RECENT TRENDS IN PEDIATRIC HAEMOPHILUS-INFLUENZAE TYPE-B INFECTIONS IN CANADA

Objective: To describe changes in the number of cases of Haemophilus i nfluenzae type b (Hib) infections among Canadian children before and a fter the introductory phases of Hib vaccination. Design: Multicentre c ase series. Setting: All 10 pediatric tertiary care centres across Can ada participating in the Immunization Monitoring Program, Active (IMPA CT) of the Canadian Paediatric Society and the Laboratory Centre for D isease Control. Patients: Children with a Hib infection admitted to an y of the participating hospitals from 1985 to 1994. Annual case totals from 1985 to 1990 were determined from records of hospital laboratori es or coded discharge diagnoses, or both. From 1991 to 1994 intensive case surveillance was conducted on the wards in addition to thorough r ecord searches as above. Outcome measures: Estimated annual case total s for 1985-90. For 1991-94 intensive surveillance for quarterly case t otals, yearly age distribution of cases, and proportion of recent case s that represent vaccination failures or missed opportunities to preve nt infection. Results: The total number of Hib cases from 1985 to 1990 was 2095; from 1991 to 1994, there were 326 laboratory confirmed case s and 15 probable cases supported by Hib antigen detection. The annual number of cases declined from an estimated 485 in 1985 to 24 in 1994, a decrease of 95.1%. The steepest interannual decrease (63.7%) occurr ed between 1992 and 1993, following the introduction of infant-based v accination programs across Canada. The number of Hib cases involving c hildren most at risk (those 6 to 18 months old) decreased from 78 in 1 991 to 4 in 1994. Of the 24 cases in 1994, 6 were categorized as preve ntable, 1 was fatal, and 8 were vaccine failures (2 of which involved currently used vaccines). Conclusion: The prevalence of Hib infections reported by the IMPACT centres has declined greatly since the introdu ction of vaccination programs. However, deaths and complications conti nue to occur, at testing to the need to vaccinate all eligible infants and children against this virulent pathogen.