Population-based surveillance of invasive group A streptococcal disease in British Columbia: 1996 to 1998.

OBJECTIVE

To identify and describe all cases of invasive group A streptococcal (GAS) infection occurring in British Columbia during a two-year period.

DESIGN

Active, laboratory-based surveillance with supplemental case description.

SETTING

Forty community and regional hospitals and the provincial laboratory participated, encompassing all health regions.

POPULATION STUDIED

Entire provincial population from April 1, 1996 to March 31, 1998.

MAIN RESULTS

Over the 24-month surveillance period, 182 eligible cases were identified, yielding a mean annual incidence rate of 2.3/100,000. Patients ranged in age from two to 91 years, with a mean of 39.1 years. Soft tissue infections accounted for 89 of 130 cases (68.5%) with a defined clinical syndrome, 20 of which were necrotizing fasciitis. Injection drug use was described in 55 patients, who, as a group, were younger, more likely to have soft tissue infections and less likely to die of infection than nondrug users. Other risk factors for infection included HIV infection (19 patients); skin damage (26 patients, damage independent of injection drug use); chronic illness (27 patients); and immunosuppresion (three patients). Death from GAS infection occurred in 15 of 131 (11.5%) cases with known outcome, yielding an annual case fatality rate of 1.9/million population. Among necrotizing faciitis cases, the mortality rate was 30%.

CONCLUSIONS

Invasive GAS infections are rare in British Columbia and tend to involve persons with chronic illness or prior skin trauma, especially injection drug abuse, which accounted for nearly half of the cases.