Association Between Contact Precautions and Transmission of Methicillin-Resistant Staphylococcus aureus in Veterans Affairs Hospitals

Abstract

Importance: The effectiveness and importance of contact precautions for endemic pathogens has long been debated, and their use has broad implications for infection control of other pathogens.

Objective: To estimate the association between contact precautions and transmission of methicillin-resistant Staphylococcus aureus (MRSA) across US Department of Veterans Affairs (VA) hospitals.

Design, setting, and participants: This retrospective cohort study used mathematical models applied to data from a population-based sample of adults hospitalized in 108 VA acute care hospitals for at least 24 hours from January 1, 2008, to December 31, 2017. Data were analyzed from May 2, 2019, to December 11, 2020.

Exposures: A positive MRSA test result, presumed to indicate contact precautions use according to the VA MRSA Prevention Initiative.

Main outcomes and measures: The main outcome was the association between contact precautions and MRSA transmission, defined as the relative transmissibility attributed to contact precautions. A contact precaution effect estimate (<1 indicates a reduction in transmission associated with contact precautions) was estimated for each hospital and then pooled over time and across hospitals using meta-regression.

Results: In this cohort study of 108 VA hospitals, more than 2 million unique individuals had over 5.6 million admissions, of which 14.1% were presumed to have contact precautions with more than 8.4 million MRSA surveillance tests. Pooled estimates found associations between contact precautions and transmission to be stable from 2008 to 2017, with estimated transmission reductions ranging from 43% (95% credible interval [CrI], 38%-48%) to 51% (95% CrI, 46%-55%). Over the entire 10-year study period, contact precautions reduced transmission 47% (95% CrI, 45%-49%), and the intrafacility autocorrelation coefficient estimate was 0.99, suggesting consistent estimates over time within facilities. Larger facilities and those with higher admission screening compliance observed additional reductions in transmission associated with contact precautions (relative rate, 0.84; 95% CI, 0.74-0.96 and 0.74; 95% CI, 0.58-0.96, respectively) compared with smaller facilities and those with lower admission screening compliance. Facilities in the southern US had a smaller transmission reduction attributable to contact precautions (relative rate, 1.14; 95% CI, 1.01-1.28) compared with facilities in other regions in the US.

Conclusions and relevance: In this cohort study of adults in VA hospitals, transmissibility of MRSA was found to be reduced by approximately 50% among patients with contact precautions. These results provide an explanation for decreasing acquisition rates in VA hospitals since the MRSA Prevention Initiative.

Figure 1.. Transmission Model

Illustration of the underlying transmission model, showing the possible transitions for patient colonization, and the relationship between the unobserved and observed data in the model in 3 scenarios. In (A), the patient remains uncolonized throughout the hospitalization but is assumed to have contact precautions due to a prior positive methicillin-resistant Staphylococcus aureus (MRSA) test result. Both (B) and (C) highlight the potential change in colonization status, with (B) illustrating that colonization does not always coincide with contact precautions and (C) illustrating the allowance for imperfect testing with a false-negative test result.

Figure 2.. Facility-Specific Estimates From 2012 to 2013

Forest plot showing the facility-specific estimates represented by squares, along with the corresponding 95% CIs for each of the facilities during the 2 years from 2012 to 2013. The pooled estimate is represented by the diamond at the bottom, with the width of the diamond indicating the 95% CI for the pooled estimate. The size of the squares reflects the precision of the facility-specific estimates. CP indicates contact precautions.

Figure 3.. Association Between Prevalence and Force of Infection

Illustration of the association between ward prevalence and the estimated force of infection in a single general acute medicine ward contrasting the differential in the transmissibility of patients not with contact precautions (blue) with those with contact precautions (orange). The dashed lines represent the 95% CIs.

Figure 4.. Association Between Facility Measures and Estimated Effectiveness of Contact Precautions

Bubble plot showing the association between the transmission rate estimates and the contact precautions (CP) effect estimate (A). The lines show the association between the estimated CP effect parameter and the transmission rate (solid line) and the 95% CIs (dashed lines), and the dotted line represents no effect. The blue circles are the estimates for each facility with the size of the dots reflecting the precision. Larger dots reflect low variance in the estimates. There is a slight increasing association between transmission rate and CP effect. On the right (B) is a bubble plot showing the association between contact precautions effect and proportion of admissions having an admission test. A decreasing association between the proportion of admission tests and the contact precautions effect parameter is shown.