A COMPARISON OF 2 PERTUSSIS EPIDEMICS IN AUCKLAND

Aim. To determine if the addition of the 6 week dose of pertussis vacc ine in 1984 was associated with any change in the hospitalisation rate for children with pertussis and the higher hospitalisation rates for Maori and Pacific Islander children with pertussis. Methods. Design: P opulation based study of pertussis hospitalisations using a retrospect ive chart review of hospitalisation data for children during the 1991 epidemic, which was compared to previously published data from the 198 2 epidemic. Setting: Princess Mary and Middlemore hospitals, Auckland. Subjects: Children aged 0-14 years resident in metropolitan Auckland and hospitalised in Auckland during 1982 or 1991 with pertussis. Measu rements: Hospitalisation rates were calculated as number of children w ith a discharge diagnosis of pertussis per 1000 children aged 0-14 yea rs based on 1981 and 1991 census data. 1982 data were converted to per son-years as published report was for an 8 month period. Hospitalisati on rates were compared as a relative risk. (RR) of hospitalisation in 1991 versus 1982. Results. There were 84 cases during 8 months in 1982 and 66 cases in 1991. Rates of hospitalisation by ethnic group; in 19 82 were 0.24 Other/European (OE), 1.98 Maori (M), 1.37 Pacific Islande r (PI); and in 1991 were 0.22 OE, 0.51 M, 0.40 PI. Compared to 1982 th e relative risk of hospitalisation in 1991 adjusted for ethnicity was 0.43 (CI 0.33, 0.58, p<0.0001). Compared to 1982 there was a significa nt reduction in the hospitalisation rate in 1991 for M (RR = 0.26, CI 0.16, 0.43, p<0.0001); and PI children (RR = 0.29, CI 0.16, 0.54, p<0. 0001); but not for OE children (RR = 0.91, 95% CI 0.57, 1.46, p=0.70). Conclusions. There was a significant reduction in the rate of hospita lisation for pertussis in 1991 compared to 1982. This reduction in hos pitalisation rate was due to a reduction in rates for Maori and Pacifi c Islander children.