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637: Microcephaly in the era of the Zika virus: diagnostic criteria needed

      Objective

      CDC guidelines endorse evaluation of an infant for possible congenital Zika virus infection in the setting of microcephaly, defined as head circumference (HC) less than the third percentile or out of proportion to body size. However, this latter criterion is not well defined. We sought to determine rates of microcephaly in newborns using different diagnostic criteria.

      Study Design

      Retrospective database review of all newborns admitted to an academic medical center from 9/3/2007 to 3/8/2016 for whom there was recorded data of gestational age, weight, length, HC, and gender. Percentiles were calculated using the Fenton bulk research calculator. A cut off of 1.2 was used to define HC/weight disproportion (HCWD). 1.2 is the equivalent of HC 3% / weight 25%. Diagnosis codes were obtained from electronic medical records.

      Results

      28,886 newborns met inclusion criteria. 3.1% had a HC< 3%tile based on Fenton standards. (Female: 3.5%; Male: 2.6%; Preterm: 3.2%; Full-term: 2.6%). However, only 40 (0.1%) had a discharge diagnosis of microcephaly. 2.8% of the total population met criteria for HCWD. Notably, 34% of those with the discharge diagnosis of microcephaly had HCWD. All HCs in this group were < 15th percentile. Of those with the diagnosis of microcephaly, 15% had abnormal head imaging, 2.5% were diagnosed with a potential infectious etiology of microcephaly (CMV), 65% did not require neurologic follow-up, and 40% were full term newborns who were discharged with only routine follow-up.

      Conclusion

      Microcephaly is an uncommon diagnosis without clear diagnostic criteria. Congenital infection is associated with a small percentage of microcephalic infants. The vast majority of infants with small HC do not have HCWD. As awareness of microcephaly increases due to discussions of Zika virus, we risk overdiagnosis of infants without clinically significant findings. Additional studies are needed to determine which features of newborns require further workup and to establish clear diagnostic criteria for microcephaly.