Carriers of methicillin-resistant Staphylococcus aureus (MRSA) serve as reservoirs and vectors for cross-transmission.Reference Merrer, Santoli, Appere de Vecchi, Tran, De Jonghe and Outin ¹ Nevertheless, topical decolonization to eradicate MRSA carriage is used infrequently in settings with endemic MRSA because of logistical challenges, low chances of success, and the risk of resistance.Reference Lee, Macedo-Vinas and Francois ² Few studies have described determinants of successful MRSA decolonization among patients receiving topical decolonization therapy.Reference Harbarth, Liassine, Dharan, Herrault, Auckenthaler and Pittet ^{3 –} Reference Kohler, Bregenzer-Witteck, Rettenmund, Otterbech and Schlegel ⁷

We recently reported the results of a double-blind, placebo-controlled randomized trial that demonstrated the failure of polyhexanide to eliminate MRSA carriage.Reference Landelle, von Dach and Haustein ⁸ On average, the decolonization efficacy was 31.5% for the entire population, with a marginally higher success rate (33.8%) in the polyhexanide group. Using data from this randomized controlled trial (RCT), we assessed possible determinants of successful MRSA decolonization.

A full description of the RCT has been reported elsewhere.Reference Landelle, von Dach and Haustein ⁸ In brief, we tested the efficacy of polyhexanide versus placebo solution, applied for 10 days in the nose and on the skin of MRSA carriers. Control swabs were taken from nares and the inguinal/perineal region, according to our local practices and other evidence.Reference Harbarth, Schrenzel, Akakpo, Renzi and Ricou ⁹ Patients with positive tracheal or chronic wound swabs were excluded from the RCT. Data were recorded prospectively with patients’ consent.Reference Landelle, von Dach and Haustein ⁸ Using data from this RCT, we conducted a retrospective, unmatched case-control study to assess determinants associated with successful MRSA decolonization among participants. Cases were defined as patients with a negative MRSA screening result at the end of the study. The control group consisted of patients who were still MRSA-positive at end of the follow-up period. We included in the case-control study all patients from the RCT with a MRSA-positive swab at inclusion and follow-up screening at day 28. Possible determinants of successful MRSA decolonization included various patient and treatment characteristics. Dependence of patients was defined as a partial or total inability of a person to perform the activities of daily life without help.

We used the Student t test and the two-sample Wilcoxon rank-sum test for continuous variables, and Pearson’s χ² test and Fisher’s exact test for categorical variables when appropriate. All variables associated with an increased likelihood of MRSA decolonization with a value of P≤.25 in the univariate analysis were included in a multivariate logistic regression model using a forward stepwise procedure. Log linearity was checked for continuous variables and, if not fulfilled, the variables were converted into categorical variables. The validity of the resulting model was verified using the Hosmer-Lemeshow test. Analyses were performed using Stata 12 software.

Among the 150 patients included in the RCT, 135 met the inclusion criteria for the case-control study. There were 46 MRSA-negative cases (34.1%) and 89 MRSA-positive controls (65.9%) at end of follow-up. Table 1 describes important patient and treatment features. According to our univariate analysis, cases were more likely to live without assistance, having only the nose or groin colonized (and not both), and a shorter length of hospital stay after treatment was initiated. The MRSA-negative patients also tended to be younger, to be without invasive equipment, and without a malignancy or obstructive pulmonary disease. No association was found between MRSA decolonization success and the following variables: gender, body-mass index, other comorbidities, McCabe score, skin damage, antibiotic treatment, MRSA strain type, MRSA quantity at baseline, newly identified MRSA status, polyhexanide treatment, and location of treatment administration.

TABLE 1 Patients and Treatment Characteristics, Univariate and Multivariate Logistic Regression to Predict Successful MRSA Decolonization

NOTE. BMI, body mass index; COPD, chronic obstructive pulmonary disease; MLST, multilocus sequence typing; MRSA, methicillin-resistant Staphylococcus aureus; OR, odds ratio; aOR, adjusted odds ratio; SD, standard deviation; ULR, univariate logistic regression.

^a Invasive devices: central venous catheter, peripheral venous catheter, implantable venous access device, or urinary catheter.

^b Anti-MRSA therapy: vancomycin, linezolid, trimethoprim-sulfamethoxazole, or rifampicin.

^c Endemic MRSA clone at the study site (mupirocin- and chlorhexidine-resistant).

^d Other non-endemic clones (mupirocin-susceptible).

According to our multivariate analysis (Table 1), 2 independent factors were associated with successful MRSA decolonization: independent status (adjusted odds ratio [aOR], 2.83; 95% CI, 1.26–6.34; P=.011) and only 1 MRSA-colonized body site at baseline (aOR, 2.16; 95% CI, 1.03–4.56; P=.042). The Hosmer-Lemeshow test indicated adequate model fit (χ²=0.58; P=.748).

This case-control study based on a clinical trial population highlights 2 determinants of successful MRSA decolonization: independent status of patients and single-body-site MRSA carriage at baseline (ie, nose or groin). The results are consistent with previous studies in which a higher number of colonized sites were associated with decolonization failure.Reference Harbarth, Liassine, Dharan, Herrault, Auckenthaler and Pittet ³ Concerning the status of independence in daily activities, it has not been associated with a higher likelihood of MRSA decolonization thus far. Only the dependent status of a patient was associated with poor compliance to MRSA decolonization treatment and consequently decolonization failure.Reference Ammerlaan, Kluytmans and Berkhout ⁴ Other risk factors have been associated with lower chances of MRSA decolonization in previous studies such as an older age; recent antibiotic use (particularly fluoroquinolones); immunosuppressive treatment; and presence of a central venous catheter, skin wound, or pulmonary diseases.Reference Lee, Macedo-Vinas and Francois ^{2 ,} Reference Ammerlaan, Kluytmans and Berkhout ^{4 –} Reference Marschall and Muhlemann ⁶ Although these variables have been included in this analysis, their absence was not associated with successful MRSA decolonization; this might be explained by the low frequency of certain exposures.

A limitation of this study was the reduced number of eligible patients for the RCT, excluding the sickest patients and those receiving systemic antibiotic treatment for MRSA infection. Thus, this study population may not be representative of all MRSA patients. However, the prospective design and data collection remains a strength of this study. Furthermore, a few determinants known to be associated with MRSA decolonization failure could not be evaluated, including colonization at other body sites (eg, throat, axilla) and carriage among household contacts.Reference Lee, Macedo-Vinas and Francois ^{2 ,} Reference Ammerlaan, Kluytmans and Berkhout ^{4 ,} Reference Bocher, Skov and Knudsen ^{5 ,} Reference Kohler, Bregenzer-Witteck, Rettenmund, Otterbech and Schlegel ^{7 ,} Reference Buehlmann, Frei, Fenner, Dangel, Fluckiger and Widmer ¹⁰

Based on these data, we can now better target potential patients for topical MRSA decolonization therapy. By choosing independent patients with only 1 MRSA colonization site, we may increase the effectiveness of decolonization treatment and limit the emergence of resistance to topical decolonization agents.Reference Lee, Macedo-Vinas and Francois ²