Life-threatening Haemophilus influenzae infections in Scandinavia: a five-country analysis of the incidence and the main clinical and bacteriologic characteristics.

The five countries of Scandinavia (Denmark, Finland, Iceland, Norway, and Sweden) comprise 22.6 million inhabitants and rather homogeneous socioeconomic conditions. A survey of systemic Haemophilus influenzae diseases over the last decades revealed that the reported incidence of H. influenzae disease is increasing. In recent years, the overall incidence has been 3.5 cases per 100,000 people each year (800 cases annually); in children less than 5 years of age, the annual incidence has been 49 cases per 100,000. Meningitis represents only 52% of all systemic H. influenzae diseases, but lack of reliable data may obscure the importance of other entities. Few strains (less than 5%) are beta-lactamase-positive, and the case fatality rate is 3%. Analysis of seasonal variation shows peaks in June and September-October. If the efficacy of the H. influenzae conjugate vaccines were as high as that of a conjugate vaccine used in Finland during 1986-1987 (approximately 85% efficacy), then at least an 80% reduction in life-threatening H. influenzae infections would be achieved annually by routine immunization before or at the age of 6 months.