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Updated: Aug 21, 2026
Subcutaneous Infection of Methicillin Resistant Staphylococcus Aureus (MRSA)
Published on: February 9, 2011
Methicillin-resistant Staphylococcus aureus (MRSA) nares colonization at hospital admission and its effect on
Kepler A Davis1, Justin J Stewart, Helen K Crouch
1Infectious Disease Service, Brooke Army Medical Center, Ft. Sam Houston, Texas 78234-6000, USA. kepler.davis@amedd.army.mil
Background:
Asymptomatic colonization with methicillin-resistant Staphylococcus aureus (MRSA) has been described as a risk factor for subsequent MRSA infection. MRSA is an important nosocomial pathogen but has currently been reported in patients without typical risk factors for nosocomial acquisition. This study was designed to evaluate the impact of asymptomatic nares MRSA colonization on the development of subsequent MRSA infection. The incidence of MRSA infection was examined in patients with and patients without MRSA or methicillin-susceptible S. aureus (MSSA) colonization at admission to the hospital and in those who developed colonization during hospitalization.
Methods:
Patients admitted to 5 representative hospital units were prospectively evaluated. Nares samples were obtained for culture at admission and during hospitalization. Laboratory culture results were monitored to identify all MRSA infections that occurred during the study period and 1 year thereafter.
Results:
Of the 758 patients who had cultures of nares samples performed at admission, 3.4% were colonized with MRSA, and 21% were colonized with MSSA. A total of 19% of patients with MRSA colonization at admission and 25% who acquired MRSA colonization during hospitalization developed infection with MRSA, compared with 1.5% and 2.0% of patients colonized with MSSA (P<.01) and uncolonized (P<.01), respectively, at admission. MRSA colonization at admission increased the risk of subsequent MRSA infection, compared with MSSA colonization (relative risk [RR], 13; 95% confidence interval [CI], 2.7-64) or no staphylococcal colonization (RR, 9.5; 95% CI, 3.6-25) at admission. Acquisition of MRSA colonization also increased the risk for subsequent MRSA infection, compared with no acquisition (RR, 12; 95% CI, 4.0-38).
Conclusion:
MRSA colonization of nares, either present at admission to the hospital or acquired during hospitalization, increases the risk for MRSA infection. Identifying MRSA colonization at admission could target a high-risk population that may benefit from interventions to decrease the risk for subsequent MRSA infection.
Insights
Asymptomatic nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA) significantly increases the risk of developing MRSA infection. Identifying MRSA carriers upon hospital admission can help target high-risk patients for preventative interventions.
Area of Science:
- Infectious Diseases
- Clinical Microbiology
- Epidemiology
Background:
- Asymptomatic colonization with methicillin-resistant Staphylococcus aureus (MRSA) is a known risk factor for subsequent MRSA infections.
- MRSA is a critical nosocomial pathogen, frequently identified in patients lacking typical risk factors for hospital-acquired infections.
Purpose of the Study:
- To evaluate the impact of asymptomatic nasal MRSA colonization on the development of subsequent MRSA infections.
- To compare MRSA infection incidence in patients with and without MRSA or methicillin-susceptible S. aureus (MSSA) colonization at hospital admission and during hospitalization.
Main Methods:
- Prospective evaluation of patients admitted to 5 hospital units.
- Nasal samples cultured at admission and during hospitalization.
- Monitoring of laboratory culture results for MRSA infections during the study period and one year post-study.
Main Results:
- 3.4% of patients were colonized with MRSA and 21% with MSSA upon admission.
- 19% of patients with admission MRSA colonization and 25% who acquired MRSA during hospitalization developed MRSA infection.
- MRSA colonization at admission (RR, 9.5-13) and acquisition during hospitalization (RR, 12) significantly increased the risk of subsequent MRSA infection compared to MSSA or no staphylococcal colonization.
Conclusions:
- Nasal MRSA colonization, whether present at admission or acquired during hospitalization, elevates the risk of MRSA infection.
- Identifying MRSA colonization at hospital admission can pinpoint high-risk individuals who may benefit from targeted interventions to reduce infection risk.
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