By Richard R. Watkins, MD, MS, FACP, FIDSA, FISAC

Professor of Internal Medicine, Northeast Ohio Medical University, Rootstown, OH

SYNOPSIS: An observational cohort study found shedding of methicillin-resistant Staphylococcus aureus by colonized patients outside hospital rooms or during outpatient clinic visits occurred more often than in those colonized by multidrug-resistant gram-negative bacilli.

SOURCE: Alhmidi H, Cadnum JL, Koganti S, et al. Shedding of methicillin-resistant Staphylococcus aureus and multidrug-resistant gram-negative bacilli during outpatient appointments and procedures outside hospital rooms. Am J Infect Control 2021;49:991-994.

Patients colonized with pathogenic bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA) or multidrug-resistant gram-negative bacilli (MDR-GNB), are known to shed these organisms in their hospital rooms and during procedures. This leads to contamination of other people, environmental surfaces, and medical equipment. However, less is known about bacterial shedding outside of patient rooms, such as at outpatient clinics, during physical therapy appointments, and in the radiology department. Therefore, Alhmidi and colleagues examined environmental shedding of MRSA and MDR-GNB by colonized patients in settings outside of hospital rooms.

The study was an observational cohort study that included patients in contact precautions for MDR-GNB or MRSA. MDR-GNB were defined as an extended-spectrum beta-lactamase (ESBL)-producing gram-negative bacilli or a carbapenem-resistant gram-negative bacilli. A control group of 10 patients with no history of MRSA or MDR-GNB colonization and with negative baseline cultures also was included. Culture swabs were obtained of the anterior nares to determine MRSA colonization and from the skin and perirectal area for patients with MDR-GNB. Environmental shedding was assessed outside patient rooms for inpatients and during outpatient clinic visits within three months of hospital discharge. The investigators cleaned and disinfected environmental surfaces. Then immediately after appointments, they used culture plates to recover MRSA or MDR-GNB from a standardized group of high-touch surfaces. For the first 10 appointments, they collected cultures before patients entered the room to ensure that no MRSA or MDR-GNB were recoverable.

For patients known to be colonized with MRSA, spa typing was performed on environmental isolates. These were considered to be concordant with nares isolates if the spa type was the same. In those with MDR-GNB colonization, environmental isolates were considered concordant if the perirectal or skin isolates had the same species identification and susceptibility pattern.

There were 39 patients with MRSA colonization and 11 with MDR-GNB included in the study. The frequency of environmental shedding was significantly greater for MRSA (15/39, 38%) compared to MDR-GNB (0/11, 0%; P = 0.02). No MRSA or MDR-GNB were recovered from the 10 control patients. Following two outpatient appointments with MRSA-colonized patients, contamination was detected in the provider work area after a provider’s hands contacted a patient without wearing gloves and did not perform hand hygiene. Spa typing was done on 10 MRSA carriers, of whom eight had the same nasal and environmental isolates identified. Finally, the presence of a wound that was culture-positive for MRSA was the only significant characteristic associated with shedding.


The study by Alhmidi and colleagues demonstrates the high frequency of MRSA shedding into the environment by colonized patients, particularly those with MRSA in their wounds. This provides strong evidence of the need for effective environmental decontamination in outpatient clinics and other sites where inpatient appointments occur, such as physical therapy, to reduce MRSA transmission. It also supports implementing other methods that might lead to less MRSA shedding, such as chlorhexidine bathing, patient hand hygiene, and the use of intranasal mupirocin.

Of equal importance was the finding that MDR-GNB colonization did not lead to similar environmental shedding. This calls into question the appropriateness of contact isolation for patients colonized with MDR-GNB. Contact precautions have a number of potential downsides, including patient dissatisfaction due to less interaction with hospital staff, increased hospital costs (e.g., isolation gowns and gloves), and restricted visitation. These need to be weighed against the potential of transmission of pathogenic bacteria to vulnerable patients, hospital staff members, and objects in the environment, such as medical equipment. Although the results of the study are reassuring in terms of the low risk of MDR-GNB shedding, further research is necessary to replicate this finding.

There are a few limitations to the study. First, the study was conducted at a single Veterans Affairs (VA) hospital, so the population was almost entirely older males. Thus, the results might not be generalizable to other patient groups. Second, there was a relatively small number (n = 11) of patients colonized with MDR-GNB. Third, 20% of the MRSA isolates had spa types different from concurrent nasal isolates, which raises the possibility that some MRSA isolates originated from healthcare workers or another source. Finally, healthcare workers were aware they were being observed by the investigators.

Shedding of MRSA by colonized patients can occur in other areas besides their inpatient rooms. This has important policy ramifications for infection control personnel in their efforts to reduce the transmission of MRSA in healthcare facilities. Fortunately, the risk of transmission of MDR-GNB by colonized patients shedding into the environment appears to be much lower.