cases with post-natal microcephaly due to hypoxic-ischemic encephalopathy (6), non-progressive encephalopathy of unknown etiology (2), microcephaly under investigation (2) and congenital toxoplasmosis (1); 17 children were misdiagnosed with microcephaly and progressed with normal head circumference during the follow-up period; one child was included because of epidemiological link and one was loss to follow-up. All children who underwent laboratory investigation for ZIKV infection during neonatal period had negative RT-qPCR tests. Conclusion: We emphasize the increasing importance of CZS in differential diagnosis of microcephaly at birth or post-natal period. Detailed clinical investigation assisted by neuroimaging tests may clarify the diagnosis of CZS when laboratory tests are not available during the acute phase of the disease.