Purpose To estimate the minimum incidence of congenital Zika syndrome (CZS) and severe microcephaly in Canada and describe key clinical, epidemiological, aetiological and outcome features of these conditions.
Methods Two separate national surveillance studies were conducted on CZS and severe microcephaly using the well-established Canadian Paediatric Surveillance Program from 2016 to 2019. Over 2700 paediatricians across Canada were surveyed monthly and asked to report demographic details, pregnancy and travel history, infant anthropometry, clinical features and laboratory findings of newly identified cases. Reports were reviewed to assign an underlying aetiology of severe microcephaly. Incidence rates were estimated using monthly live birth denominators.
Results Thirty-four infants met the case definition for severe microcephaly and <5 met the case definition for CZS. The associated minimum incidence rates were 4.5 per 100 000 live births for severe microcephaly and 0.1–0.5 per 100 000 live births for CZS. Of severe microcephaly cases, 53% were attributed to genetic causes, 15% to infectious or ischaemic causes and 32% to unknown causes. The median head circumference-for-age Z-score at birth was −3.2 (IQR −3.8 to −2.6), and catch-up growth was often not achieved. Common clinical features included intracranial abnormalities (n=23), dysmorphology (n=19) and developmental delays (n=14). Mothers of infants with non-genetic aetiologies travelled during pregnancy more often (10/16) than mothers of infants with genetic aetiologies (<5/18; p<0.01).
Conclusion Severe microcephaly and CZS are both rare in Canada. Minimum incidence rates can be used as a baseline against which novel or re-emergent causes of severe microcephaly or CZS can be compared.
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Contributors SKM, MO, AB, SPM, CMH, CRMN and JT conceptualised and designed the CZS study. CRMN, AB, SPM, CMH, SKM, MS, JAE and JT conceptualised and designed the severe microcephaly study. DSF performed the data analysis. SKM and DSF drafted the initial manuscript. All authors reviewed and approved the final manuscript.
Funding This study received funding from the Public Health Agency of Canada, through the CPSP.
Competing interests None declared.
Patient consent for publication Obtained.
Ethics approval The Hospital for Sick Children Research Ethics Board, IDs 1000054799 (severe microcephaly) and 1000056359 (congenital Zika syndrome. Public Health Agency of Canada Research Ethics Board, IDs 2016-0002 (severe microcephaly) and 2016-0029 (congenital Zika syndrome).
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data may be obtained from a third party and are not publicly available. The data presented within this manuscript are bound by confidentiality and data stewardship policies of the CPSP, a joint programme of the Canadian Paediatric Society and the Public Health Agency of Canada. In accordance with relevant federal and provincial health privacy legislation, the policies are strictly enforced to prevent identification of patients. The study protocols and case report forms can be found at https://www.cpsp.cps.ca/surveillance/study-etude/congenital-zika-syndrome-in-infants-in-canada and https://www.cpsp.cps.ca/surveillance/study-etude/severe-microcephaly.
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