Household MRSA contamination associated with recurrent infection

1. In this prospective cohort study, household environmental contamination with MRSA was associated with recurrent infection after the initial, index infection.

2. While this study portrayed the household to be a reservoir for clinically relevant infection transmission, the study population was small and the absolute increase in risk for infection among those with home-isolates compared to those without was small.

Evidence Rating Level: 2 (Good)

Study Rundown: Methicillin-resistant Staphylococcus aureus (MRSA) can be a challenging infection to treat. While most infections involve the skin and soft tissues, hematogenous spread can be life threatening. The household has been identified as a primary reservoir and risk factor for recurrent MRSA infection, and there is an increasing interest in developing potential interventional strategies aimed for the home. This study aimed to determine whether household environmental contamination increased the risk for recurrent infection among individuals with community-associated MRSA infection (CA-MRSA).

In the 82 households with an eligible, participating index MRSA case, 35 patients had a recurrent MRSA infection. Thirteen were from the 20 households with MRSA contaminated surfaces, whereas the remaining 22 recurrent infections occurred in households without MRSA contaminated surfaces. This translated to a doubled risk for recurrent infection if there was household environmental contamination. Limitations included their broad exclusion criteria, often not representative of the typical internal medicine ward patients (median age of 30 years for participants, single geographic location, limited diversity). There was also a small sample size representing only 30% of eligible participants.

Click to read the study, published in JAMA Internal Medicine

Relevant Reading: Household transmission of methicillin-resistant Staphylococcus aureus and other staphylococci

In-Depth [prospective cohort]: This study was conducted in New York, USA from November 2011 to June 2014 using patients within the Columbia University Medical Centre catchment area. Patients who had a skin, soft-tissue, blood or urine infections caused by MRSA were identified and study criteria were applied. Patients who lived in long-term care, were hospitalized in the last 6 months, homeless, or those with a chronic illness (i.e., end-stage renal disease) were excluded. Those that agreed to participate were followed for 6-months with an initial home visit and subsequent structured questionnaires. The exposure of interest was concordant environmental contamination (isolate of concordant strain of S. Aureus present on 1 or more environmental surfaces in the home). The outcome of interest was index recurrent infection defined as any self-reported infection among index patients during follow-up. Participants and researchers were blinded to exposure status. Bivariate analysis, χ² and 2-tailed t tests were used for statistical analysis.

Of the 554 culture-positive cases, 262 met inclusion criteria. These eligible participants were contacted and ultimately 83 (31.7%) agreed to participate in this study however one patient did not complete follow-up. The mean age was 30 years old (SD 20, range 1-79). Of the 82 households with an index MRSA case, 20 households (24.4%) had a clinical isolate of the same MRSA strain found on an environmental surface. In total, 35 patients (42.7%) reported a recurrent MRSA infection during follow-up: 13 were from the 20 households with MRSA environmental isolates, and 22 were from the 62 households with no MRSA environmental isolates (p = 0.04). This represented an incident rate ratio of 2.05 (95%CI 1.03-4.10; p = 0.04).

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