Methicillin-Resistant Staphylococcus aureus (MRSA) Nasal Real-Time PCR: A Predictive Tool for Contamination of the Hospital Environment

Abstract

Introduction We sought to determine whether the bacterial burden in the nares, as determined by the cycle threshold (CT) value from real-time MRSA PCR, is predictive of environmental contamination with MRSA. Methods Patients identified as MRSA nasal carriers per hospital protocol were enrolled within 72 hours of room admission. Patients were excluded if 1) nasal mupirocin or chlorhexidine body-wash was used within the past month or 2) an active MRSA infection was suspected. Four environmental sites, 6 body sites and a wound, if present, were cultured with pre-moistened swabs. All nasal swabs were submitted for both a quantitative culture and real-time PCR (Roche Lightcycler, Indianapolis, IN). Results 82 patients had a positive MRSA-PCR at study enrollment. There was a negative correlation of moderate strength between the CT value and the number of MRSA colonies in the nares (r= −0.61, p<0.01). Current antibiotic use was associated with lower levels of MRSA nasal colonization (CT value: 30.2 vs. 27.7, p<0.01). Patients who had concomitant environmental contamination had higher median log MRSA nares count (3.9 vs. 2.5, p=0.01) and lower CT values (28.0 vs. 30.2, p<0.01). However, a ROC curve was unable to identify a threshold MRSA nares count that reliably excluded environmental contamination. Conclusions Patients with a higher burden of MRSA in their nares, based on the CT value, were more likely to contaminate their environment with MRSA. However, contamination of the environment cannot be predicted solely by the degree of MRSA nasal colonization.

Outbreaks in Health Care Settings

“…70 The higher the burden of S aureus in their nares, the more likely the person will shed organisms and have higher degrees of environmental contamination. 71…”

Impact of Antibiotic Treatment on the Burden of Nasal Staphylococcus aureus among Hospitalized Patients

“…S ystemic antibiotic treatment plays a major role in promotion of colonization by health care-associated pathogens and in determining the burden of carriage (1). Antibiotic-induced overgrowth of pathogens may increase the risk for transmission (2)(3)(4)(5). For example, an increased nasal burden of methicillin-resistant Staphylococcus aureus (MRSA) has been associated with environmental contamination (3)(4)(5) and contamination of intact skin (5).…”

“…Antibiotic-induced overgrowth of pathogens may increase the risk for transmission (2)(3)(4)(5). For example, an increased nasal burden of methicillin-resistant Staphylococcus aureus (MRSA) has been associated with environmental contamination (3)(4)(5) and contamination of intact skin (5). In contrast, antibiotics with inhibitory activity against pathogens may suppress colonization if sufficient concentrations are achieved at the site of colonization (1,6).…”

“…Our findings have important clinical implications. Antibiotic-induced overgrowth of S. aureus isolates may increase the risk for transmission by increasing environmental or skin contamination (3)(4)(5). Increased burden of carriage on skin may also increase the risk for infection by facilitating S. aureus contamination of wounds or devices.…”

Shedding of methicillin-resistant Staphylococcus aureus by colonized patients during procedures and patient care activities

“…In previous studies, skin and/ or environmental contamination has been associated with increased nasal density of MRSA, indwelling devices, decreased mobility, and diarrhea in the setting of a high burden of MRSA in stool. [4][5][6][7][8][9] Recently, Pineles et al 10 identified certain types of care activities that were associated with increased risk for contamination of cover gowns and gloves, including wound care, dressing, and providing hygiene and bathing assistance. We hypothesized that medical procedures and patient care activities would similarly facilitate environmental dissemination of MRSA.…”