Invasive Haemophilus influenzae type b disease in Sweden 1997-2003: epidemiological trends and patterns in the post-vaccine era.

The introduction of vaccination against Haemophilus influenzae serotype b (Hib) in the Swedish childhood vaccination programme in 1992 resulted in a rapid 90% decline in meningitis cases. A recent rise in incidence in the UK underlines the need for continuing surveillance also in Sweden. Descriptive analysis of surveillance data for all invasive Hib infection cases notified in 1997-2003 was performed, with respect to age, gender, seasonality, geography and death; 185 cases (children 0-4 y: 37 cases) of invasive Hib disease were reported for an average incidence rate of 0.3 per 100,000 (children 0-4 y; 1.1). One fifth of the cases were children below 5 y of age, but two- thirds were over 30 y; median age was 49.5 y of age. 61% were female and 39% male (p = 0.0026). The sharp downward trend in incidence seen in the period 1993-1998 appears to have halted. During 2002 and 2003 there was a slight increase for children aged 0-4 y. There was also a highly significant female dominance, which has not been described before. Together with a shift in age distribution towards adults this points to women aged +30 y as a potential new risk group. This may reflect an increased risk owing to women being the primary carers of young children.