Community-Acquired Methicillin-Resistant Staphylococcus Aureus

Abstract

Source: Gorak EJ, Yamada SM, Brown JD. Community-acquired methicillin-resistant Staphylococcus aureus in hospitalized adults and children without known risk factors. Clin Infect Dis. 1999;29:797–800.Gorak et al report a retrospective chart review of patients with community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections admitted to Honolulu’s Tripler Army Medical Center from 1992 to 1996. Community-acquired MRSA was, by definition, isolated from cultures performed within 48 hours of admission. Patients were excluded from the study if they had been hospitalized within the prior 6 months or transferred from other hospitals or long-term care facilities. Risk factors for community-acquired MRSA infection—recent hospitalization, transfer from another hospital or nursing home, intravenous drug use, prior antimicrobial use and underlying disease—were tabulated as were epidemiologic and clinical data. Of 14 identified hospitalized patients, 6 (43%) were <18 years of age and 10 (71%) had no discernable risk factor for MRSA infection. Skin and soft tissue infections were found in 13 (93%) and pneumonia in one of the patients. Five (36%) of the patients had received antimicrobial therapy in the preceding 2 months. Of the MRSA isolates from infected patients, 100% were susceptible to clindamycin and vancomycin, 86% to erythromycin and 100% to trimethoprim-sulfamethoxazole. All patients recovered after appropriate antimicrobial therapy (in 8) and surgery alone (in 6). The authors conclude that most community-acquired MRSA infections in their population occurred in healthy individuals without known risk factors for MRSA infection.Prior to the introduction of antimicrobials in the 1940s, the mortality of invasive S. aureus infections was approximately 90%. This mortality dramatically declined with the introduction of penicillin G after World War II. Penicillin resistance was noted shortly thereafter and by the 1960s, 90% of community and hospital-acquired S. aureus isolates were penicillin-resistant. Resistance to the penicillinase-resistant penicillins, including methicillin and oxacillin, developed shortly after their introduction in the 1960s. Initially restricted to hospitalized patients, community-acquired MRSA infections have been increasingly reported. Major risk factors (vide supra) have included exposure to patient care facilities and prior antimicrobial therapy. The report of Gorak et al is one of several1,2 documenting MRSA infections in patients with and without known antecedent risk factors. Despite the small number of patients identified, the risk of inadequate therapy and of nosocomial spread make this report of interest for all pediatricians.A few caveats are in order. All of the reports thus far have been retrospective with the inherent shortcomings of such evidence. In the current study, antimicrobial use was sought for only the prior 2 months and in the Herold study1 for 6 months prior to hospitalization. Acquisition and colonization long before the subsequent development of disease requiring hospitalization may have occurred consequent to receiving antimicrobials prior to these time periods or to exposure to individuals with MRSA colonization associated with known risk factors. Although the majority of community-acquired isolates have been sensitive to clindamycin and vancomycin, caution is urged before recommending either of these antibiotics for empiric treatment of patients with community-acquired S. aureus infections. Both clindamycin resistance3 and, even more ominously, reduced susceptibility to vancomycin4 have been described in S. aureus isolates. More discriminate use of all antimicrobials, including semi-synthetic penicillins, may remove much of the selective pressure for the development of antibiotic resistance and reverse the apparent trend toward the development of community-acquired MRSA.