Intussusception After Monovalent Human Rotavirus Vaccine in Australia Severity and Comparison of Using Healthcare Database Records Versus Case Confirmation to Assess Risk

Background: Surveillance for intussusception (IS) has been recommended in countries using rotavirus vaccine, but can be resource intensive. There is little data about the relative severity of rotavirus vaccine-associated IS compared with other IS cases. We collected detailed clinical data on all cases to evaluate the validity of ICD coding for IS in routinely collected data and case severity. Methods: Hospitalizations and emergency department presentations coded as IS in infants aged <12 months from July 1, 2007, to June 30, 2010, were classified using Brighton criteria by case note review. We used self-controlled case series analysis to estimate IS risk after vaccination for all and only Brighton level 1 cases. Results: Of 179 unique episodes coded as IS, 110 (61%) met Brighton level 1 criteria; self-controlled case series analysis found a relative incidence of IS in days 1-7 after the first dose of RV1 of 11.1 (95% confidence interval: 2.6-48.0). When all coded episodes of IS were included, relative incidence was 4.0 (95% confidence interval: 1.3-12.7). The proportion of Brighton 1 cases requiring surgery was 39% for those within 21 days of vaccine receipt and 34% for others (P = 0.67). Conclusions: Using ICD-coded cases without individual confirmation yielded a lower point estimate of risk for IS post rotavirus vaccination; however, the risk remained statistically compatible with that for chart confirmed cases only. Analysis using healthcare databases to evaluate risk of IS if conducted without case confirmation may be insufficient to confirm a low-level risk. IS episodes after vaccination were not more severe.