Invasive haemophilus influenzae and meningococcal infections in Finland. A climatic, epidemiologic and clinical approach.

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 less than 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 (less than 15 years) was 19/100,000; in children less than 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%.