Invasive Haemophilus influenzae infections in children in Kamikawa subprefecture, Hokkaido, Japan, 1996-2005, before the introduction of H. influenzae type b vaccination

We evaluated 52 children with invasive Haemophilus influenzae infection in Kamikawa subprefucture, Hokkaido, Japan between 1996 and 2005. The most frequent disease was meningitis, in 30 children (57.7%), followed by pneumonia in 9 (17.3%), bacteremia in 8 (15.4%), epiglottitis in 4 (7.7%), and cellulitis in 1 (1.9%). Patients ranged in age from 0 days to 8 years. Thirty (57.7%) of the patients were less than 2 years old. Only 6 cases of invasive H. influenzae infection occurred in children older than 5 years. Between 1996 and 2005 the annual incidence rates of invasive H. influenzae infection in children aged less than 5 years, and those aged from 5 to 9 years were 4.3/100 000 to 56.8/100 000 and 0/100 000 to 12.4/100 000, respectively. A marked increase of the annual incidence rate in children aged under 5 years was observed in the most recent 2 years (2004 and 2005). No patients with invasive H. influenzae infection died, but sequelae were seen at discharge in 2 patients with meningitis, predominantly epilepsy and developmental delay of varying severity. Two patients with epiglottitis were treated by endotracheal intubation or tracheostomy. Of 41 strains isolated from 1999 to 2005, 35 were classified for antimicrobial resistance by the polymerase chain reaction (PCR) method. The number of strains of β-lactamase-negative ampicillin-susceptible, low β-lactamase-negative ampicillin-resistant, β-lactamase-negative ampicillin-resistant, β-lactamase-negative amoxicillin/clavulanic acid resistant-I, and β-lactamase-positive amoxicillin/clavulanic acid resistant-II, were 22, 3, 5, 2, and 3, respectively. The serotype in 37 (97.4%) of 38 cases demonstrated type b.