title: Clinical and epidemiologic features of group a streptococcal pneumonia in Ontario, Canada.
abstract: BACKGROUND
  Since the 1960s, group A streptococcus (GAS) has accounted for less than 1% of cases of community-acquired pneumonia. During the past 2 decades there has been a resurgence of invasive GAS infection, but no large study of GAS pneumonia has been performed.
  
  
  METHODS
  To determine the clinical and epidemiologic features of GAS pneumonia, we conducted prospective, population-based surveillance of all invasive GAS infection in residents of Ontario from January 1, 1992, through December 31, 1999.
  
  
  RESULTS
  Of 2079 cases of invasive GAS infection, 222 (11%) represented GAS pneumonia. The incidence of GAS pneumonia ranged from 0.16 per 100 000 in 1992 to 0.35 per 100 000 in 1999. Most cases were community acquired (81%). Forty-four percent of nursing home-acquired cases occurred during outbreaks. The case fatality rate was 38% for GAS pneumonia, compared with 12% for the entire cohort with invasive GAS infection and 26% for patients with necrotizing fasciitis. The presence of streptococcal toxic shock syndrome (odds ratio, 19; 95% confidence interval, 8.4-42; P =.001) and increasing age (odds ratio per decade, 1.45; 95% confidence interval, 1.2-1.7; P<.001) were associated with fatal outcome. Time to death was rapid, with a median of 2 days despite antimicrobial therapy and supportive measures.
  
  
  CONCLUSIONS
  Group A streptococcal pneumonia is a common form of invasive GAS disease but remains an uncommon cause of community-acquired pneumonia. Progression is rapid despite appropriate therapy. The incidence is similar to, and the case fatality rate higher than, that of necrotizing fasciitis.
authors.affiliation: Department of Microbiology, Mount Sinai Hospital, 600 University Ave, Toronto, Ontario, Canada M5G 1X5.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Muller
authors.forename: Donald E
authors.initials: DE
authors.lastname: Low
authors.forename: Karen A
authors.initials: KA
authors.lastname: Green
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Simor
authors.forename: Mark
authors.initials: M
authors.lastname: Loeb
authors.forename: Daniel
authors.initials: D
authors.lastname: Gregson
authors.forename: Allison
authors.initials: A
authors.lastname: McGeer
mesh_terms: D016009:Chi-Square Distribution; D003428:Cross Infection / Q000453:epidemiology / Q000382:microbiology; D004196:Disease Outbreaks; D019115:Fasciitis, Necrotizing / Q000453:epidemiology / Q000382:microbiology; D017052:Hospital Mortality; D006801:Humans; D015994:Incidence; D009864:Ontario / Q000453:epidemiology; D011014:Pneumonia / Q000453:epidemiology* / Q000382:microbiology*; D011159:Population Surveillance; D012307:Risk Factors; D012772:Shock, Septic / Q000453:epidemiology / Q000382:microbiology; D013290:Streptococcal Infections / Q000453:epidemiology*; D013297:Streptococcus pyogenes / Q000145:classification / Q000302:isolation & purification