Microcephaly in Australian children, 2016-2018: National surveillance study

Objective To describe infants aged <12 months reported with microcephaly to the Australian Paediatric Surveillance Unit (APSU) following emergence of Zika virus infection internationally. Design, setting and patients National, active, monthly surveillance for microcephaly using the APSU. Microcephaly was defined as occipitofrontal circumference (OFC) of more than 2 SDs below the mean for age, gender and gestation. Main outcome measures Clinical spectrum, aetiology and birth prevalence of microcephaly reported by paediatricians. Results Between June 2016 and July 2018, 106 notifications were received, with clinical details provided for 96 (91%). After excluding ineligible notifications, 70 cases were confirmed, giving an annual birth prevalence of 1.12 (95% CI 0.88 to 1.42) per 10 000 live births. Of the total number of cases, 47 (67%) had primary microcephaly (at birth); and 25 (36%) had severe microcephaly (OFC >3 SDs). Birth defects were reported in 42 (60%). Of 49 infants with developmental assessment details available, 25 (51%) had failed to reach all milestones. Vision impairment was reported in 14 (26%). The cause of microcephaly was unknown in 60%: 13 (19%) had been diagnosed with genetic disorders; 22 (39%) had anomalies on neuroimaging. No congenital or probable Zika infection was identified. Severe microcephaly was more often associated with hearing impairment than microcephaly of >2 SDs but ≤3 SDs below the mean (p<0.007). Indigenous children and children with socioeconomic advantage were over-represented among children with microcephaly. Conclusion Novel national data on microcephaly highlight the high proportion of idiopathic cases. This has implications for prevention and management and suggests the need for a standardised diagnostic approach and ongoing surveillance mechanism in Australia.