Community-associated methicillin-resistant Staphylococcus aureus infections in men who have sex with men : A case series

been a significant bacterial pathogen in hospitals and long-term care settings for over four decades (1). Risk factors for colonization and infection with health care-associated MRSA have been well described, and include prolonged hospitalization, dialysis and presence of indwelling catheters (2-5). However, in recent years, several outbreaks of MRSA infection in the United States and Europe have been described in otherwise healthy individuals who lack traditional risk factors for MRSA acquisition. Specifically, outbreaks of community-associated MRSA (CA-MRSA) have occurred in daycare centres, where children come in close physical contact with each other; participants of sports teams; military personnel and men who have sex with men (MSM) (6-10). Although


Study population and study design
A retrospective chart review was performed of all patients with MRSA infection at Maple Leaf Medical Clinic in downtown Toronto between November 2004 and December 2005.The clinic serves a culturally diverse, inner-city population of approximately 12,000 patients, 2500 of whom are infected with HIV.Approximately 95% of HIV-positive patients seen at the clinic are men, the majority of whom are MSM.Patients were identified for MRSA and MRSA-related topics by clinic physicians and by queries in the electronic clinical management system.All patients at the clinic identified as MSM with a clinical manifestation of CA-MRSA and confirmatory microbiological testing were included in the study.

Data collection
Ethics approval was obtained for the publication of the findings.A standard data collection form was created and used for all patients.Charts of eligible patients were reviewed for the extraction of demographic data, risk factors, HIV-related information, initial and follow-up treatment, and clinical course.Demographics included date of birth, sex, ethnicity, MSM status and postal code.The HIV-related information collected included serostatus, CD4 count and viral load results just before CA-MRSA infection, use of trimethoprim-sulfamethoxazole (TMP-SMX) prophylaxis and use of antiretroviral treatment.The clinical characteristics of the infections were extracted including the location, number and size of lesions, the use of incision and drainage, initial and definitive treatments, and whether patients experienced recurrences of infections after they had received treatment.Recurrences were determined by clinical diagnosis and cultures when available.
Laboratory identification and testing of MRSA isolates MRSA was cultured from wound swabs using standard microbiological methods at various Canadian Medical Laboratories.Bio-Rad MRSASelect (Bio-Rad Laboratories, USA) was used as the MRSA screen plates and pink colonies were confirmed as MRSA with a genprobe mecA screen.Antibiograms were collected on all identified strains using BD Phoenix AP (BD Diagnostics, USA) for susceptibilities.Six isolates were retrieved for further testing and were sent to the National Microbiology Laboratory in Winnipeg, Manitoba, for molecular characterization.DNA fingerprinting by pulsed-field gel electrophoresis was performed on these isolates to identify the molecular subtype of MRSA responsible for the outbreak (14).Isolates were also analyzed for the presence of the Panton-Valentine leukocidin (PVL) gene using polymerase chain reaction, and SCCmec typing was determined (15,16).

Statistical analysis
Data for all patients were entered into a Microsoft Access database (Microsoft Corporation, USA).Patient demographics, risk factors, clinical course and microbiological variables were summarized using medians and ranges for continuous variables and proportions for categorical variables.All statistical analyses were performed using SAS version 9.1 statistical software (SAS Institute, USA).

Patient characteristics
Seventeen patients with MRSA infection were identified between November 2004 and December 2005.Patient demographics and individual cases are summarized in Tables 1  and 2, respectively.The median age of subjects was 38 years (range 24 to 50 years).Seventy-six per cent of patients were Caucasian, 5.9% were black and 17.6% were Hispanic.Twelve (71%) of the patients were HIV-positive.Only one patient had   been hospitalized in the previous year, two had undergone surgeries (one unknown and one tympanostomy procedure), and six had received antibiotic treatment in the six months before being diagnosed with CA-MRSA.No patients had an indwelling catheter, received dialysis or were taking prednisone.Social risk factors were more difficult to ascertain from the medical chart.
In the 12 patients who were HIV-positive, the median viral load and CD4+ counts were 9233 copies/mL (range less than 50 copies/mL to 145,565 copies/mL) and 520 cells/mm 3 (range 290 cells/mm 3 to 1084 cells/mm 3 ), respectively.Six patients were taking antiretroviral treatment.No patients were receiving TMP-SMX as prophylaxis for opportunistic infections.

Clinical course and treatment
The most common clinical presentation of CA-MRSA in this cohort was abscess (35.3%), followed by furuncles (17.6%), folliculitis (17.6%), cellulitis (17.6%) and sinusitis (11.8%) (Table 1).The most commonly affected site was the buttocks and genital region (29%), followed by chest and axilla, and face and neck regions.The abscesses ranged in size from 1 cm to 5 cm.None of the patients had signs of systemic illness.Potential risk factors for CA-MRSA infection could not be determined in the majority of cases (Table 2).
Patients presenting with an abscess were treated with incision and drainage, followed by a course of systemic oral antibiotics (n=6).The remaining patients received systemic antibiotic therapy alone.Empirical therapy with beta-lactam antibiotics was initiated in nine patients and was subsequently modified based on the results of the culture and sensitivities.The remaining eight patients received empirical therapy directed against MRSA.Antibacterial regimens included monotherapy with TMP-SMX, and combinations of TMP-SMX and rifampin, TMP-SMX and doxycycline and doxycycline and rifampin (Table 1).The median duration of antibiotic therapy was 10 days (range 10 to 30 days).No patient received therapy with intravenous antibiotics.Commonly used adjuvant therapies included mupirocin to the nares or to the wound site and chlorhexidine washes.Recurrent infections with CA-MRSA were observed in two patients.Both patients initially presented with furuncles and had recurrences within one month of the initial resolution date.The recurrences occurred in the same location as the initial presentation.One recurrence was culture-proven and the other was based on clinical judgment.

Bacterial characteristics
Culture and sensitivity testing demonstrated resistance to all beta-lactam antibiotics and erythromycin; the majority of isolates were resistant to ciprofloxacin (92%) and levofloxacin (77%).In all cases, the cultured isolates were 100% susceptible to TMP-SMX, rifampin, linezolid, gentamicin, clindamycin and nitrofurantoin, while the majority were susceptible to tetracycline (80%).Of the six isolates that were retrieved for further genetic analysis, all were found to carry the SCCmec type IVa gene and the gene that encodes for PVL exotoxin.The six isolates were also identified as the CMRSA-10 (USA300) clone based on fingerprint pattern.

DISCUSSION
CA-MRSA is becoming an increasingly prevalent pathogen, accounting for approximately 8% to 20% of all MRSA isolates in Canada and the United States (17,18).In the present report, we summarize the characteristics of CA-MRSA in a cohort of MSM from a Canadian centre occurring over a 13-month period.All 15 patients who presented with skin and soft tissue infections were amenable to treatment by incision and drainage, and oral antibiotics or oral antibiotics alone.Two patients presented with sinusitis that was treated with antibiotics alone.DNA fingerprinting using pulsed-field gel electrophoresis revealed that the outbreak strain was CMRSA-10, which is equivalent to the USA300 clone responsible for the majority of the community outbreaks in the United States.Genetic testing of six isolates confirmed the presence of genes that encode for the PVL cytotoxin and SCCmecIV cassette.
Our report adds to the existing literature describing the clinical manifestations of CA-MRSA infection in MSM.In a case-control study (19) of 35 HIV-positive MSM with skin infections attributable to CA-MRSA, most patients presented clinically with either an abscess (55.2%) or cellulitis (31.0%).As with our study, infections were associated with the USA300 clone (CMRSA-10) of CA-MRSA.Risk factors for CA-MRSA infection in the aforementioned study were associated with high-risk sex and drug-using behaviours, but not with immune status.In contrast, a separate study of HIV-infected adults with clinically significant health care-associated MRSA infections identified a CD4+ cell count of less than 50 cells/mm 3 , higher plasma viral load and absence of TMP-SMX prophylaxis for opportunistic infections as significant risk factors for MRSA infection (20).In our study, patients with HIV infection did not have advanced disease, as evidenced by the high median CD4+ cell counts before infection.Receipt of an antibiotic within the six months preceding infection was identified as the most common potential risk factor for infection in our cohort.More research is clearly necessary to better ascertain risk factors for CA-MRSA acquisition among this Canadian patient population.
Presently, there are few data describing the optimal treatment of CA-MRSA infections.Recently published guidelines regarding the management and prevention of infections caused by CA-MRSA recommend incision and drainage without antimicrobial therapy in mild cases of skin and soft tissue disease attributable to this organism, with systemic antimicrobial therapy reserved for moderate or severe infections or infections observed in young or immunocompromised hosts (21).Routine decolonization is not recommended as part of the management of CA-MRSA infection, but can be considered in cases of recurrent disease or during the management of outbreaks in selected closed settings (21).

SUMMARY
We describe the clinical characteristics and management of CA-MRSA-related infections in a cohort of MSM.Our findings are limited by the small sample size of our report, and the inability to identify the source of infection or risk factors for infection in the majority of cases.Nevertheless, our experience and that of others reinforces the need to heighten awareness about the emerging role played by CA-MRSA as a pathogenic agent in the outpatient setting.Patient and provider education directed at reinforcing basic hygiene practices and judicious antibiotic use will be essential in curtailing the further spread of CA-MRSA.
Sztramko et al Can J Infect Dis Med Microbiol Vol 18 No 4 July/August 2007 258