Contrasting Pediatric and Adult MRSA Isolates
Contrasting Pediatric and Adult MRSA Isolates
We performed a prospective study of all inpatient and outpatient methicillin-resistant Staphylococcus aureus (MRSA) isolates identified at the University of Chicago Hospitals from November 2003 through November 2004. Differences in resistance to non-β-lactam antimicrobial drugs were determined after stratification of the 578 MRSA isolates into 4 groups by patient age (pediatric vs. adult) and onset location (community vs. hospital). Non-β-lactam resistance was significantly greater among the 288 adult than the 177 pediatric community-associated isolates for erythromycin (93.2 vs. 87.0%, p = 0.03), clindamycin (51.8 vs. 7.3%, p<0.001), ciprofloxacin (62.1 vs. 10.7%, p<0.001), gentamicin (11.1 vs. 1.1%, p<0.001), and tetracycline (19.9 vs. 6.4%, p<0.001). In contrast, hospital-associated MRSA isolates from children and adults had similar rates of non-β-lactam antimicrobial drug resistance. In our region, clindamycin is an appropriate empiric therapy of community-associated MRSA infection in children but should be used with caution in adults.
Colonization by and infection with methicillin-resistant Staphylococcus aureus (MRSA) in children and adults who have little or no contact with the healthcare system, phenomena almost unknown before the mid-1990s, have been reported with increasing frequency. In some cities and rural areas, rates of these community-associated MRSA (CA-MRSA) infections, particularly in skin and soft tissue, are increasing rapidly. Many CA-MRSA infections have been attributed to isolates that are distinct from hospital-associated MRSA (HA-MRSA) strains.
The definition of CA-MRSA has not been standardized. No single definition would likely suffice for all purposes. Attempts to define CA-MRSA have focused upon a variety of criteria: temporal (i.e., the MRSA isolate from a specimen is submitted ≈72 hours after hospital admission), host-risk-factor profile (i.e., the patient with the MRSA isolate lacked certain exposure parameters relevant to healthcare facilities, variously defined), antimicrobial drug susceptibility of the MRSA isolates (e.g., susceptibility to clindamycin), and certain molecular aspects of the isolates (e.g., SCCmec type or pulsed-field gel electrophoresis type). Which definition is most important in the choice of empiric antimicrobial drug treatment is not clear. However, a clinician confronted with a putative S. aureus infection needs guidance.
The epidemiology of the emerging CA-MRSA strains, including their origins, reservoirs, modes of dissemination, and effective approaches to their control, is not completely understood. We previously noted that CA-MRSA isolates often lacked resistance to multiple non-β-lactam antimicrobial drugs when compared with HA-MRSA strains. This phenomenon has been documented in adults and children. More recently, we anecdotally observed that children had MRSA infections caused by strains susceptible to non-β-lactam antimicrobial drugs more often than adults. Few data exist that compare antimicrobial drug resistance profiles of adult and pediatric MRSA infection isolates stratified by site of onset (hospital vs. community). Accordingly, using the temporal definition of CA-MRSA, we examined the hypothesis that these 2 groups may be infected by MRSA strains with different rates of resistance to non-β-lactam antimicrobial drugs when the isolates had onset in the community. Therefore, we compared several criteria for the temporal definition of CA-MRSA to assess the impact of changing these criteria on our findings. This article summarizes our study.
We performed a prospective study of all inpatient and outpatient methicillin-resistant Staphylococcus aureus (MRSA) isolates identified at the University of Chicago Hospitals from November 2003 through November 2004. Differences in resistance to non-β-lactam antimicrobial drugs were determined after stratification of the 578 MRSA isolates into 4 groups by patient age (pediatric vs. adult) and onset location (community vs. hospital). Non-β-lactam resistance was significantly greater among the 288 adult than the 177 pediatric community-associated isolates for erythromycin (93.2 vs. 87.0%, p = 0.03), clindamycin (51.8 vs. 7.3%, p<0.001), ciprofloxacin (62.1 vs. 10.7%, p<0.001), gentamicin (11.1 vs. 1.1%, p<0.001), and tetracycline (19.9 vs. 6.4%, p<0.001). In contrast, hospital-associated MRSA isolates from children and adults had similar rates of non-β-lactam antimicrobial drug resistance. In our region, clindamycin is an appropriate empiric therapy of community-associated MRSA infection in children but should be used with caution in adults.
Colonization by and infection with methicillin-resistant Staphylococcus aureus (MRSA) in children and adults who have little or no contact with the healthcare system, phenomena almost unknown before the mid-1990s, have been reported with increasing frequency. In some cities and rural areas, rates of these community-associated MRSA (CA-MRSA) infections, particularly in skin and soft tissue, are increasing rapidly. Many CA-MRSA infections have been attributed to isolates that are distinct from hospital-associated MRSA (HA-MRSA) strains.
The definition of CA-MRSA has not been standardized. No single definition would likely suffice for all purposes. Attempts to define CA-MRSA have focused upon a variety of criteria: temporal (i.e., the MRSA isolate from a specimen is submitted ≈72 hours after hospital admission), host-risk-factor profile (i.e., the patient with the MRSA isolate lacked certain exposure parameters relevant to healthcare facilities, variously defined), antimicrobial drug susceptibility of the MRSA isolates (e.g., susceptibility to clindamycin), and certain molecular aspects of the isolates (e.g., SCCmec type or pulsed-field gel electrophoresis type). Which definition is most important in the choice of empiric antimicrobial drug treatment is not clear. However, a clinician confronted with a putative S. aureus infection needs guidance.
The epidemiology of the emerging CA-MRSA strains, including their origins, reservoirs, modes of dissemination, and effective approaches to their control, is not completely understood. We previously noted that CA-MRSA isolates often lacked resistance to multiple non-β-lactam antimicrobial drugs when compared with HA-MRSA strains. This phenomenon has been documented in adults and children. More recently, we anecdotally observed that children had MRSA infections caused by strains susceptible to non-β-lactam antimicrobial drugs more often than adults. Few data exist that compare antimicrobial drug resistance profiles of adult and pediatric MRSA infection isolates stratified by site of onset (hospital vs. community). Accordingly, using the temporal definition of CA-MRSA, we examined the hypothesis that these 2 groups may be infected by MRSA strains with different rates of resistance to non-β-lactam antimicrobial drugs when the isolates had onset in the community. Therefore, we compared several criteria for the temporal definition of CA-MRSA to assess the impact of changing these criteria on our findings. This article summarizes our study.
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