Epidemiology of intussusception in New Zealand pre-rotavirus vaccination.

Aims: To describe the epidemiology of intussusception in New Zealand children aged 0-36 months prior to the introduction of routine rotavirus vaccination.

Methods: ICD-10 coding data from the New Zealand National Minimum Data Set (NMDS) was used to identify all cases of intussusception in children aged 0-36 months between January 1998 and December 2013. These data were linked with birth data from the New Zealand census. Population incidence rates of intussusception were calculated, and demographic characteristics described.

Results: Over the 16-year study period, there were 794 cases of intussusception. The majority (56%) occurred in the first year of life (age adjusted incidence rate 56.1/100,000 child-years, 95% confidence interval (CI) 41.7-71.2). Intussusception occurred more frequently in males (36.4/100,000 (95% CI 24.6-48.2) versus 19.5/100,000 (95% CI 10.8-28.1, p<0.001)). There was no difference in intussusception incidence between ethnic groups, although cases occurred at a younger age in Māori and Pacific infants compared to Asian and other ethnicities (Pacific median 7.5 months (interquartile range 5.9-11.6), Māori 7.8 months (IQR 5.5-12.3), European 9.2 months (IQR 5.8-15.8), Other Ethnicity 10.2 months (IQR 8.2-12.3), Asian 10.5 months (IQR 7.0-17.1 )). There was a weak seasonal trend with incidence troughs in January and July, and corresponding peaks in March and September. There was wide variation in presentation rates across District Health Board (DHB) regions, with a national average of 18.0/100,000 child-years (95% CI 9.7-26.3). Most patients were admitted on a single occasion to a single hospital for treatment (81%).

Conclusions: This study updates background incidence rates of intussusception prior to the introduction of a national rotavirus vaccination programme in July 2014. It identifies a trend of earlier intussusception in Māori and Pacific infants; the relationship between earlier intussusception and the risk of vaccine-associated events is unknown.