Fran Lowry

May 19, 2015

ORLANDO, Florida — Almost 20% of patients with methicillin-resistant Staphylococcus aureus (MRSA) skin and soft tissue infection (SSTI) will remain persistently colonized, according to new research.

Colonization of people in a patient's household could be one reason for this persistence, suggesting a possible role for total household decolonization, said Valerie Cluzet, PhD, from the University of Pennsylvania in Philadelphia.

In fact, "MRSA colonization in the community is a major problem," Dr Cluzet told Medscape Medical News.

"We know it's the most common cause of purulence in the community, causing abscesses and boils, and we know that colonization is a risk factor for skin and soft tissue infection," she explained. "We wanted to take a systematic approach to studying colonization in patients who had MRSA infections and determine the effect of having household members who may or may not be colonized."

Dr Cluzet presented results from the prospective cohort study here at the Society for Healthcare Epidemiology of America Spring 2015 Conference.

She and her colleagues evaluated 243 patients who presented to an emergency room or primary care doctor with an MRSA infection at one of five adult and pediatric academic medical centers from January 2010 to December 2012.

Dr Valerie Cluzet

The patients and their household members took nose, groin, and armpit swab samples every 2 weeks for 6 months and mailed them to Dr Cluzet's laboratory for analysis of MRSA colonization.

Clearance of colonization was defined as two consecutive sampling periods with negative cultures. Study participants who did not meet the clearance criteria by the end of the study period were deemed to be persistently colonized.

Of the 243 index patients, 48 (19.8%) remained persistently colonized.

Patients with persistent colonization tended to be older than patients who achieved clearance, more likely to have been prescribed mupirocin within 14 days of the MRSA diagnosis, more likely to have a household member with MRSA colonization, and less likely to have been prescribed clindamycin.

Table. Factors Related to Persistent Colonization

Factor Odds Ratio 95% Confidence Interval P Value
Each additional 10 years of age 1.90 1.03–1.37 .02
Mupirocin prescription 2.38 1.08–5.27 .032
Each household member colonized 1.15 1.02–1.29 .018
Clindamycin prescription 0.32 0.15–0.70 .004

 

"These results give us an idea of who is going to be persistently colonized with MRSA, and will help us better target that population," said Dr Cluzet. "We may have to advise not only the patients but also the people they are living with to use bleach baths and mupirocin to get rid of the colonization."

The fact that mupirocin is associated with a higher risk for persistent colonization does not mean that the drug is a causative factor, she pointed out.

"I think being prescribed mupirocin is more a marker of higher-risk individuals, who probably got the drug because they might have had infections in the past or were in some higher-risk group," she explained.

The fact that clindamycin was associated with fewer cases of persistent colonization, however, does merit further study.

"No one has found an association with antibiotics in terms of breaking up colonization," Dr Cluzet reported. "I think we could argue for studying clindamycin more to see whether using it specifically for the treatment of MRSA infection might decrease the burden of colonization, and maybe ultimately the burden of recurring infection."

Household Members Need Decolonization, Too

Dr Silvia Munoz-Price

"This is an interesting retrospective cohort that shows that persistent MRSA colonization is associated with a couple of variables, the most interesting being the presence of a family member concomitantly colonized with MRSA," said Silvia Munoz-Price, MD, from Froedtert & the Medical College of Wisconsin in Milwaukee.

"This not only makes biological plausibility, but is also concordant with epidemiologic studies that show that the higher the number of nearby patients positive for a resistant organism such as MRSA, the higher the likelihood of horizontal transmission," she told Medscape Medical News.

On the basis of these results, "we should consider decolonization interventions, such as chlorhexidine skin disinfection, not only for the known MRSA patient, but also for household contacts," said Dr Munoz-Price.

"The association between clindamycin and the lower risk of persistent colonization is interesting, but might be confounded. This needs to be further explored in other studies," she added.

Dr Cluzet and Dr Munoz-Price have disclosed no relevant financial relationships.

Society for Healthcare Epidemiology of America (SHEA) Spring 2015 Conference: Abstract 7130. Presented May 16, 2015.

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