Bacteraemia caused by beta-haemolytic streptococci in North Queensland: changing trends over a 14-year period

Abstract

Group A streptococci (GAS) are usually the predominant species in cases of bacteraemia caused by β haemolytic streptococci (BHS). An increasing worldwide incidence of invasive disease from non-group A BHS has been reported. Little is known about the changing trends in invasive disease caused by BHS in Australia. North Queensland has a relatively large indigenous population, who experience significantly higher rates of group A-related disease than the non-indigenous population. This prospective study examined changing trends of disease from large colony BHS that group with A, B, C and G antisera over a 14-year period at the single large tertiary referral hospital in the area. We identified 392 bacteraemic episodes caused by BHS. GAS were most commonly isolated (49%), with adjusted rates remaining stable over the period. There was a significant increase in the incidence of non-neonatal bacteraemia caused by group B streptococci (GBS) over the study period (r = 0.58; p 0.030), largely driven by infection in older, non-indigenous women. Rates of bacteraemia caused by group C streptococci also experienced a modest, but significant, increase over time (r = 0.67; p 0.009). GAS, which had no predominant emm type, were seen most commonly in indigenous subjects (52%). Mortality rates ranged from 3.2% (group G) to 10.3% (group C), with a rate of 7.9% associated with group A disease. The marked rise in GBS disease has been noted worldwide, but the relatively low incidence in indigenous Australian patients has not been described before, despite the burden of well-recognized risk factors for GBS disease within this group.