Abstract
In a field-based trial among military trainees, personal hygiene measures, including chlorhexidine (CHG) body wash, did not prevent overall and methicillin-resistant Staphylococcus aureus (MRSA) skin and soft-tissue infections (SSTI). We conducted a secondary analysis of anterior nares cultures obtained during the trial to evaluate the impact of hygiene measures on Staphylococcus aureus colonization. A cluster-randomized trial for SSTI prevention was conducted among U.S. Army infantry trainees from May 2010 to January 2012. There were three study groups with incrementally increasing education- and hygiene-based components: standard (S), enhanced standard (ES), and CHG. Anterior nares cultures were obtained from participants to determine the prevalence of S. aureus colonization. A total of 1,706 participants (469 S, 597 ES, and 640 CHG) without SSTI were included in the colonization analysis. Of those randomized to the CHG group, 360 (56.3%) reported frequent use of body wash. Frequent use of body wash had no effect on overall S. aureus colonization (53.3% versus 56.8% among infrequent/nonusers; P = 0.25). MRSA colonization prevalence was marginally lower among frequent users (2.5% versus 4.7%; P = 0.07). In multivariable analysis, the odds of MRSA colonization were lower among frequent users (odds ratio [OR], 0.36; 95% confidence interval [CI], 0.16 to 0.77). This CHG-associated reduction was not observed when comparing colonization with USA300 to that with non-USA300 types (OR, 0.59; 95% CI, 0.06 to 5.76). Frequent use of CHG body wash was associated with a reduction in MRSA nasal colonization among high-risk military trainees. Topical chlorhexidine may contribute to MRSA SSTI prevention by reducing colonization. However, further studies evaluating the pathogenesis of SSTI are needed. (This study has been registered at ClinicalTrials.gov under registration no. NCT01105767).
INTRODUCTION
Skin and soft-tissue infections (SSTI), especially those caused by methicillin-resistant Staphylococcus aureus (MRSA), have become increasingly common in communities. Individuals in congregate settings (e.g., athletes, inmates, and military personnel) are known to be at increased risk for SSTI (1–3). Among military personnel, infection rates are highest in trainees (4, 5). Because SSTI can interrupt training cycles and compromise operational readiness, effective SSTI prevention strategies for military populations are critically needed.
In the absence of a vaccine for Staphylococcus aureus, hygiene-based measures (e.g., hand washing, appropriate wound care, environmental disinfection, and patient education) comprise the current strategy for stemming SSTI outbreaks and preventing new cases of disease (1, 3, 6). As colonization has a demonstrated role in the pathogenesis and transmission of S. aureus, elimination of the carrier state with topical and systemic agents also has been employed as a prevention strategy (7–10). Nevertheless, the optimal method to prevent SSTI in congregate settings remains unknown.
To date, two field-based randomized controlled trials for SSTI prevention, both using chlorhexidine gluconate (CHG), have been conducted among U.S. military trainees (11, 12). Among recruits attending Officer Candidate School at Marine Corps Base, Quantico, Virginia, a thrice-weekly application of CHG-impregnated body cloths over a 6-week period did not reduce rates of SSTI (11). With respect to colonization, however, an analysis of nasal/axillary swabs showed a significant reduction in MRSA acquisition rates among CHG-randomized participants compared to the control (3.3% versus 6.5%; P = 0.004) (13). More importantly, a reduction in colonization was observed for USA300, the predominant community-associated MRSA strain (13, 14).
In May 2010, a three-group, hygiene-based cluster-randomized trial was initiated among U.S. Army infantry trainees at Fort Benning, Georgia (12). In addition to receiving enhanced education on SSTI and MRSA awareness and prevention, participants in one arm of the trial were instructed to use a CHG-based body wash once weekly during training and were surveyed regarding the frequency of use. As a secondary objective of the trial, nasal swabs were collected to assess the impact on Staphylococcus aureus colonization. Here, we evaluate the association between frequent body wash use and S. aureus nasal colonization and consider the implications for future SSTI prevention strategies among high-risk populations.
MATERIALS AND METHODS
Study design.
In brief, we conducted a three-group, field-based, cluster-randomized trial to determine the effectiveness of hygiene-based measures in preventing SSTI among military trainees (12). We then conducted a secondary analysis of anterior nares cultures obtained during the trial to evaluate the impact of hygiene measures on Staphylococcus aureus colonization.
Study participants and setting.
The study population was comprised of U.S. Army soldiers undergoing 14-week infantry training at Fort Benning, Georgia. The population was all male, between 17 and 42 years of age, ethnically diverse, and in generally good physical condition.
Interventions.
There were three study groups. Each was comprised of two battalions of trainees (∼10,000 soldiers per group). Each group (standard [S], enhanced standard [ES], and CHG) was assigned an intervention consisting of incrementally increasing hygiene measures (12). A critical component of the CHG group was that trainees received chlorhexidine antiseptic body wash (4% chlorhexidine gluconate; Hibiclens; Mölnlycke Heath Care, Norcross, GA) to use with a wash cloth after using their personal soap during an additional once-weekly shower. Trainees were provided with verbal and written/graphic instructions for use and were instructed to use the body wash for the entire training period.
Randomization.
Training battalions were the unit of randomization, and platoons were the unit of analysis. Two battalions each were assigned by computer-generated random numbers to one of the three study groups. Each platoon received the intervention assigned to its respective battalion at the study start. Investigators had no control over individual trainee battalion assignment or battalion training schedules.
Eligibility.
Enrollment began on 7 May 2010, and follow-up was completed on 20 January 2012. All trainees during this period comprised the eligible study population. All eligible trainees underwent a group-based informed consent process for the hygiene measures.
Enrollment and data collection.
For the colonization endpoint, we recruited a convenience sample of infantry trainees who presented to the Troop Medical Clinic (TMC) for noninfectious conditions (e.g., musculoskeletal injury). Specifically, trainees with SSTI were excluded. After informed consent, participants completed a risk factor questionnaire and underwent anterior nares screening culture (BD BBL CultureSwab; BD Diagnostic, Sparks, MD). The questionnaires assessed SSTI risk factors, hygiene practices, and adherence to the intervention components (i.e., frequency of use of CHG body wash). Platoon characteristics were obtained from the one-station unit training (OSUT) command.
Laboratory methods.
Anterior nares specimens were placed in 5 ml of tryptic soy broth (TSB) supplemented with 6.5% NaCl (BBL, BD Diagnostic, Sparks MD) and were incubated for 18 to 24 h at 37°C. After incubation, an aliquot of broth was plated onto mannitol salt agar (MSA). Mannitol-fermenting colonies were isolated and plated onto Trypticase soy agar with 5% sheep's blood and incubated overnight. S. aureus isolates were identified based on colony morphology, Gram stain, latex agglutination (Staphaurex; Remel, Lenexa, KS), and slide catalase testing. All S. aureus isolates underwent identification and susceptibility testing using a Microscan WalkAway 96 (Dade Behring Inc., Deerfield, IL) according to Clinical and Laboratory Standards Institutes (CLSI) methods (15). Additionally, all MRSA isolates underwent typing with pulsed-field gel electrophoresis (PFGE) (16) and PCR to assess for resistance (17) and virulence genes (18). PFGE findings were resolved and analyzed using BioNumerics (Applied Math, Austin, TX). Laboratory personnel were blinded to randomization assignment.
Statistical analysis.
Based on survey responses and for the purposes of the analysis, trainees were categorized as frequent (daily/weekly) or infrequent (every other week)/nonusers of the body wash. Differences in trainee characteristics were assessed using proportions for categorical variables and medians and ranges for skewed continuous variables. Bivariate associations of potential risk factors for colonization were assessed using P < 0.10 as a criterion for inclusion in the final model. To assess the impact of CHG on colonization, we performed multivariate logistic regression with adjustment for within-platoon and within-class correlation using generalized estimating equations (GEE) (19). Odds ratios (OR) and 95% confidence intervals (CI) are reported. Analyses were performed using SAS, version 9.3 (SAS Institute, Cary, NC).
Human subjects.
The Uniformed Services University Infectious Diseases Institutional Review Board approved the investigation.
RESULTS
Participant characteristics.
A total of 1,706 trainees (382 platoons) were included in the colonization analysis. By study group, the distribution of participants was the following: S, 469 trainees (121 platoons); ES, 597 trainees (130 platoons); CHG, 640 trainees (131 platoons).
Reported CHG use.
Surveys were completed by all 1,706 trainees. With respect to the use of body wash, all trainees in the S and ES groups reported never having used the product. Among trainees in the CHG group, 210 (32.8%) reported never having used it, and 70 (10.9%) reported using it every other week. A total of 360 (56.3%) trainees in the CHG group reported weekly (n = 325; 50.8%) or daily (n = 35; 5.5%) use, which we categorized as frequent use for the analysis.
The characteristics of trainees, stratified by frequent versus infrequent/no use of body wash, are described in Table 1. A higher proportion of those reporting frequent use of body wash were in phase I (weeks 1 to 9) of training (77.5% versus 64%; P < 0.001), were swabbed in the spring/summer months (71.1% versus 57.6%; P < 0.001), washed towels daily or several times per week (49.5% versus 41.2%; P = 0.004), and used hand sanitizer four or more times per day (83.6% versus 77.7%; P = 0.02). The groups did not differ in the reported frequency of showering (two or more times per day, 31.9% versus 31.4%; P = 0.86) or washing their uniform (62.5% versus 58.1%; P = 0.13). A higher proportion of subjects in the infrequent/no use group came from a platoon where an SSTI case was diagnosed prior to their enrollment and swab collection (55.1% versus 46.7%; P = 0.005).
TABLE 1.
Characteristics of trainees by reported use of CHG body wash
| Parameter | Value for reported frequency of body wash use |
P valuea | |
|---|---|---|---|
| Biweekly/never (n = 1,346) | Daily/weekly (n = 360) | ||
| No. of platoons | 345 | 114 | |
| Range of no. of enrolled trainees per platoon | 1–23 | 1–13 | |
| Mean age (SD), yr | 20.9 (3.6) | 20.6 (3.6) | 0.129 |
| No. (%) of samples by wk of training at time of swab | |||
| 1–3 | 274 (20.4) | 112 (31.1) | <0.001 |
| 4–6 | 303 (22.5) | 83 (23.1) | |
| 7–9 | 284 (21.1) | 84 (23.3) | |
| 10–12 | 426 (31.7) | 75 (20.8) | |
| 13–14 | 58 (4.3) | 6 (1.7) | |
| No. (%) of samples by season of swab | |||
| Spring | 337 (25.0) | 142 (39.4) | <0.001 |
| Summer | 438 (32.5) | 114 (31.7) | |
| Fall | 431 (32.0) | 47 (13.1) | |
| Winter | 140 (10.4) | 57 (15.8) | |
| No. (%) of samples by season of training start | |||
| Spring | 396 (29.4) | 145 (40.3) | <0.001 |
| Summer | 514 (38.2) | 86 (23.9) | |
| Fall | 166 (12.3) | 11 (3.1) | |
| Winter | 270 (20.1) | 118 (32.8) | |
| Presence of SSTI case in platoon prior to enrollment (no. [%]) | |||
| No | 605 (44.9) | 192 (53.3) | 0.005 |
| Yes | 741 (55.1) | 168 (46.7) | |
| Frequency of hand sanitizer use, per day (no. [%]) | |||
| ≤3 times | 300 (22.3) | 59 (16.4) | 0.015 |
| ≥4 times | 1,043 (77.7) | 300 (83.6) | |
| Frequency of showers, per day (no. [%]) | |||
| ≤1 | 920 (68.6) | 245 (68.1) | 0.856 |
| ≥2 | 422 (31.4) | 115 (31.9) | |
| No. (%) of trainees who shared towels during training | |||
| Ever | 75 (5.6) | 11 (3.1) | 0.052 |
| Never | 1,269 (94.4) | 349 (96.9) | |
| Frequency of washing towels (no. [%]) | |||
| ≤1 time/week or never | 789 (58.8) | 181 (50.4) | 0.004 |
| Daily/several times per week | 553 (41.2) | 178 (49.5) | |
| Frequency of washing uniform (no. [%]) | |||
| ≤1 time/week or never | 560 (41.9) | 135 (37.5) | 0.131 |
| Daily/several times per week | 776 (58.1) | 225 (62.5) | |
| Study group (no. [%]) | |||
| Standard | 469 (34.8) | 0 (0) | <0.001 |
| Enhanced standard | 597 (44.4) | 0 (0) | |
| Chlorhexidine | 280 (20.8) | 360 (100) | |
Difference in proportions for categorical variables and comparison of means for continuous variables.
Colonization.
Of 1,706 swabs, 956 (56%) were positive for S. aureus, and 72 (7.5%) of these were MRSA (Table 2). The prevalence of S. aureus colonization did not differ between those reporting frequent versus infrequent/no use (53.3% and 56.8%, respectively; P = 0.25). Prevalence estimates did not differ by the season in which the swab was collected (P = 0.18), by frequency of use of hand sanitizers (P = 0.2), by frequency of showers (P = 0.28), or by frequency of washing of towels (P = 0.09). S. aureus colonization prevalence was higher among those in a platoon where at least one case of SSTI had been diagnosed prior to the collection of the swab (59.4% versus 52.2%; P = 0.003) and among those reporting a higher frequency of washing their uniform (58.1% versus 53.1%; P = 0.04).
TABLE 2.
Univariate analysis of S. aureus and MRSA colonization
| Parameter | Total no. of samples (n = 1,706) | Value fora: |
|||
|---|---|---|---|---|---|
|
S. aureus |
MRSA |
||||
| No. (%) | P value | No. (%) | P value | ||
| Total | 956 (56.0) | 72 (4.2) | |||
| Use of body wash | |||||
| Biweekly/never | 1,346 | 764 (56.8) | 0.245 | 63 (4.7) | 0.068 |
| Weekly/daily | 360 | 192 (53.3) | 9 (2.5) | ||
| Wk of training at time of swab | |||||
| 1–3 | 386 | 209 (54.1) | 0.275 | 19 (4.9) | 0.486 |
| 4–6 | 386 | 209 (54.1) | 13 (3.4) | ||
| 7–9 | 368 | 209 (56.8) | 16 (4.3) | ||
| 10–12 | 501 | 298 (59.5) | 19 (3.8) | ||
| 13–14 | 64 | 31 (48.4) | 5 (7.8) | ||
| Season of swab | |||||
| Spring | 479 | 255 (53.2) | 0.182 | 23 (4.8) | 0.105 |
| Summer | 552 | 320 (58.0) | 30 (5.4) | ||
| Fall | 478 | 279 (58.4) | 15 (3.1) | ||
| Winter | 197 | 102 (51.8) | 4 (2.0) | ||
| Season of training start | |||||
| Spring | 541 | 310 (57.3) | 0.020 | 36 (6.7) | 0.005 |
| Summer | 600 | 354 (59.0) | 22 (3.7) | ||
| Fall | 177 | 101 (57.1) | 4 (2.3) | ||
| Winter | 388 | 191 (49.2) | 10 (2.6) | ||
| Presence of SSTI case in platoon prior to enrollment | |||||
| No | 797 | 416 (52.2) | 0.003 | 33 (4.1) | 0.878 |
| Yes | 909 | 540 (59.4) | 39 (4.3) | ||
| Frequency of hand sanitizer use, per day | |||||
| ≤3 times | 359 | 212 (59.1) | 0.197 | 17 (4.7) | 0.593 |
| ≥4 times | 1,343 | 742 (55.3) | 55 (4.1) | ||
| Frequency of showers, per day | |||||
| ≤1 | 1,165 | 664 (57.0) | 0.278 | 50 (4.3) | 0.852 |
| ≥2 | 537 | 291 (54.2) | 22 (4.1) | ||
| No. (%) of trainees who shared towels during training | |||||
| Ever | 86 | 55 (64.0) | 0.129 | 6 (7.0) | 0.193 |
| Never | 1,618 | 900 (55.6) | 66 (4.1) | ||
| Frequency of washing towels | |||||
| ≤1 time/week or never | 970 | 527 (54.3) | 0.093 | 38 (3.9) | 0.457 |
| Daily/several times per week | 731 | 427 (58.4) | 34 (4.6) | ||
| Frequency of washing uniform | |||||
| ≤1 time/week or never | 695 | 369 (53.1) | 0.040 | 26 (3.7) | 0.391 |
| Daily/several times per week | 1,001 | 582 (58.1) | 46 (4.6) | ||
| Study group | |||||
| Standard | 469 | 266 (56.7) | 0.425 | 28 (6.0) | 0.071 |
| Enhanced standard | 597 | 344 (57.6) | 19 (3.2) | ||
| CHG (biweekly/never) | 640 | 346 (54.1) | 25 (3.9) | ||
Difference in proportions for categorical variables.
MRSA colonization prevalence was lower among those reporting frequent use (2.5% versus 4.7%; P = 0.07) (Table 2). However, these differences were not statistically significant. Estimates of MRSA colonization prevalence did not differ across levels among the various covariates that were evaluated.
Multivariate analysis.
The odds of S. aureus colonization did not differ between those reporting frequent versus infrequent/no use of body wash (OR, 0.91; 95% confidence interval [CI], 0.66 to 1.27) (Table 3). The odds of S. aureus colonization were higher among those individuals in platoons where at least one SSTI case had been diagnosed prior to the collection of the swab (OR, 1.28; 95% CI, 1.01 to 1.63). There was no association between S. aureus colonization prevalence and week of training at the time of swab (OR, 1.00; 95% CI, 0.97 to 1.03), frequency of hand sanitizer use (OR, 0.84; 95% CI, 0.67 to 1.06), frequency of washing towels (OR, 1.11; 95% CI, 0.89 to 1.38), or frequency of washing uniforms (OR, 1.13; 95% CI, 0.90 to 1.42).
TABLE 3.
Results of the multivariate logistic regression for S. aureus and MRSA colonization with adjustment for within-cluster correlation
| Characteristic |
S. aureus colonizationa (odds ratio [95% CI]) |
|
|---|---|---|
| Overall | MRSA | |
| Use of body wash | ||
| Biweekly/never | 1.00 | 1.00 |
| Daily/weekly | 0.91 (0.66, 1.27) | 0.36* (0.16, 0.77) |
| Study group | ||
| Standard (reference) | 1.00 | 1.00 |
| Enhanced standard | 0.95 (0.73, 1.24) | 0.53# (0.27, 1.04) |
| Chlorhexidine | 0.96 (0.69, 1.32) | 0.99 (0.50, 1.97) |
| Season of training start | ||
| Winter | 1.00 | 1.00 |
| Spring | 1.35# (1.00, 1.84) | 2.54* (1.19, 5.45) |
| Summer | 1.32# (0.98, 1.78) | 1.27 (0.58, 2.78) |
| Fall | 1.38# (0.97, 1.95) | 0.79 (0.29, 2.16) |
| Duration of training at the time of swab | ||
| Week n + 1 vs. n (n = 1, 2…,15) | 1.00 (0.97, 1.03) | 0.96 (0.89, 1.04) |
| Presence of SSTI case in platoon prior to enrollment | ||
| No | 1.00 | 1.00 |
| Yes | 1.28* (1.01, 1.62) | 1.34 (0.76, 2.34) |
| Frequency of hand sanitizer use, per day | ||
| ≤3 times | 1.00 | 1.00 |
| ≥4 times | 0.84 (0.67, 1.06) | 0.83 (0.46, 1.48) |
| Frequency of washing towels | ||
| ≤1 time/week or never | 1.00 | 1.00 |
| Daily/several times per week | 1.11 (0.89, 1.38) | 1.19 (0.65, 2.18) |
| Frequency of washing uniform | ||
| ≤1 time/week or never | 1.00 | 1.00 |
| Daily/several times per week | 1.13 (0.90, 1.42) | 1.05 (0.53, 2.06) |
*, P < 0.05; #, P < 0.1 and P > 0.05.
With regard to MRSA colonization, the odds of MRSA colonization were significantly lower among those reporting frequent versus infrequent/no use of body wash (OR, 0.36; 95% CI, 0.16 to 0.76) (Table 3). Participants who started training in the spring months were more likely to be colonized with MRSA than those who started in winter (OR, 2.54; 95% CI, 1.19 to 5.45). The odds of MRSA colonization did not differ among those individuals in platoons where at least one SSTI case had been diagnosed prior to the collection of the swab (OR, 1.34; 95% CI, 0.76 to 2.34). Furthermore, there was no association between MRSA colonization prevalence and week of training at the time of swab (OR, 0.96; 95% CI, 0.89 to 1.04), frequency of hand sanitizer use (OR, 0.83; 95% CI, 0.46 to 1.48), frequency of washing towels (OR, 1.19; 95% CI, 0.65 to 2.18), or frequency of washing uniforms (OR, 1.05; 95% CI, 0.53 to 2.06).
Molecular analysis.
Of the 72 MRSA isolates, 60 (83.3%) were available for PFGE. Of these, 33 (55%) were USA300, 14 (23.4%) were USA800, 5 (8.3%) were USA100, and 8 (13.3%) were other types (undistinguished) (Table 4). Among USA300 isolates, three (9.1%) were from trainees reporting frequent use of body wash, whereas among non-USA300 isolates, five (18.5%) had reported frequent use (P = 0.45).
TABLE 4.
Distribution of USA300 MRSA and non-USA300 colonization by frequency of body wash use
| Frequency of body wash use | No. of MRSA isolates with PFGE type (n = 60) |
P value | |||||
|---|---|---|---|---|---|---|---|
| USA300 | Non-USA300 |
Missing | |||||
| USA100 | USA800 | Other | All | ||||
| Never | 28 | 5 | 9 | 5 | 10 | ||
| Biweekly | 2 | 0 | 1 | 2 | 1 | ||
| Weekly | 3 | 0 | 4 | 1 | 1 | ||
| Biweekly/never | 30 (57.7) | 22 (42.3) | 0.448 (exact) | ||||
| Weekly/daily | 3 (37.5) | 5 (62.5) | |||||
In multivariate analysis, the odds of MRSA USA300 colonization did not vary by frequency of body wash use (OR, 0.74; 95% CI, 0.09 to 6.37), season (OR for spring, 1.52; 95% CI, 0.34 to 6.68), week of training (OR, 0.97; 95% CI, 0.83 to 1.13), frequency of hand sanitizer use (OR, 0.64; 95% CI, 0.16 to 2.50), frequency of washing towels (OR, 1.81; 95% CI, 0.51 to 6.37), or frequency of washing uniforms (OR, 0.65; 95% CI, 0.15 to 2.88) (Table 5).
TABLE 5.
Results of the multivariate logistic regression for MRSA USA300 colonization with adjustment for within-cluster correlation
| Characteristic | Value (odds ratio [95% CI]) |
|---|---|
| Use of body wash | |
| Biweekly/never | 1.00 |
| Daily/weekly | 0.74 (0.09, 6.37) |
| Study group | |
| Standard (reference) | 1.00 |
| Enhanced standard | 1.20 (0.32, 4.51) |
| Chlorhexidine | 0.58 (0.13, 2.59) |
| Season of training start | |
| Winter | 1.00 |
| Spring | 1.52 (0.34, 6.68) |
| Summer | 1.29 (0.25, 6.72) |
| Fall | 3.84 (0.17, 87.3) |
| Duration of training | |
| Week n + 1 vs. n (n = 1, 2…,15) | 0.97 (0.83, 1.13) |
| Presence of SSTI case in platoon prior to enrollment | |
| No | 1.00 |
| Yes | 1.12 (0.31, 4.06) |
| Frequency of hand sanitizer use, per day | |
| ≤3 times | 1.00 |
| ≥4 times | 0.64 (0.16, 2.5) |
| Frequency of washing towels | |
| ≤1 time/week or never | 1.00 |
| Daily/several times per week | 1.81 (0.51, 6.37) |
| Frequency of washing uniform | |
| ≤1 time/week or never | 1.00 |
| Daily/several times per week | 0.65 (0.15, 2.88) |
DISCUSSION
In the setting of a large-scale, field-based, cluster-randomized trial for SSTI prevention, frequent use of CHG-based body wash was associated with a reduction in MRSA nasal colonization among military trainees at high risk for MRSA colonization and disease. In contrast, there was no such reduction in overall S. aureus nasal colonization, which suggests that CHG and other commonly used agents for decolonization have differential effects on methicillin-resistant compared to methicillin-susceptible S. aureus (MSSA) strains (13). The CHG-associated reduction in MRSA nasal colonization is particularly noteworthy, because in the context of the larger trial in which this study was conducted, these same hygiene-based measures had no effect on rates of overall SSTI or MRSA SSTI (12).
The observed impact of chlorhexidine on MRSA colonization is consistent with that of another SSTI prevention trial among military recruits (13). In that study, conducted in a similar close-quartered training environment, routine application of CHG-based body wipes failed to prevent overall SSTI but appeared to delay the nasal and axillary acquisition of MRSA USA300. While the role of MRSA colonization in the pathogenesis of SSTI still is not clearly understood, these studies suggest that routine use of decolonization measures in high-risk, congregate populations contribute to the prevention of SSTI.
The ecology of S. aureus colonization at various anatomic sites is very likely dynamic and multifactorial, involving both host and microbial factors. This complex ecology has yet to be fully described. Nonnasal sites are colonized by MRSA (20–23). Significant differences in colonization patterns between MRSA and MSSA have been reported. For example, MRSA has been shown to more frequently colonize inguinal folds than the anterior nares, while MSSA has been shown to more frequently colonize the anterior nares (20, 21). Chlorhexidine use may impact these nonnasal anatomic sites and, subsequently, interfere with overall MRSA ecology.
The mechanism by which topical CHG body wash reduces MRSA nasal colonization is not known. It is possible that the application of CHG to body surfaces reduces the total burden of MRSA colonization in the host, thereby reducing the likelihood of the colonization of the nasal cavity. Alternatively, widespread use of CHG in a congregate setting may reduce the overall burden of MRSA colonization in the group. As person-to-person transmission is an important means by which MRSA is spread (9, 20, 22, 24, 25), CHG may confer protection by reducing the host reservoir for MRSA and thereby interrupting its transmission to noncolonized individuals. In our study, S. aureus colonization was associated with being in a platoon where a case of SSTI had recently occurred. Routine widespread use of decolonization measures over a prolonged duration might be necessary to minimize infection risk. Additional measures might also need to be applied; the application of intranasal mupirocin in conjunction with CHG-based skin cleansers has been shown to be effective in other community-based studies (8, 9, 22).
The presence and persistence of MRSA on environmental surfaces has been described previously (26) and may represent an important reservoir and means of transmission of MRSA in congregate settings. While uniform cleaning of environmental surfaces with standard EPA-registered agents was a standard component of the trial (27), we did not collect samples from common-touch surfaces (e.g., countertops, wrestling mats, and weight benches) to assess MRSA prevalence on nonhuman reservoirs. The extent to which MRSA contamination of environmental surfaces contributes to the risk of SSTI is not known. The complex epidemiology of SSTI likely is explained by a dynamic interplay of host, pathogen, and environmental factors (25). Understanding these factors and their role in the pathogenesis of SSTI is critical to developing effective prevention strategies.
There are several strengths to this study. First, it was conducted in the context of a cluster-randomized controlled trial in a population known to be at increased risk for MRSA colonization and disease. In a trial of this design and magnitude, the biases associated with participant recruitment and sampling likely were minimal. Second, the study was conducted in a military setting, where the supervisory structure between drill sergeants and trainees, the schedule of training activities, and the access and utilization of health care is uniform and highly regimented. Lastly, the reported rates of CHG adherence were similar to those of other community-based studies for SSTI prevention (8, 9, 11).
There are limitations to our study. First, we defined colonization as the isolation of S. aureus from a single nasal culture. As noted, S. aureus/MRSA colonizes other body sites (e.g., axilla, groin, and perineum), but we restricted sampling to the nose. Second, the frequency of the use of body wash was obtained through self-administered trainee surveys. It is possible that some trainees overestimated the frequency of use because of their inability to recall or to provide what they perceived to be the desirable response. That said, overestimates of CHG use would in fact underestimate its effectiveness on reducing MRSA colonization, and the true impact may be greater than what we reported. Third, due to logistical issues, colonization swabs were collected from trainees presenting to the TMC for noninfectious conditions rather than from a random sample of trainees from all platoons. It is unlikely, however, that the epidemiology of S. aureus colonization would differ between the groups that we sampled versus the groups that we did not. Fourth, we did not collect information on antibiotic use. Finally, our estimates of colonization are derived from a cross-sectional study design. It is possible that colonization occurred below the limits of detection and/or that we failed to capture the impact of CHG on the dynamics of colonization (i.e., colonization of reduced duration).
In conclusion, we report that frequent use of CHG body wash was associated with reduced MRSA nasal colonization among military recruits at high risk for colonization and disease. Although these same measures failed to prevent SSTI, the magnitude of the impact on colonization suggests there is still a role for CHG and other decolonizing agents in community-based strategies for SSTI prevention. Longitudinal studies are needed to better understand MRSA colonization and transmission dynamics and to understand their relation to disease pathogenesis, particularly in congregate populations of otherwise healthy individuals.
ACKNOWLEDGMENTS
We are indebted to the study team of clinical research coordinators, laboratory personnel, and data management staff for their dedication to the project. The views expressed in this paper are those of the authors and do not necessarily represent the views of the Uniformed Services University of the Health Sciences, the Department of Defense, or other federal agencies.
We have no conflicts of interest to report.
The work was supported by the Infectious Disease Clinical Research Program (IDCRP), a Department of Defense program executed through the Uniformed Services University of the Health Sciences. This project has been funded in whole or in part with federal funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH), under Interagency Agreement 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 (NCEZID-DHQP; Interagency Agreement 09FED914272 to M.W.E.), and the Department of Defense Global Emerging Infections Surveillance (GEIS) program (C0366-11-HS to M.W.E.).
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