Group A streptococci (Streptococcus pyogenes) are the most common bacterial cause of pharyngitis and a frequent cause of cutaneous infections including impetigo and cellulitis. More rarely, group A streptococci are implicated as the etiologic agent in patients with pneumonia, bacteremia, and a newly described toxic shock-like syndrome.' While invasive group A streptococcal infections occur in persons of all ages, the incidence of these infections is greatest in the elderly, as is the case/fatality ratio. Factors that may contribute to the increased risk of invasive group A streptococcal infections in the elderly include a higher prevalence of underlying illnesses and, possibly, decreased levels of antibodies directed against the group A streptococcal M-protein, a major determinant of virulence.

From the advent of the antibiotic era until the mid-1980s, the occurrence of severe group A streptococcal infections declined. However, since 1985, rheumatic fever outbreaks in civilian and military populations, a syndrome designated the streptococcal toxic shock-like syndrome, and an increased incidence of group A streptococcal bacteremia have been reported. These changes in the epidemiology of group A streptococcal infections have been associated with changes in the serotype distribution, with an increasing proportion of invasive infections caused by M-1 and M-3 strains, and an increase in the proportion of organisms producing pyrogenic exotoxin A, which has been linked to the toxic shock-like syndrome.

Although the incidence of infection related to arterial catheterization was recently reported to be low in one pediatric intensive care unit,' nosocomial infection associated with the use of intravascular pressure monitoring devices, including arterial and central venous pressure catheters, may be overlooked. These infections may be manifested by persistent bacteremia with unusual, often water-related, gram-negative organisms (e.g., Pseudomonas, Klebsiella, Enterobacter, Serratia, or Flavobacterium species).

Group A Streptococcus has been identified as the cause of several outbreaks of infection in residents of nursing homes. These reports described outbreaks that included persons with severe invasive disease as well as more limited infection. The purpose of this report is to describe an investigation of two consecutive outbreaks of group A Streptococcus that occurred in a single nursing home, where all affected residents had disease of mild to moderate disease severity. This report focuses on the identification of risk factors for infection and describes the approach used to control the spread of infection in the nursing home.