Abstract
Chlorhexidine has been increasingly utilized in outpatient settings to control methicillin-resistant Staphylococcus aureus (MRSA) outbreaks and as a component of programs for MRSA decolonization and prevention of skin and soft-tissue infections (SSTIs). The objective of this study was to determine the prevalence of chlorhexidine resistance in clinical and colonizing MRSA isolates obtained in the context of a community-based cluster-randomized controlled trial for SSTI prevention, during which 10,030 soldiers were issued chlorhexidine for body washing. We obtained epidemiological data on study participants and performed molecular analysis of MRSA isolates, including PCR assays for determinants of chlorhexidine resistance and high-level mupirocin resistance and pulsed-field gel electrophoresis (PFGE). During the study period, May 2010 to January 2012, we identified 720 MRSA isolates, of which 615 (85.4%) were available for molecular analysis, i.e., 341 clinical and 274 colonizing isolates. Overall, only 10 (1.6%) of 615 isolates were chlorhexidine resistant, including three from the chlorhexidine group and seven from nonchlorhexidine groups (P > 0.99). Five (1.5%) of the 341 clinical isolates and five (1.8%) of the 274 colonizing isolates harbored chlorhexidine resistance genes, and four (40%) of the 10 possessed genetic determinants for mupirocin resistance. All chlorhexidine-resistant isolates were USA300. The overall prevalence of chlorhexidine resistance in MRSA isolates obtained from our study participants was low. We found no association between extended chlorhexidine use and the prevalence of chlorhexidine-resistant MRSA isolates; however, continued surveillance is warranted, as this agent continues to be utilized for infection control and prevention efforts.
INTRODUCTION
Skin and soft-tissue infections (SSTIs), particularly those attributed to methicillin-resistant Staphylococcus aureus (MRSA), remain a persistent cause of morbidity in community settings. Over the past decade, ambulatory care and emergency department visits for SSTIs have nearly doubled (1, 2). The emergence of MRSA, especially strain USA300 (3), as a community pathogen is recognized as underlying this surge in SSTI rates (1, 4). Individuals in congregate settings, such as children in day care centers, athletes, inmates, and military personnel, are at increased risk for MRSA SSTIs (5–8).
Chlorhexidine, a topical antiseptic, has had a longstanding role in infection prevention in health care settings (9) and has been increasingly utilized in outpatient settings (9). It has been an integral component of prevention and control measures during MRSA outbreaks (5, 10, 11). Additionally, chlorhexidine has been demonstrated to be effective against recurrent MRSA SSTIs (12) and in limiting the household spread of SSTIs (13) and is recommended when MRSA decolonization of individuals is a goal (14). In the absence of an effective S. aureus vaccine (15), chlorhexidine has also been employed as an SSTI prevention strategy among military trainees, a group known to be at increased risk for MRSA colonization and disease (16, 17).
The increased use of chlorhexidine in SSTI prevention has raised concerns about the possible emergence of chlorhexidine-resistant strains (18, 19). The epidemiology of chlorhexidine-resistant MRSA in health care settings has been described (20, 21); however, there are limited data with regard to its prevalence in community-based settings (22, 23). Moreover, few studies have evaluated the association between concurrent chlorhexidine use and the prevalence of chlorhexidine-resistant S. aureus (24, 25). We recently performed a large-scale, field-based, cluster-randomized trial evaluating the effectiveness of chlorhexidine against MRSA SSTIs among high-risk U.S. Army recruits in basic training at Fort Benning, Georgia (26). The objective of the current study was to determine the prevalence of chlorhexidine resistance in clinical and colonizing MRSA isolates obtained in the context of this cluster-randomized controlled trial.
MATERIALS AND METHODS
Study design and population.
The methods of the cluster-randomized trial have been reported previously; in brief, a 20-month investigation, from May 2010 to January 2012, was conducted to evaluate hygiene-based intervention strategies to reduce SSTI incidence among infantry trainees at Fort Benning, Georgia (26). The trial involved randomization, by training company, to three study groups with various intervention components. Recruits in the standard group received an educational briefing on MRSA SSTI recognition and prevention. Recruits in the enhanced standard group received, in addition to the briefing, supplemental educational material and a first aid kit and were instructed to take a weekly 10-min shower in addition to routine showering. Recruits in the chlorhexidine group received an 8-oz bottle of 4% chlorhexidine (Hibiclens; Mölnlycke Heath Care, Norcross, GA) to use during the weekly 10-min shower.
Trainees who presented to the Troop Medical Clinic (TMC) with an SSTI during training were approached and consented to allow investigators to abstract SSTI-related information from their clinical records and to obtain clinical specimens collected during routine care. Subjects were also asked to complete a questionnaire assessing personal hygiene practices, compliance with the hygiene-based intervention, and knowledge of SSTIs, particularly MRSA SSTIs, and to provide a nasal swab. Some trainees presenting to the TMC for noninfectious conditions, such as musculoskeletal injuries or physical therapy, were also approached for enrollment in the study, as controls. They completed the same questionnaire as subjects with SSTIs and also provided nasal swabs for evaluation. This study was approved by the Infectious Disease Institutional Review Board of the Uniformed Services University (protocol IDCRP-055).
Specimen collection, laboratory methods, and antimicrobial susceptibility testing.
Clinical culture specimens were obtained from purulent SSTIs as part of routine care and were processed at the Martin Army Community Hospital microbiology laboratory, according to standard techniques. Study personnel obtained bilateral anterior nares swabs from trainees at the time of enrollment, using BBL CultureSwabs (BD Diagnostic Systems, Sparks, MD). These specimens were placed in 5 ml of Trypticase soy broth (TSB) supplemented with 6.5% NaCl (BBL; BD Diagnostic Systems, Sparks, MD) and were incubated for 18 to 24 h at 35°C. After incubation, a 75-μl aliquot of broth was plated on mannitol salt agar (MSA). Mannitol-fermenting colonies were isolated, plated on Trypticase soy agar with 5% sheep's blood, and incubated overnight. S. aureus isolates were identified based on colony morphology, Gram staining, latex agglutination (Staphaurex; Remel, Lenexa, KS), and slide catalase testing results. S. aureus isolates were tested with oxacillin screening agar (Mueller-Hinton agar with oxacillin at 6 μg/ml; Becton, Dickinson). Using MicroScan WalkAway-96 (DadeBehring, Inc., Deerfield, IL), all MRSA isolates underwent susceptibility testing with ciprofloxacin, clindamycin, daptomycin, erythromycin, gentamicin, linezolid, rifampin, tetracycline, and trimethoprim-sulfamethoxazole. MIC breakpoints and quality control protocols were used according to standards established by the Clinical and Laboratory Standards Institute (CLSI) (27). Inducible clindamycin resistance was assessed with a double-disk diffusion test (28).
Detection of chlorhexidine resistance and high-level mupirocin resistance.
DNA was extracted using a QIAmp DNA minikit (Qiagen, Valencia, CA), according to the manufacturer's instructions. A previously described real-time quadruplex PCR assay was used in duplicate, to confirm methicillin resistance in S. aureus (mecA and femA) and to detect high-level mupirocin resistance (mupA) and chlorhexidine resistance (qacA/B) simultaneously (23). We defined chlorhexidine resistance on the basis of MRSA isolates possessing qacA/B. There are no CLSI methods for testing susceptibility to chlorhexidine; however, we used standard broth dilution techniques to test all MRSA isolates (29). We used 4% chlorhexidine gluconate (Hibiclens) as the starting material and ATCC 700699 as our control strain (22). Isolates that were positive for mupA underwent MIC determinations by Etest (bioMérieux, St. Louis, MO). We used the following MIC breakpoints for definitions: susceptible, ≤4 μg/ml; low-level resistance, 8 to 64 μg/ml; high-level resistance, ≥512 μg/ml (30).
Pulsed-field gel electrophoresis.
We performed pulsed-field gel electrophoresis (PFGE), using SmaI (Roche Molecular Biochemicals) as a restriction endonuclease, for all available MRSA isolates (31). PFGE findings were resolved and analyzed using BioNumerics (Applied Math, Austin, TX), and isolates were grouped into PFGE types using Dice coefficients and 80% similarity, as described previously (32). We obtained control strains of known PFGE types from the Network on Antimicrobial Resistance in Staphylococcus aureus (NARSA).
Statistical analysis.
Differences in proportions were evaluated by the chi-square test or Fisher's exact test, as appropriate. Median ages were compared using the Kruskal-Wallis H test. Analysis of variance (ANOVA) was used to analyze other continuous variables. All tests of significance were two tailed. P values of ≤0.05 were considered significant. Statistical analyses were performed with SAS version 9.2 (SAS Institute, Cary, NC).
RESULTS
Study population.
A total of 30,209 trainees (all male) constituted the overall study population, and 10,030 (33.2%) were issued chlorhexidine during the study period. Trainees were assigned to chlorhexidine-randomized battalions over the duration of the study period, and the distribution did not vary by study month (data not shown). During the investigation, 1,203 (4.0%) trainees with SSTIs were enrolled in the study. Of the 1,203 SSTIs, 650 (54.0%) had a drainable focus and were cultured; 550 (84.6%) of those were culture positive for S. aureus (57.5% MRSA). Subjects with MRSA SSTIs were young (median age, 19 years [range, 17 to 37 years]) and predominately white (80.5%) (Table 1). Among subjects with SSTIs, no demographic differences were observed between study groups. Control subjects were similar in age to subjects with SSTIs (median age, 20 years [range, 17 to 42 years]).
TABLE 1.
Characteristics of MRSA cases by study group
| Characteristic | Standard (n = 78) | Enhanced standard (n = 121) | Chlorhexidine (n = 84) | P |
|---|---|---|---|---|
| Race/ethnicity, no. (%)a | ||||
| White, non-Hispanic | 21 (80.8) | 40 (74.1) | 30 (90.9) | 0.61 |
| Hispanic | 2 (7.7) | 8 (14.8) | 2 (6.1) | |
| Black, non-Hispanic | 2 (7.7) | 3 (5.6) | 1 (3.0) | |
| Other, non-Hispanic | 1 (3.8) | 3 (5.6) | 0 (0.0) | |
| Age, median (range) | 20 (17–37) | 19 (17–34) | 19 (17–28) | |
| Clinical infection, no. (%) | 0.03 | |||
| More than one | 32 (41.0) | 35 (28.9) | 37 (44.1) | |
| Abscess | 22 (28.2) | 58 (47.9) | 37 (44.1) | |
| Cellulitis | 21 (26.9) | 22 (18.2) | 8 (9.5) | |
| Folliculitis | 3 (3.9) | 2 (1.7) | 1 (1.2) | |
| Infected blister | 0 (0.0) | 3 (2.5) | 1 (1.2) | |
| Impetigo | 0 (0.0) | 1 (0.8) | 0 (0.0) | |
| Site of infection, no. (%) | 0.56 | |||
| Lower extremity | 33 (42.3) | 56 (46.3) | 37 (44.1) | |
| Upper extremity | 20 (25.6) | 38 (31.4) | 21 (25.0) | |
| More than one | 18 (23.1) | 17 (14.1) | 17 (20.2) | |
| Thorax | 4 (5.1) | 5 (4.1) | 1 (1.2) | |
| Head | 2 (2.6) | 3 (2.5) | 4 (4.8) | |
| Groin/inguinal/perineal area | 1 (1.3) | 2 (1.7) | 4 (4.8) | |
| Time from training start to first MRSA clinical isolate (days) | ||||
| Mean ± SD | 66.6 ± 25.1 | 61.7 ± 26.6 | 66.3 ± 25.6 | 0.32 |
| Range | 23–118 | 20–118 | 20–124 |
Race/ethnicity information was available for 26 subjects in the standard group, 54 in the enhanced standard group, and 33 in the chlorhexidine group.
Analysis of clinical MRSA isolates.
The clinical care of the 316 subjects with MRSA SSTIs yielded 382 MRSA isolates. Of these clinical isolates, 341 isolates (89.3%) from 283 subjects were available for molecular analysis, including 93 from the standard group, 143 from the enhanced standard group, and 105 from the chlorhexidine group. No differences in demographic or clinical characteristics were observed when subjects who contributed isolates for molecular analysis were compared with those who did not (data not shown). Furthermore, the proportions of unavailable isolates were evenly distributed across study groups.
Among clinical MRSA isolates, there was no difference in the prevalence of genetic determinants of chlorhexidine resistance between study groups. Of the 341 clinical MRSA isolates tested, only five (1.5%) were positive for qacA/B, including three from the standard group and two from the chlorhexidine group (3.2% and 1.9%, respectively; P = 0.64). In broth dilution testing of these five isolates, two of the isolates, both from the standard group, had a chlorhexidine MIC of 4 μg/ml. The remaining three isolates had a chlorhexidine MIC of 2 μg/ml. All five isolates were USA300 (Table 2). Three (60%) of the five isolates possessed mupA (Table 2). The three mupA-positive isolates, all from the standard group, also demonstrated high-level resistance (>1,024 μg/ml) by Etest. Of note, two of the five clinical isolates were from subjects in the same training company.
TABLE 2.
Genotypic chlorhexidine resistance for individual subjects
| Subjecta | Study group | Specimen type | Time to isolate collection (days) | Isolate collection date | PFGE type | mupAb | Chlorhexidine MIC (μg/ml) |
|---|---|---|---|---|---|---|---|
| A | Chlorhexidine | Clinical | 49 | October 2010 | USA300 | No | 2 |
| B | Chlorhexidine | Clinical | 96 | September 2011 | USA300 | No | 2 |
| C | Standard | Clinical | 42 | March 2011 | USA300 | Yes | 4 |
| D | Standard | Clinical | 42 | March 2011 | USA300 | Yes | 4 |
| E | Standard | Clinical | 6 | September 2011 | USA300 | Yes | 2 |
| D | Standard | Colonizing | 42 | March 2011 | USA300 | Yes | 2 |
| F | Standard | Colonizing | 38 | July 2010 | USA300 | No | 1 |
| G | Standard | Colonizing | 17 | July 2010 | USA300 | No | 2 |
| H | Enhanced standard | Colonizing | 38 | July 2010 | USA300 | No | 1 |
| I | Chlorhexidine | Colonizing | 82 | September 2011 | USA300 | No | 2 |
Subjects C and D were from the same training company, and subjects B and I were from the same training company.
All isolates with mupA demonstrated high-level resistance (>1,024 μg/ml) by Etest.
Among the 283 SSTI cases, abscess (210 cases [74.2%]) and cellulitis (138 cases [48.8%]) were the most common clinical diagnoses, and many subjects developed more than one infection (104 cases [36.7%]). The most common site of infection was the lower extremities (126 cases [44.5%]). The time from training start to clinical presentation for MRSA SSTIs did not differ among the groups, and clinical presentation occurred around week 8 to 9 of training.
Analysis of colonizing MRSA isolates.
Anterior nares samples were obtained from 1,200 of the 1,203 SSTI subjects; of these, 265 samples (22.1%) yielded MRSA, i.e., 63 from the standard group, 97 from the enhanced standard group, and 105 from the chlorhexidine group. We also assessed nasal colonization in 1,712 control subjects; among these, 73 samples (4.3%) yielded MRSA, including 28 from the standard group, 19 from the enhanced standard group, and 26 from the chlorhexidine group. The total number of colonizing nasal isolates was 338, of which 274 (81.1%) were available for molecular analysis. No difference across study groups in the distribution of isolates available for testing was observed, and isolates were recovered throughout the study period.
Among colonizing MRSA isolates, there were no differences in the prevalence of qacA/B in the chlorhexidine group versus the standard and enhanced standard groups combined (0.9% versus 2.4%; P = 0.65). Analysis of the 274 colonizing MRSA isolates revealed five (1.8%) that were positive for qacA/B, i.e., three (4.1%) from the standard group, one (1.0%) from the enhanced standard group, and one (0.9%) from the chlorhexidine group. In broth dilution testing of these five colonizing isolates, three of the isolates, i.e., two from the standard group and one from the chlorhexidine group, had a chlorhexidine MIC of 2 μg/ml. The remaining two, one each from the standard and enhanced standard groups, had a chlorhexidine MIC of 1 μg/ml. All five isolates were USA300. Among these five isolates, mupA was detected in only one isolate, from a subject who also contributed a clinical chlorhexidine-resistant isolate (Table 2); the isolate demonstrated high-level resistance (>1,024 μg/ml) by Etest.
Antimicrobial susceptibilities.
We evaluated the association between qacA/B-positive MRSA isolates and resistance to commonly prescribed antimicrobials (Table 3). Most clinical and colonizing qacA/B-positive MRSA isolates were susceptible to most agents. Among the chlorhexidine-resistant MRSA isolates, resistance to ciprofloxacin and erythromycin was observed for both clinical and colonizing isolates; however, the number of isolates was small.
TABLE 3.
Genotypic chlorhexidine resistance by antimicrobial resistance
| Antibiotic and phenotype | No. (%) |
|||
|---|---|---|---|---|
| Clinical isolates (n = 341) |
Colonizing isolates (n = 274) |
|||
| qacA/B negative (n = 336) | qacA/B positive (n = 5) | qacA/B negative (n = 269) | qacA/B positive (n = 5) | |
| Ciprofloxacina | ||||
| Susceptible | 216 (100.0) | 0 (0) | 179 (100.0) | 0 (0) |
| Resistant | 120 (96.0) | 5 (4.0) | 90 (94.7) | 5 (5.3) |
| Clindamycinb | ||||
| Susceptible | 302 (98.4) | 5 (1.6) | 225 (97.9) | 5 (2.1) |
| Resistant | 34 (100.0) | 0 (0) | 44 (100.0) | 0 (0) |
| Daptomycin | ||||
| Susceptible | 335 (98.5) | 5 (1.5) | 269 (98.2) | 5 (1.8) |
| Resistant | 0 (0) | 0 (0) | 0 (0) | 0 (0) |
| Erythromycin | ||||
| Susceptible | 35 (100.0) | 0 (0) | 32 (100.0) | 0 (0) |
| Resistant | 301 (98.4) | 5 (1.6) | 237 (97.9) | 5 (2.0) |
| Gentamicin | ||||
| Susceptible | 334 (98.5) | 5 (1.5) | 268 (98.2) | 5 (1.8) |
| Resistant | 1 (100.0) | 0 (0) | 1 (100.0) | 0 (0) |
| Linezolid | ||||
| Susceptible | 335 (98.5) | 5 (1.5) | 269 (98.2) | 5 (1.8) |
| Resistant | 0 (0) | 0 (0) | 0 (0) | 0 (0) |
| Rifampin | ||||
| Susceptible | 335 (98.5) | 5 (1.5) | 268 (98.2) | 5 (1.8) |
| Resistant | 1 (100.0) | 0 (0) | 0 (0) | 0 (0) |
| Tetracycline | ||||
| Susceptible | 324 (98.5) | 5 (1.5) | 246 (98.0) | 5 (2.0) |
| Resistant | 12 (100.0) | 0 (0) | 23 (100.0) | 0 (0) |
| Trimethoprim-sulfamethoxazole | ||||
| Susceptible | 336 (98.5) | 5 (1.5) | 268 (98.2) | 5 (1.8) |
| Resistant | 0 (0) | 0 (0) | 1 (100.0) | 0 (0) |
P < 0.01 by Fisher's exact test for both clinical and colonizing isolates.
Twenty-nine (10.0%) of the 290 clinical isolates tested and 28 (12.4%) of the 225 colonizing isolates tested showed inducible clindamycin resistance.
DISCUSSION
In the context of a community-based, cluster-randomized, controlled trial, during which more than 10,000 soldiers were issued chlorhexidine, we found no association between extended chlorhexidine use and the prevalence of chlorhexidine-resistant MRSA isolates. Overall, the prevalence of chlorhexidine resistance during the 2-year period was low (1.6%), and isolation of resistant isolates did not seem to increase over time. Furthermore, 70% of chlorhexidine-resistant isolates were from subjects in groups that did not receive chlorhexidine.
These findings are similar to those observed by Fritz et al. (25). They found no significant increase in qacA/B acquisition in their investigation, which involved randomly assigning 258 subjects to receive 5 days of 4% chlorhexidine antiseptic wash (25). Similarly, during a study that involved the use of chlorhexidine-impregnated cloths thrice weekly over a 6-week period, Johnson et al. failed to detect any incident infections with chlorhexidine-resistant strains (24). Additionally, low prevalence rates of chlorhexidine-resistant isolates have been reported for MRSA isolates obtained from the global U.S. military network (0.9%) (23) and U.S. nursing home residents (0.6%) (21). As with other community-based interventions that have assessed the impact of chlorhexidine use on the development of resistance, the periods of use and/or observation might have been too brief to capture the emergence of chlorhexidine-resistant MRSA strains.
These findings are in contrast to those observed in the hospital setting, where the prevalence of qacA/B among clinical MRSA isolates may be as high as 80% (33–35). In Taiwan, the prevalence of chlorhexidine-resistant MRSA strains increased from 1.7% in 1990 to 47% in 2005 (36). Moreover, the prevalence of qacA/B in strains of MRSA colonizing health care workers appears to be rising (37). Additional studies to monitor chlorhexidine resistance in the hospital setting, where chlorhexidine is increasingly being used for daily bathing of patients, are needed.
The emergence of chlorhexidine resistance among MRSA isolates, whether clinical or colonizing, has implications for prevention and control efforts. In the hospital setting, long-term chlorhexidine use and the presence of qacA/B genes have been associated with decolonization failure and the spread of resistant strains. In a case-control study, Lee et al. found that the presence of qacA/B genes in combination with mupirocin resistance independently predicted failure of MRSA decolonization (20). In an investigation employing chlorhexidine to prevent MRSA transmission, Batra et al. found that the chlorhexidine intervention was effective only for patients who lacked chlorhexidine resistance genes (qacA/B) (18). Future MRSA prevention strategies that involve widespread use of chlorhexidine over extended periods should incorporate long-term surveillance for the emergence of chlorhexidine-resistant strains.
Genotypic resistance to chlorhexidine is indicated by the presence of qacA/B and smr genes, which encode drug efflux proteins that confer high-level and low-level S. aureus determinants (38, 39). However, chlorhexidine MICs have also been reported as indicators of decreasing susceptibility (36, 37). The challenges with this method are the absence of clear CLSI breakpoints, variable assays, and the fact that, while correlation of elevated MICs (>4 μg/ml) with the presence of qacA/B genes has been demonstrated (22), sometimes they are poorly correlated (21, 23). In our study, two of the qacA/B-positive isolates (20%) had an MIC of 4 μg/ml, both isolates from subjects in the standard group. Six of the isolates had an MIC of 2 μg/ml, and two had an MIC of 1 μg/ml. McGann et al. found all of the qacA/B-positive isolates in their study to have an MIC of 2 μg/ml (23).
We observed that the presence of qacA/B was associated with resistance to ciprofloxacin. qacA/B may share mobile genetic elements with other antibiotic resistance genes (40). Indeed, chlorhexidine resistance is more common in MRSA than in methicillin-sensitive S. aureus (MSSA) (41). Our finding is similar to other reports of antibiotic resistance associated with qacA/B (34, 37, 42). This observation may hint at the presence of another efflux-mediated resistance gene present in our isolates (perhaps norA) (42). Interestingly, all of our isolates harboring qacA/B were of the same lineage (USA300). Specific MRSA strains with associations with qacA/B have been reported, but no such associations have been noted in the United States (18, 35, 43).
Our study has several strengths. First, our large-scale, field-based, cluster-randomized trial among trainees at high risk for MRSA colonization and infection presented a unique opportunity to evaluate the emergence of chlorhexidine-resistant MRSA. Over the course of the 2-year study, nearly 625 gallons of chlorhexidine were distributed to over 10,000 trainees, creating an opportunity for evolutionary pressure and for the development and detection of resistant isolates. Second, our closed study population and unified health care network allowed us to obtain and to evaluate almost all MRSA clinical isolates collected from study subjects. Third, we collected nasal specimens from participants with and without clinical infections. Through this broad sampling distribution, we still observed low rates of chlorhexidine resistance among MRSA isolates not associated with clinical disease.
Even with the rigorous study design, our study has several limitations. First, the MRSA isolates evaluated for chlorhexidine resistance were obtained from trainees presenting to the TMC with SSTIs or noninfectious conditions. The prevalence of chlorhexidine resistance in the overall recruit population is not known. Second, due to the nature of the military training, we were unable to obtain baseline or terminal (at the end of training) colonization cultures from individual study participants. Such data might have helped us estimate the rate of qacA/B acquisition longitudinally and determine whether qacA/B was associated with chlorhexidine exposure or a chlorhexidine-resistant strain was introduced by a recruit upon entry. Third, due to limitations imposed by military training requirements, we were unable to capture data on individual levels of adherence to the once-weekly chlorhexidine shower, and we were able to assess only nasal colonization. However, a subset of subjects enrolled in the study completed a questionnaire assessing adherence to the prevention strategies, including chlorhexidine use. The majority (85.7%) of subjects assigned to the chlorhexidine group reported receiving the soap for use and 71.2% reported using it at least weekly, with an additional 11.3% reporting biweekly use. Although this represents fairly good adherence to the study intervention and is similar to findings from other studies that employed chlorhexidine (16, 25), we recognize that these are self-reported rates from a sample of the study population. Although a correlation between the presence of qacA/B and elevated MICs has been demonstrated, this correlation is not fully understood and the clinical implications of elevated MICs need to be further elucidated.
In summary, we found that extensive use of chlorhexidine in a community-based study conducted in a high-risk population was not associated with the emergence of chlorhexidine-resistant MRSA. Nevertheless, as MRSA SSTIs continue to cause morbidity in the community setting and chlorhexidine continues to be an integral component of prevention strategies, surveillance for acquired resistance is needed, particularly in high-risk settings.
ACKNOWLEDGMENTS
We thank the study team of clinical research coordinators, laboratory personnel, and data management staff members whose efforts made this project possible.
This work was supported by the Infectious Disease Clinical Research Program, a Department of Defense (DoD) program executed through the Uniformed Services University. This project has been funded with federal funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH), through an interagency agreement (grant Y1-AI-5072). Additional funding was provided by the Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases, Division of Healthcare Quality Promotion, through an interagency agreement (grant 09FED914272 to M.W.E.), and by the DoD Global Emerging Infections Surveillance program (grant C0366-11-HS to M.W.E.).
We have no financial, consultant, institutional, or other relationships that would constitute a conflict of interest.
The content of this publication is the sole responsibility of the authors and does not necessarily reflect the views or policies of the NIH, the Department of Health and Human Services, the DoD, or the Departments of the Army, Navy, or Air Force. Mention of trade names, commercial products, or organizations does not imply endorsement by the U.S. Government.
Footnotes
Published ahead of print 19 May 2014
REFERENCES
- 1.Hersh AL, Chambers HF, Maselli JH, Gonzales R. 2008. National trends in ambulatory visits and antibiotic prescribing for skin and soft-tissue infections. Arch. Intern. Med. 168:1585–1591. 10.1001/archinte.168.14.1585 [DOI] [PubMed] [Google Scholar]
- 2.Pallin DJ, Egan DJ, Pelletier AJ, Espinola JA, Hooper DC, Camargo CA., Jr 2008. Increased US emergency department visits for skin and soft tissue infections, and changes in antibiotic choices, during the emergence of community-associated methicillin-resistant Staphylococcus aureus. Ann. Emerg. Med. 51:291–298. 10.1016/j.annemergmed.2007.12.004 [DOI] [PubMed] [Google Scholar]
- 3.Talan DA, Krishnadasan A, Gorwitz RJ, Fosheim GE, Limbago B, Albrecht V, Moran GJ, EMERGEncy ID Net Study Group 2011. Comparison of Staphylococcus aureus from skin and soft-tissue infections in US emergency department patients, 2004 and 2008. Clin. Infect. Dis. 53:144–149. 10.1093/cid/cir308 [DOI] [PubMed] [Google Scholar]
- 4.Klein E, Smith DL, Laxminarayan R. 2009. Community-associated methicillin-resistant Staphylococcus aureus in outpatients, United States, 1999–2006. Emerg. Infect. Dis. 15:1925–1930. 10.3201/eid1512.081341 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Kazakova SV, Hageman JC, Matava M, Srinivasan A, Phelan L, Garfinkel B, Boo T, McAllister S, Anderson J, Jensen B, Dodson D, Lonsway D, McDougal LK, Arduino M, Fraser VJ, Killgore G, Tenover FC, Cody S, Jernigan DB. 2005. A clone of methicillin-resistant Staphylococcus aureus among professional football players. N. Engl. J. Med. 352:468–475. 10.1056/NEJMoa042859 [DOI] [PubMed] [Google Scholar]
- 6.Aiello AE, Lowy FD, Wright LN, Larson EL. 2006. Methicillin-resistant Staphylococcus aureus among US prisoners and military personnel: review and recommendations for future studies. Lancet Infect. Dis. 6:335–341. 10.1016/S1473-3099(06)70491-1 [DOI] [PubMed] [Google Scholar]
- 7.Army Medical Surveillance Activity. 2011. Ambulatory clinic visits among members of active components, U.S. Armed Forces, 2010. MSMR 18:16–21 [PubMed] [Google Scholar]
- 8.Salgado CD, Farr BM, Calfee DP. 2003. Community-acquired methicillin-resistant Staphylococcus aureus: a meta-analysis of prevalence and risk factors. Clin. Infect. Dis. 36:131–139. 10.1086/345436 [DOI] [PubMed] [Google Scholar]
- 9.Milstone AM, Passaretti CL, Perl TM. 2008. Chlorhexidine: expanding the armamentarium for infection control and prevention. Clin. Infect. Dis. 46:274–281. 10.1086/524736 [DOI] [PubMed] [Google Scholar]
- 10.Campbell KM, Vaughn AF, Russell KL, Smith B, Jimenez DL, Barrozo CP, Minarcik JR, Crum NF, Ryan MA. 2004. Risk factors for community-associated methicillin-resistant Staphylococcus aureus infections in an outbreak of disease among military trainees in San Diego, California, in 2002. J. Clin. Microbiol. 42:4050–4053. 10.1128/JCM.42.9.4050-4053.2004 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Wootton SH, Arnold K, Hill HA, McAllister S, Ray M, Kellum M, LaMarre M, Lane ME, Chaitram J, Lance-Parker S, Kuehnert MJ. 2004. Intervention to reduce the incidence of methicillin-resistant Staphylococcus aureus skin infections in a correctional facility in Georgia. Infect. Control Hosp. Epidemiol. 25:402–407. 10.1086/502413 [DOI] [PubMed] [Google Scholar]
- 12.Miller LG, Tan J, Eells SJ, Benitez E, Radner AB. 2012. Prospective investigation of nasal mupirocin, hexachlorophene body wash, and systemic antibiotics for prevention of recurrent community-associated methicillin-resistant Staphylococcus aureus infections. Antimicrob. Agents Chemother. 56:1084–1086. 10.1128/AAC.01608-10 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Fritz SA, Hogan PG, Hayek G, Eisenstein KA, Rodriguez M, Epplin EK, Garbutt J, Fraser VJ. 2012. Household versus individual approaches to eradication of community-associated Staphylococcus aureus in children: a randomized trial. Clin. Infect. Dis. 54:743–751. 10.1093/cid/cir919 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Liu C, Bayer A, Cosgrove SE, Daum RS, Fridkin SK, Gorwitz RJ, Kaplan SL, Karchmer AW, Levine DP, Murray BE, Rybak MJ, Talan DA, Chambers HF. 2011. Clinical practice guidelines by the Infectious Diseases Society of America for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children. Clin. Infect. Dis. 52:e18–e55. 10.1093/cid/ciq146 [DOI] [PubMed] [Google Scholar]
- 15.Daum RS, Spellberg B. 2012. Progress toward a Staphylococcus aureus vaccine. Clin. Infect. Dis. 54:560–567. 10.1093/cid/cir828 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Whitman TJ, Herlihy RK, Schlett CD, Murray PR, Grandits GA, Ganesan A, Brown M, Mancuso JD, Adams WB, Tribble DR. 2010. Chlorhexidine-impregnated cloths to prevent skin and soft-tissue infection in Marine recruits: a cluster-randomized, double-blind, controlled effectiveness trial. Infect. Control Hosp. Epidemiol. 31:1207–1215. 10.1086/657136 [DOI] [PubMed] [Google Scholar]
- 17.Morrison SM, Blaesing CR, Millar EV, Chukwuma U, Schlett CD, Wilkins KJ, Tribble DR, Ellis MW. 2013. Evaluation of methicillin-resistant Staphylococcus aureus skin and soft-tissue infection prevention strategies at a military training center. Infect. Control Hosp. Epidemiol. 34:841–843. 10.1086/671278 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Batra R, Cooper BS, Whiteley C, Patel AK, Wyncoll D, Edgeworth JD. 2010. Efficacy and limitation of a chlorhexidine-based decolonization strategy in preventing transmission of methicillin-resistant Staphylococcus aureus in an intensive care unit. Clin. Infect. Dis. 50:210–217. 10.1086/648717 [DOI] [PubMed] [Google Scholar]
- 19.Skovgaard S, Larsen MH, Nielsen LN, Skov RL, Wong C, Westh H, Ingmer H. 2013. Recently introduced qacA/B genes in Staphylococcus epidermidis do not increase chlorhexidine MIC/MBC. J. Antimicrob. Chemother. 68:2226–2233. 10.1093/jac/dkt182 [DOI] [PubMed] [Google Scholar]
- 20.Lee AS, Macedo-Vinas M, Francois P, Renzi G, Schrenzel J, Vernaz N, Pittet D, Harbarth S. 2011. Impact of combined low-level mupirocin and genotypic chlorhexidine resistance on persistent methicillin-resistant Staphylococcus aureus carriage after decolonization therapy: a case-control study. Clin. Infect. Dis. 52:1422–1430. 10.1093/cid/cir233 [DOI] [PubMed] [Google Scholar]
- 21.McDanel JS, Murphy CR, Diekema DJ, Quan V, Kim DS, Peterson EM, Evans KD, Tan GL, Hayden MK, Huang SS. 2013. Chlorhexidine and mupirocin susceptibilities of methicillin-resistant Staphylococcus aureus from colonized nursing home residents. Antimicrob. Agents Chemother. 57:552–558. 10.1128/AAC.01623-12 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.McGann P, Kwak YI, Summers A, Cummings JF, Waterman PE, Lesho EP. 2011. Detection of qacA/B in clinical isolates of methicillin-resistant Staphylococcus aureus from a regional healthcare network in the eastern United States. Infect. Control Hosp. Epidemiol. 32:1116–1119. 10.1086/662380 [DOI] [PubMed] [Google Scholar]
- 23.McGann P, Milillo M, Kwak YI, Quintero R, Waterman PE, Lesho E. 2013. Rapid and simultaneous detection of the chlorhexidine and mupirocin resistance genes qacA/B and mupA in clinical isolates of methicillin-resistant Staphylococcus aureus. Diagn. Microbiol. Infect. Dis. 77:270–272. 10.1016/j.diagmicrobio.2013.06.006 [DOI] [PubMed] [Google Scholar]
- 24.Johnson MD, Schlett CD, Grandits GA, Mende K, Whitman TJ, Tribble DR, Hospenthal DR, Murray PR. 2012. Chlorhexidine does not select for resistance in Staphylococcus aureus isolates in a community setting. Infect. Control Hosp. Epidemiol. 33:1061–1063. 10.1086/667744 [DOI] [PubMed] [Google Scholar]
- 25.Fritz SA, Hogan PG, Camins BC, Ainsworth AJ, Patrick C, Martin MS, Krauss MJ, Rodriguez M, Burnham CA. 2013. Mupirocin and chlorhexidine resistance in Staphylococcus aureus in patients with community-onset skin and soft tissue infections. Antimicrob. Agents Chemother. 57:559–568. 10.1128/AAC.01633-12 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 26.Ellis MW, Schlett CD, Millar EV, Wilkins KJ, Crawford KB, Morrison-Rodriguez SM, Pacha LA, Gorwitz RJ, Lanier JB, Tribble DR. 2014. Hygiene strategies to prevent methicillin-resistant Staphylococcus aureus skin and soft tissue infections: a cluster-randomized controlled trial among high-risk military trainees. Clin. Infect. Dis. 58:1540–1548. 10.1093/cid/ciu166 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Clinical and Laboratory Standards Institute. 2007. Performance standards for antimicrobial susceptibility testing; 16th informational supplement. M100-S17. Clinical and Laboratory Standards Institute, Wayne, PA [Google Scholar]
- 28.Fiebelkorn KR, Crawford SA, McElmeel ML, Jorgensen JH. 2003. Practical disk diffusion method for detection of inducible clindamycin resistance in Staphylococcus aureus and coagulase-negative staphylococci. J. Clin. Microbiol. 41:4740–4744. 10.1128/JCM.41.10.4740-4744.2003 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 29.Clinical and Laboratory Standards Institute. 2009. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically. Approved standard M07-A8 Clinical and Laboratory Standards Institute, Wayne, PA [Google Scholar]
- 30.Patel JB, Gorwitz RJ, Jernigan JA. 2009. Mupirocin resistance. Clin. Infect. Dis. 49:935–941. 10.1086/605495 [DOI] [PubMed] [Google Scholar]
- 31.Bannerman TL, Hancock GA, Tenover FC, Miller JM. 1995. Pulsed-field gel electrophoresis as a replacement for bacteriophage typing of Staphylococcus aureus. J. Clin. Microbiol. 33:551–555 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 32.McDougal LK, Steward CD, Killgore GE, Chaitram JM, McAllister SK, Tenover FC. 2003. Pulsed-field gel electrophoresis typing of oxacillin-resistant Staphylococcus aureus isolates from the United States: establishing a national database. J. Clin. Microbiol. 41:5113–5120. 10.1128/JCM.41.11.5113-5120.2003 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 33.Miyazaki NH, Abreu AO, Marin VA, Rezende CA, Moraes MT, Villas Boas MH. 2007. The presence of qacA/B gene in Brazilian methicillin-resistant Staphylococcus aureus. Mem. Inst. Oswaldo Cruz 102:539–540. 10.1590/S0074-02762007000400018 [DOI] [PubMed] [Google Scholar]
- 34.Vali L, Davies SE, Lai LL, Dave J, Amyes SG. 2008. Frequency of biocide resistance genes, antibiotic resistance and the effect of chlorhexidine exposure on clinical methicillin-resistant Staphylococcus aureus isolates. J. Antimicrob. Chemother. 61:524–532. 10.1093/jac/dkm520 [DOI] [PubMed] [Google Scholar]
- 35.Ho J, Branley J. 2012. Prevalence of antiseptic resistance genes qacA/B and specific sequence types of methicillin-resistant Staphylococcus aureus in the era of hand hygiene. J. Antimicrob. Chemother. 67:1549–1550. 10.1093/jac/dks035 [DOI] [PubMed] [Google Scholar]
- 36.Wang JT, Sheng WH, Wang JL, Chen D, Chen ML, Chen YC, Chang SC. 2008. Longitudinal analysis of chlorhexidine susceptibilities of nosocomial methicillin-resistant Staphylococcus aureus isolates at a teaching hospital in Taiwan. J. Antimicrob. Chemother. 62:514–517. 10.1093/jac/dkn208 [DOI] [PubMed] [Google Scholar]
- 37.Zhang M, O'Donoghue MM, Ito T, Hiramatsu K, Boost MV. 2011. Prevalence of antiseptic-resistance genes in Staphylococcus aureus and coagulase-negative staphylococci colonising nurses and the general population in Hong Kong. J. Hosp. Infect. 78:113–117. 10.1016/j.jhin.2011.02.018 [DOI] [PubMed] [Google Scholar]
- 38.Paulsen IT, Brown MH, Littlejohn TG, Mitchell BA, Skurray RA. 1996. Multidrug resistance proteins QacA and QacB from Staphylococcus aureus: membrane topology and identification of residues involved in substrate specificity. Proc. Natl. Acad. Sci. U. S. A. 93:3630–3635. 10.1073/pnas.93.8.3630 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 39.Paulsen IT, Skurray RA, Tam R, Saier MH, Jr, Turner RJ, Weiner JH, Goldberg EB, Grinius LL. 1996. The SMR family: a novel family of multidrug efflux proteins involved with the efflux of lipophilic drugs. Mol. Microbiol. 19:1167–1175. 10.1111/j.1365-2958.1996.tb02462.x [DOI] [PubMed] [Google Scholar]
- 40.Horner C, Mawer D, Wilcox M. 2012. Reduced susceptibility to chlorhexidine in staphylococci: is it increasing and does it matter? J. Antimicrob. Chemother. 67:2547–2559. 10.1093/jac/dks284 [DOI] [PubMed] [Google Scholar]
- 41.Mayer S, Boos M, Beyer A, Fluit AC, Schmitz FJ. 2001. Distribution of the antiseptic resistance genes qacA, qacB and qacC in 497 methicillin-resistant and -susceptible European isolates of Staphylococcus aureus. J. Antimicrob. Chemother. 47:896–897. 10.1093/jac/47.6.896 [DOI] [PubMed] [Google Scholar]
- 42.DeMarco CE, Cushing LA, Frempong-Manso E, Seo SM, Jaravaza TA, Kaatz GW. 2007. Efflux-related resistance to norfloxacin, dyes, and biocides in bloodstream isolates of Staphylococcus aureus. Antimicrob. Agents Chemother. 51:3235–3239. 10.1128/AAC.00430-07 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 43.Alam MM, Kobayashi N, Uehara N, Watanabe N. 2003. Analysis on distribution and genomic diversity of high-level antiseptic resistance genes qacA and qacB in human clinical isolates of Staphylococcus aureus. Microb. Drug Resist. 9:109–121. 10.1089/107662903765826697 [DOI] [PubMed] [Google Scholar]