MRSA acquisition in hospitals tied to ward characteristics

In hospitals, the risk of acquiring methicillin-resistant Staphylococcus aureus (MRSA) is high in wards that receive a high number of MRSA-colonized patients coming from other wards, according to a Singapore study.

On the other hand, MRSA prevalence among directly admitted patients does not directly contribute to the risk of MRSA acquisition.

“This suggests that, on average, MRSA prevalence among patients transferred from other wards had a stronger effect on MRSA acquisition rate, compared to the prevalence among patients directly admitted to the ward. This effect is further increased in wards that received greater volume of patients,” the investigators noted.

They pointed out that disparities in infection control practices and organizational factors by ward can mean “that intrahospital ward transfer likely changes MRSA acquisition risk experienced by a patient.”

To assess factors associated with MRSA, the investigators used high-resolution electronic medical records of in-patient ward transfers from a large public acute care hospital in Singapore, together with active MRSA admission screening data. The analysis involved a total of 65,428 hospitalization episodes recorded over a period of 4 years in 36 wards. Of these wards, eight (22 percent) were critical care and eight (22 percent) had MRSA-cohorting beds.

Average MRSA prevalence was markedly higher among patients transferred from other wards vs directly admitted patients (10 percent vs 6.8 percent). Overall average hand hygiene compliance was 70 percent, jumping from 64 percent in 2010 to 73 percent in 2013. [PLoS One 2021;16:e025485]

Several ward factors were associated with an increased rate of MRSA acquisition. These included MRSA prevalence among patients transferred from other wards (for every 5-percentage point increase: rate ratio [RR], 7.74, 95 percent confidence interval [CI], 3.88–15.44), critical care ward (RR, 1.72, 95 percent CI, 1.09–2.70), and presence of MRSA cohorting beds (RR, 1.39, 95 percent CI, 1.03–1.90).

Meanwhile, acquisition rates appeared to be lower in oncology wards (vs medical wards: RR, 0.66, 95 percent CI, 0.46–0.94) and among patients who required longer hospitalization (for every 1.5 additional days: RR, 0.70, 95 percent CI, 0.55–0.90).

Patients with conditions that required a longer hospital stay tended to be from oncology wards, intensive care units, and high-dependency units—wards that were likely to have more stringent infection control measures, the investigators said. “Therefore, MRSA acquisition rates were lower in these wards. Unfortunately, data on infection control measures were unavailable, except hand hygiene compliance data.”

However, hand hygiene compliance exerted modest effects on MRSA acquisition in the present study, even though hand hygiene among healthcare workers (HCWs) is considered the primary infection control measure in hospital settings, they added. “This could be due to the coarse temporal resolution of quarterly data that may not accurately capture hand hygiene compliance in the wards. In addition, Hawthorne effect may play a role: HCWs may alter their behaviour during the audit, overestimating hand hygiene compliance.” 

Acute care public hospitals in Singapore previously implemented a multipronged MRSA control strategy that led to a substantial reduction in hospital-acquired MRSA bacteraemia. Despite these efforts, MRSA remains endemic in healthcare settings. A point prevalence survey conducted locally in 2014 indicated that 11.8 percent of patients in a large tertiary public hospital were colonized by MRSA. The prevalence was higher in intermediate (29.9 percent) and long-term (20.4 percent) care facilities. [J Hosp Infect 2013;85:141-148; BMC Infect Dis 2015;15:391; Clin Infect Dis 2017;64:S76-S81]

As such, the investigators called for a more targeted approach to improve the current MRSA control strategy. “In particular, surveillance and control measures should be strengthened in wards with high proportion of MRSA-colonised patients among those transferred from other wards, especially in wards receiving greater volume of transfer patients.”