Streptococcal serogroup A epidemic in Norway 1987-1988

A nationwide outbreak of Lancefield group A streptococcal (GAS) infections in Norway during the season 1987-88 is described. Data were collected from the Norwegian infectious disease notification system and supplemented by active search for cases of bacteraemia and other serious infections in addition to serotyping of selected clinical bacterial isolates. The number of reported cases of non-invasive GAS infections from week 29/1987 to week 28/1988 was 60% higher than expected. Between 1 Jan. and 30 June 1988, 84 cases of bacteraemia were notified, several with fulminant septicaemia and shock. The case fatality rate was 25%. Six cases of neonatal GAS septicaemia were seen. There was a nearly 3-fold total increase in occurrence of GAS bacteraemia compared with previous years, and the increase was marked particularly in cases among older children and adults 30-50 years old. Additional culture-confirmed diagnoses included unusual cases compared to recent decades such as pneumonia with empyema, necrotising fasciitis and primary peritonitis. Serotyping of strains collected consecutively from localized infections revealed a marked predominance of T-type 1, opacity factor negative strains (T-1 OF-), ranging from 41% in North Norway to 87% in Mid-Norway. M-typing confirmed that these strains were M-1, as were 87% of the preserved bacteraemia strains from the period described. Although most of the M-1 strains were distinctly mucoid only one case of acute rheumatic fever was reported during the first half of 1988. We conclude that an epidemic of GAS infections caused by M-1 strains has occurred in Norway resulting in an increase in both incidence and seriousness of disease.