Low-Level Mupirocin, Chlorhexidine Resistance Thwart MRSA Control in Hospitals

BOSTON – Efforts to control hospital-acquired methicillin-resistant Staphylococcus aureus infections could be sabotaged by infectious isolates with low-level resistance to the topical anti-infectives mupirocin and chlorhexidine, according to the findings of retrospective case-control study.

Emergence of resistance and its impact should be monitored in institutions with widespread use of these agents. “Alternative agents may be required to effectively control MRSA in setting with high prevalence of resistance,” the study’s lead investigator, Dr. Andie S. Lee, said at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy.

The study involved patients who underwent at least 3 days of decolonization therapy for MRSA with mupirocin and chlorhexidine, and it showed that even low-level mupirocin resistance was associated with a more than threefold increased risk of decolonization therapy failure. Chlorhexidine resistance was associated with a 10-fold increased risk, said Dr. Lee of the University of Geneva Hospitals.

Other significant risk factors identified in a multivariate analysis included prior hospitalization, age, presence of wounds or pressure sores, recent antibiotic use, and use of a central venous catheter.

She and her colleagues compared factors that might have contributed to decolonization failure among 75 MRSA carriers, compared with 75 successfully decolonized controls, matched by year of decolonization therapy.

Failed decolonization was defined as one or more positive MRSA cultures 1-12 months after decolonization. Successful decolonization was defined by six or more consecutive negative MRSA swabs with the most-recent sample within 2 years of decolonization therapy. Alternatively, if the last follow-up sample was more than 2 years after decolonization therapy, all MRSA swabs must have been negative, Dr. Lee explained at the meeting, which was sponsored by the American Society for Microbiology.

Out of a sample population of 911 patients, only 87 were successfully decolonized, and 12 of these patients were excluded by study criteria (6 for contaminated or nonviable MRSA samples and 6 for high-level mupirocin resistance of isolates) leaving 75 controls paired with 75 cases. The groups were well matched by baseline characteristics, except that more successfully decolonized patients (controls) were slightly younger (mean age 68 vs. 76 years), and had significantly shorter stays (mean 27 vs. 49 days).

The investigators found that cases were significantly more likely than were controls to have low-level resistance to mupirocin (64% vs. 35%, odds ratio 3.4), to carry the V588F mupirocin-resistance mutation (69% vs. 36%, OR 4.6), and to have low-level resistance associated with the mupA gene (24% vs. 8%, OR 5.1).

Cases also were significantly more likely than were controls to be carriers of the qacA/B efflux gene (91% vs. 68%).

In multivariate logistic regression analyses that controlled for demographic factors, comorbidities, and health care exposures, independent risk factors associated with persistent colonization with MRSA were age (OR 1.04 for every year), prior hospitalization in the past 2 years (OR 2.4), wounds/pressure sores (OR 5.7), exposure to antibiotics inactive against MRSA (OR 3.1), and use of a central venous catheter (OR 5.7).

Disclosures: The study was internally funded. Neither Dr. Lee nor her coinvestigators reported having any conflicts of interest.

BOSTON – Efforts to control hospital-acquired methicillin-resistant Staphylococcus aureus infections could be sabotaged by infectious isolates with low-level resistance to the topical anti-infectives mupirocin and chlorhexidine, according to the findings of retrospective case-control study.

Emergence of resistance and its impact should be monitored in institutions with widespread use of these agents. “Alternative agents may be required to effectively control MRSA in setting with high prevalence of resistance,” the study’s lead investigator, Dr. Andie S. Lee, said at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy.

The study involved patients who underwent at least 3 days of decolonization therapy for MRSA with mupirocin and chlorhexidine, and it showed that even low-level mupirocin resistance was associated with a more than threefold increased risk of decolonization therapy failure. Chlorhexidine resistance was associated with a 10-fold increased risk, said Dr. Lee of the University of Geneva Hospitals.

Other significant risk factors identified in a multivariate analysis included prior hospitalization, age, presence of wounds or pressure sores, recent antibiotic use, and use of a central venous catheter.

She and her colleagues compared factors that might have contributed to decolonization failure among 75 MRSA carriers, compared with 75 successfully decolonized controls, matched by year of decolonization therapy.

Failed decolonization was defined as one or more positive MRSA cultures 1-12 months after decolonization. Successful decolonization was defined by six or more consecutive negative MRSA swabs with the most-recent sample within 2 years of decolonization therapy. Alternatively, if the last follow-up sample was more than 2 years after decolonization therapy, all MRSA swabs must have been negative, Dr. Lee explained at the meeting, which was sponsored by the American Society for Microbiology.

Out of a sample population of 911 patients, only 87 were successfully decolonized, and 12 of these patients were excluded by study criteria (6 for contaminated or nonviable MRSA samples and 6 for high-level mupirocin resistance of isolates) leaving 75 controls paired with 75 cases. The groups were well matched by baseline characteristics, except that more successfully decolonized patients (controls) were slightly younger (mean age 68 vs. 76 years), and had significantly shorter stays (mean 27 vs. 49 days).

The investigators found that cases were significantly more likely than were controls to have low-level resistance to mupirocin (64% vs. 35%, odds ratio 3.4), to carry the V588F mupirocin-resistance mutation (69% vs. 36%, OR 4.6), and to have low-level resistance associated with the mupA gene (24% vs. 8%, OR 5.1).

Cases also were significantly more likely than were controls to be carriers of the qacA/B efflux gene (91% vs. 68%).

In multivariate logistic regression analyses that controlled for demographic factors, comorbidities, and health care exposures, independent risk factors associated with persistent colonization with MRSA were age (OR 1.04 for every year), prior hospitalization in the past 2 years (OR 2.4), wounds/pressure sores (OR 5.7), exposure to antibiotics inactive against MRSA (OR 3.1), and use of a central venous catheter (OR 5.7).

Disclosures: The study was internally funded. Neither Dr. Lee nor her coinvestigators reported having any conflicts of interest.

BOSTON – Efforts to control hospital-acquired methicillin-resistant Staphylococcus aureus infections could be sabotaged by infectious isolates with low-level resistance to the topical anti-infectives mupirocin and chlorhexidine, according to the findings of retrospective case-control study.

Emergence of resistance and its impact should be monitored in institutions with widespread use of these agents. “Alternative agents may be required to effectively control MRSA in setting with high prevalence of resistance,” the study’s lead investigator, Dr. Andie S. Lee, said at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy.

The study involved patients who underwent at least 3 days of decolonization therapy for MRSA with mupirocin and chlorhexidine, and it showed that even low-level mupirocin resistance was associated with a more than threefold increased risk of decolonization therapy failure. Chlorhexidine resistance was associated with a 10-fold increased risk, said Dr. Lee of the University of Geneva Hospitals.

Other significant risk factors identified in a multivariate analysis included prior hospitalization, age, presence of wounds or pressure sores, recent antibiotic use, and use of a central venous catheter.

She and her colleagues compared factors that might have contributed to decolonization failure among 75 MRSA carriers, compared with 75 successfully decolonized controls, matched by year of decolonization therapy.

Failed decolonization was defined as one or more positive MRSA cultures 1-12 months after decolonization. Successful decolonization was defined by six or more consecutive negative MRSA swabs with the most-recent sample within 2 years of decolonization therapy. Alternatively, if the last follow-up sample was more than 2 years after decolonization therapy, all MRSA swabs must have been negative, Dr. Lee explained at the meeting, which was sponsored by the American Society for Microbiology.

Out of a sample population of 911 patients, only 87 were successfully decolonized, and 12 of these patients were excluded by study criteria (6 for contaminated or nonviable MRSA samples and 6 for high-level mupirocin resistance of isolates) leaving 75 controls paired with 75 cases. The groups were well matched by baseline characteristics, except that more successfully decolonized patients (controls) were slightly younger (mean age 68 vs. 76 years), and had significantly shorter stays (mean 27 vs. 49 days).

The investigators found that cases were significantly more likely than were controls to have low-level resistance to mupirocin (64% vs. 35%, odds ratio 3.4), to carry the V588F mupirocin-resistance mutation (69% vs. 36%, OR 4.6), and to have low-level resistance associated with the mupA gene (24% vs. 8%, OR 5.1).

Cases also were significantly more likely than were controls to be carriers of the qacA/B efflux gene (91% vs. 68%).

In multivariate logistic regression analyses that controlled for demographic factors, comorbidities, and health care exposures, independent risk factors associated with persistent colonization with MRSA were age (OR 1.04 for every year), prior hospitalization in the past 2 years (OR 2.4), wounds/pressure sores (OR 5.7), exposure to antibiotics inactive against MRSA (OR 3.1), and use of a central venous catheter (OR 5.7).

Disclosures: The study was internally funded. Neither Dr. Lee nor her coinvestigators reported having any conflicts of interest.