Invasive Haemophilus influenzae and Meningococcal Infections in Finland: A Climatic, Epidemiologic and Clinical Approach

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Abstract
A nationwide epidemiological survey on invasive (blood and/or CSF culture positive) Haemophilus influenzae (HI) and meningococcal infections was performed in Finland in 1976-1980. The mean annual incidence of HI infection was 3.4/100 000 inhabitants (813 cases) vs. 2.0/100 000 (469 cases) of meningococcal infection. HI infections showed no geographical predilection, but meningococcal disease, mainly of group B, was more common in northern than in southern Finland (p < 0.005). Meningitis accounted for 61% of the HI and 91% of the meningococcal infections. The overall fatality rates were 3.1% and 7.9%, respectively. Children accounted for 94% of the HI and 59% of the meningococcal cases. The overall annual incidence of bacterial meningitis in children (< 15 years) was 19/100 000; in children < 5 years it was 52/100 000. HI was the most common (62%) causative agent, followed by meningococci (18%) and pneumococci (5%). The fatality rate was 4%. Major neurological sequelae were found in 5%, minor ones in 16%. It was calculated that 42% of the cases of meningitis could have been prevented by vaccines now available on the market. Vaccines now under field investigation may increase the preventability to about 65%.