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Updated: Jul 8, 2026
Development and Assessment of Intracellular Infection Models for Staphylococcus aureus
Published on: January 17, 2025
Importance of bacterial burden among methicillin-resistant Staphylococcus aureus carriers in a long-term care
Nimalie D Stone1, Donna R Lewis, H K Lowery
1Emory University School of Medicine, Emory University, Atlanta, Georgia, USA. nstone@emory.edu
Objective:
To evaluate the prevalence and transmission of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization, as well as risk factors associated with MRSA carriage, among residents of a long-term care facility (LTCF).
Design:
Prospective, longitudinal cohort study.
Setting:
A 100-bed Veterans Administration LTCF.
Participants:
All current and newly admitted residents of the LTCF during an 8-week study period.
Methods:
Nasal swab samples were obtained weekly and cultured on MRSA-selective media, and the cultures were graded for growth on a semiquantitative scale from 0 (no growth) to 6 (heavy growth). Epidemiologic data for the periods before and during the study were collected to assess risk factors for MRSA carriage.
Results:
Of 83 LTCF residents, 49 (59%) had 1 or more nasal swab cultures that were positive for MRSA; 34 (41%) were consistently culture-negative (designated "noncarriers"). Of the 49 culture-positive residents, 30 (36% of the total of 83 residents) had all cultures positive for MRSA (designated "persistent carriers"), and 19 (23% of the 83 residents) had at least 1 culture, but not all cultures, positive for MRSA (designated "intermittent carriers"). Multivariate analysis showed that participants with at least 1 nasal swab culture positive for MRSA were likely to have had previous hospitalization (odds ratio, 3.9) or wounds (odds ratio, 8.2). Persistent carriers and intermittent carriers did not differ in epidemiologic characteristics but did differ in mean MRSA growth score (3.7 vs 0.7; P<.001).
Conclusions:
Epidemiologic characteristics differed between noncarriers and subjects with at least 1 nasal swab culture positive for MRSA. However, in this LTCF population, only the degree of bacterial colonization (as reflected by mean MRSA growth score) distinguished persistent carriers from intermittent carriers. Understanding the burden of colonization may be important when determining future surveillance and control strategies.
Insights
Methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization affects 59% of long-term care facility residents. Previous hospitalization and wounds are key risk factors for MRSA carriage, with colonization burden distinguishing persistent from intermittent carriers.
Area of Science:
- Infectious Diseases
- Epidemiology
- Healthcare-Associated Infections
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen in healthcare settings.
- Long-term care facilities (LTCFs) are vulnerable environments for MRSA transmission.
- Understanding MRSA colonization dynamics in LTCF residents is crucial for infection control.
Purpose of the Study:
- To determine the prevalence of MRSA nasal colonization in LTCF residents.
- To identify risk factors associated with MRSA carriage.
- To investigate MRSA transmission patterns within the facility.
Main Methods:
- Prospective, longitudinal cohort study conducted over 8 weeks in a 100-bed VA LTCF.
- Weekly nasal swab cultures analyzed for MRSA growth on a semiquantitative scale (0-6).
- Collection of epidemiologic data to assess risk factors for MRSA carriage.
Main Results:
- 59% (49/83) of residents exhibited MRSA nasal colonization.
- Previous hospitalization (OR, 3.9) and presence of wounds (OR, 8.2) were significant risk factors.
- Persistent MRSA carriers showed significantly higher mean MRSA growth scores compared to intermittent carriers (3.7 vs 0.7).
Conclusions:
- Epidemiologic factors differentiated MRSA carriers from non-carriers.
- The degree of MRSA colonization, not epidemiologic characteristics, distinguished persistent from intermittent carriers.
- Colonization burden is a key consideration for future MRSA surveillance and control strategies in LTCFs.
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