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Household MRSA contamination predicted human recolonization



– Patients who were successfully treated for methicillin-resistant Staphylococcus aureus infections were about four times more likely to become recolonized if their homes contained MRSA, according to the results of a longitudinal household study.

“Many of these homes were contaminated with a classic community strain,” Meghan Frost Davis, DVM, PhD, MPH, said during an oral presentation at an annual meeting on infectious disease. “We need to think about interventions in the home environment to improve our ability to achieve successful decolonization.”

Meghan Davis, DVM, PhD, MPH of Johns Hopkins Bloomberg School of Public Health in Baltimore. Amy Karon/Frontline Medical News

Dr. Meghan Davis

However, the best way to rid a home of MRSA remains unclear, said Dr. Davis of Johns Hopkins Bloomberg School of Public Health in Baltimore. “We looked very closely at environmental contamination and found that cleaning the home the same day or within 3 days did not significantly decrease our recovery of MRSA,” she said. “I can’t tell you that scrubbing your house from top to bottom doesn’t work, but I also don’t have evidence yet that it does.”

Importantly, Dr. Davis and her associates recently published another study in which biocidal disinfectants failed to eliminate MRSA from homes and appeared to increase the risk of multi-drug resistance (Appl Environ Microbiol. online 22 September 2017, doi: 10.1128/AEM.01369-17). Her team is testing MRSA isolates for resistance to disinfectants and hopes to have more information in about a year, she said. Until then, Dr. Davis suggests advising patients with MRSA to clean sheets and pillowcases frequently.

S. aureus can survive in the environment for long periods. In one case, a MRSA strain tied to an outbreak was cultured from a dry mop that had been locked in a closet for 79 months, Dr. Davis said. “This is concerning because the home is a place that receives bacteria from us,” she said. “A person who was originally colonized or infected with MRSA may clear naturally or through treatment, but the environment may become a reservoir for recolonization and infection.”

To better understand the role of this reservoir, she and her associates recruited 88 index outpatients with MRSA skin and soft tissue infections who were part of a randomized trial of MRSA decolonization strategies. At baseline and 3 months later, the researchers sampled multiple sites in each patient’s home and all household pets. Patients and household members also swabbed themselves in multiple body sites every 2 weeks for up to 3 months. Swabs were cultured in enrichment broth, and positive results were confirmed by PCR (Infect Control Hosp Epidemiol. 2016 Oct;37[10]:1226-33. doi: 10.1017/ice.2016.138. Epub 2016 Jul 28).

Even after accounting for potential confounders, household contamination with MRSA was associated with about a three- to five-fold increase in the odds of human colonization, which was statistically significant. Seventy percent of households had at least one pet, but only 10% had a pet colonized with MRSA. Having such a pet increased the risk of human carriage slightly, but not significantly. However, having more than one pet did predict human colonization, Dr. Davis said. Even if pets aren’t colonized, they still can carry MRSA on “the petting zone” – the top of the head and back, she explained. Thus, pets can serve as reservoirs for MRSA without being colonized.

In all, 53 index patients had at least two consecutive negative cultures and thus were considered decolonized. However, 43% of these individuals were subsequently re-colonized, and those whose homes contained MRSA at baseline were about 4.3 times more likely to become recolonized than those whose households cultured negative (hazard ratio, 4.3; 95% CI, 1.2-16; P less than .03).

A total of six patients were persistently colonized with MRSA, and 62% of contaminated homes tested positive for MRSA Staph protein A (spa) type t008, a common community-onset strain. Living in one of these households significantly increased the chances of persistent colonization (odds ratio, 12.7; 95% CI, 1.33-122; P less than .03).

Pets testing positive for MRSA always came from homes that also tested positive, so these factors couldn’t be disentangled, Dr. Davis said. Repository surfaces in homes – such as the top of a refrigerator – were just as likely to be contaminated with MRSA as high-touch surfaces. However, pillowcases often were most contaminated of all. “If I can give you one take-home message, when you treat people with MRSA, you may want to tell them to clean their sheets and pillowcases a lot.”

Dr. Davis and her associates had no disclosures.

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