Nursing home outbreaks of invasive group A streptococcal infections - Illinois, Kansas, North Carolina, and Texas

Morbidity and Mortality Weekly Report, August 31, 1990

During the winter of 1989-90, outbreaks of invasive group A streptococcal infections in one nursing home each in Illinois, Kansas, North Carolina, and Texas were reported to CDC. This report summarizes the clinical, laboratory, and epidemiologic features of these outbreaks.

A total of 18 residents had invasive disease, and 10 (56%) died. Clinical features of infection included fever, altered mental status, and symptoms referable to the specific focus of infection. Eight patients had pneumonia with cough and respiratory distress; seven had cutaneous infections (usually at the site of a pre-existing skin lesion); two had sinusitis; and three had no apparent focus for infection. Serious complications included necrotizing fasciitis requiring debridement or amputation, renal failure, and adult respiratory distress syndrome (ARDS). Several patients had illnesses consistent with streptococcal toxic shock-like syndrome [1]. Documented group A streptococcal infection in nursing home staff was rare; two nurses had culture-confirmed pharyngitis, and one, pneumonia.

Isolates from patients from each of the outbreaks were typed as CDC. Two outbreaks were caused by M-nontypeable, T-11/12 strains; one, by M-1, T-1; and one, by M-29, T-nontypeable strains. In all four nursing homes, culture surveys of all residents and staff were performed to evaluate throat and wound carriage of group A streptococci. Eleven (4%) of 312 residents and four (1%) of 297 staff had asymptomatic pharyngeal carriage. At each nursing home, the pharyngeal and invasive isolates were the same serotype. No wound swab cultures were positive.

In one nursing home, a case-control investigation was conducted to determine risk factors for infection. This study suggested person-to-person spread of infection between close contacts, with statistically significant clustering of case-patients by room. No other risk factors were identified.

In three nursing homes, prophylactic antimicrobial therapy was instituted after the survey of residents and staff was completed. In two, full courses of therapy were given to all residents and staff; in the third, therapy was discontinued when all surveillance cultures were reported as negative. In the fourth nursing home, antimicrobial therapy was given only to those who were culture positive. No further cases of infection occurred after these interventions.

Editorial Note: Residents of nursing homes are at increased risk for many infectious diseases. Outbreaks of infection in this setting are facilitated by the close contact of persons who are highly susceptible to infection because of their ages and underlying illnesses. In addition, knowledge of infection-control practices by nursing home personnel and the ability to isolate or cohort patients in a nursing home are often limited [2].

In recent years, invasive group A streptococcal infections have occurred more commonly throughout the United States [1,3]. Recent population-based studies have established an incidence of 4-5 cases per 100,000 persons (CDC, unpublished data). The risk for streptococcal bacteremia and the case-fatality rate are highest in the elderly [4,5]. Additional outbreaks in nursing homes are possible because of the increasing rate of severe group A streptococcal infections, the propensity of this organism to cause disease in the elderly, and the ability of this organism to spread by the person-to-person route.

These four nursing home outbreaks shared several features: 1) a cutaneous or respiratory focus of infection in most patients, 2) high case-fatality rates, 3) uncommon pharyngeal carriage among residents and staff, 4) lack of documentation of carriage in skin lesions not showing evidence of an acute cellulitis, and 5) apparent person-to-person spread between close contacts. Two other reported nursing home outbreaks were characterized by similar features [6,7].

Although specific guidelines for controlling group A streptococcal infections in nursing homes have not been published, the CDC guidelines for isolation precautions in hospitals should be applied to these settings [8]. Isolation of patients until 24 hours of effective antimicrobial therapy has been completed is important. The role of culture surveys and antimicrobial prophylaxis is unclear; because the streptococcal carriage rate is low, treatment of all patients and staff probably is unnecessary. However, throat cultures could be obtained from all nursing home residents and staff followed by institution of antimicrobial therapy; when culture results are available, a course of therapy could be completed only by those who are culture positive or who have symptoms consistent with streptococcal infection. Penicillin is the recommended antimicrobial for treating group A streptococcal infections; erythromycin is recommended for penicillin-allergic persons.

The development of more effective approaches to the control of invasive group A streptococcal infections in nursing home residents and in other settings requires additional information about clusters of this disease. Descriptions of clusters of two or more cases of invasive group A streptococcal infections may be reported to CDC's Respiratory Diseases Branch, Division of Bacterial and Mycotic Diseases, Center for Infectious Diseases, through state health departments. Serotyping of isolates from clusters and case report forms are available from CDC.