Evolving epidemiologic characteristics of invasive group a streptococcal disease in Utah, 2002-2010.

Background: Invasive group A Streptococcus (GAS) infections are associated with substantial morbidity and mortality. Recent national surveillance data report stable rates of invasive GAS disease, although these may not capture geographic variation.

Methods: We performed a population-based, retrospective laboratory surveillance study of invasive GAS disease among Utah residents from 2002-2010. We used Intermountain Healthcare's electronic medical records and data warehouse to identify patients from whom GAS was isolated by culture. We defined clinical syndromes of invasive GAS disease on the basis of International Classification of Diseases, Ninth Revision codes. We abstracted demographic information, comorbidities, and microbiologic and laboratory findings.

Results: From 2002-2010, we identified 1514 cases of invasive GAS disease among Utah residents. The estimated mean annual incidence rate was 6.3 cases/100,000 persons, which was higher than the national rate of 3.6 cases/100,000 (P < .01). The incidence of invasive GAS disease in Utah rose from 3.5 cases/100,000 persons in 2002 to 9.8 cases/100,000 persons in 2010 (P = .01). Among children aged <18 years, the incidence of invasive GAS increased from 3.0 cases/100,000 children in 2002 to 14.1 cases/100,000 children in 2010 (P < .01). The increase in the pediatric population was due, in part, to an increase in GAS pneumonia (P = .047). The rate of invasive GAS disease in adults aged 18-64 years increased from 3.4 cases/100 000 persons in 2002 to 7.6 cases/100,000 persons in 2010 (P = .02). Rates among those aged ≥65 years were stable. The incidence of acute rheumatic fever declined from 6.1 to 3.7 cases/100,000 (P = .04).

Conclusions: The epidemiologic characteristics of invasive GAS disease in Utah has changed substantially over the past decade, including a significant increase in the overall incidence of invasive disease-driven primarily by increasing disease in younger persons-that coincided temporally with a decrease in the incidence of acute rheumatic fever.