Invasive infections caused by Haemophilus influenzae serotypes in twelve Canadian IMPACT centers, 1996-2001

Background: Haemophilus influenzae type b (Hib) immunization has changed the epidemiology of pediatric bacterial invasive disease. We describe the epidemiology of H. influenzae invasive infections in 12 Canadian pediatric tertiary care [Immunization Monitoring Program, ACTive (IMPACT)] centers during the era of universal immunization against this pathogen. Methods: Children with positive cultures for H. influenzae sero-types a to f (Hia to Hit) and nontypable H. influenzae from sterile sites were identified from the laboratory records at 12 IMPACT centers from January 1, 1996 to December 31, 2001. Hospital records were retrospectively reviewed for demographic and clinical information. Results: Of 166 H. influenzae cases, 58 (35%) were caused by Hib, 89 (54%) by non-b serotypes, and 19 (11%) were not scrotyped. The non-b serotypes included: 25 Hia (28%), 4 Hid (4%), 2 Hie (2%), 11 Hif (12%), and 47 were nontypable isolates (53%). For patients with Hib and Hia infection, meningitis was the most common presentation, accounting for 40% and 52% respectively, whereas the most common presentation for nontypable serotypes was pneumonia, seen in 43% of cases. Epiglottitis was associated mainly with Hib. Aboriginal ethnicity was an important risk factor for Hia cases, accounting for 76% of patients with infections caused by this serotype. Mean duration of hospitalization, need for admission to a pediatric intensive care unit, and case fatality rates were similar for the cases because of Hib, Hia, Hif, and nontypable serotypes. Conclusions: In 1996-2001, two-thirds of H. influenzae invasive disease in the 12 IMPACT centers was caused by non-b serotypes, which were associated with significant morbidity and mortality.