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Methicillin-Resistant Staphylococcus aureus as a Common Cause of Vulvar Abscesses

Thurman, Andrea Ries MD1; Satterfield, Tiffany M. DO1; Soper, David E. MD2

doi: 10.1097/AOG.0b013e3181827829
Original Research
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OBJECTIVE: To estimate the incidence of methicillin-resistant Staphylococcus aureus (MRSA) among women with vulvar abscesses and to describe clinical factors associated with inpatient compared with outpatient treatment.

METHODS: We reviewed all women with a vulvar abscess who were treated with incision and drainage between October 2006 to March 2008. We reviewed the abscess cultures and evaluated clinical and laboratory variables associated with inpatient compared with outpatient treatment.

RESULTS: During the 80-week study period, 162 women were treated for a vulvar abscess. Methicillin-resistant S aureus was isolated from 85 of 133 (64%) cultured vulvar abscesses. No presenting signs or symptoms were more common among patients with MRSA abscesses. Women with an MRSA vulvar abscess were not more likely to require inpatient admission or experience treatment complications. Inpatient treatment occurred in 64 of 162 (40%) patients and was predicted by medical comorbidities: diabetes (45.3%, odds ratio [OR] 2.29, 95% confidence interval [CI] 1.12–4.72), hypertension (34.4%, OR 2.33, 95% CI 1.06–5.13), initial serum glucose greater than 200 (37.5%, OR 3.32, 95% CI 1.48–7.51), and signs of worse infection, ie, larger abscesses (mean 5.2 cm) (P<.001) and elevated white blood cell count of at least 12,000/mm3 (45.3%, OR 3.04, 95% CI 1.44–6.43).

CONCLUSION: Methicillin-resistant S aureus was the most common organism isolated from vulvar abscesses. Inpatient treatment is more common in women with medical comorbidities, larger abscesses, and signs of systemic illness. An antibiotic regimen with activity against MRSA, such as trimethoprim-sulfamethoxazole, should be considered in similar populations with vulvar abscesses.

LEVEL OF EVIDENCE: III

Methicillin-resistant Staphylococcus aureus is the most common microorganism isolated from vulvar abscesses.

From the Departments of Obstetrics and Gynecology, 1University of Texas Health Sciences Center San Antonio, Texas; and 2Medical University of South Carolina, Charleston, South Carolina.

See related article on page 533.

Corresponding author: Andrea Ries Thurman, MD, Assistant Professor, Obstetrics and Gynecology, University of Texas Health Science Center San Antonio, 7703 Floyd Curl Drive, Mail Code 7836, San Antonio, TX 78229-3900; e-mail: thurmana@uthscsa.edu.

Financial Disclosure The authors have no potential conflicts of interest to disclose.

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a common cause of community- acquired skin and soft-tissue infections among emergency room patients, athletes, military trainees, children, intravenous drug users, public housing residents, prisoners, and men who have sex with men.1–9 Unlike hospital-acquired MRSA, patients with community-acquired MRSA do not have the typical risk factors of prolonged broad-spectrum antibiotic use, recent surgery, dialysis, indwelling catheters, or admission to intensive care units (ICUs) or long-term care facilities.1,2,4,7 Unlike hospital-acquired MRSA, most community-acquired MRSA species have a leukocyte-destroying exotoxin, produced by the Panton-Valentine leukocidin locus, which causes tissue necrosis.8 This virulence factor leads to infection in nonimmunosuppressed, noncompromised healthy women. However, community-acquired MRSA typically has less resistance to other non–β-lactam antibiotics as compared with hospital-acquired MRSA.1,2,4

Reports from obstetric populations have shown an emergence of community-acquired MRSA colonization of the perineum, rectum, and lower genital tract.10–12 However, data are limited on vulvar abscesses in general, and specifically on the incidence of MRSA in these gynecologic infections. The vulva is an area susceptible to infection with community-acquired MRSA due to risk factors such as shaving, waxing, and sharing of personal hygiene products such as soaps and razors.4,13,14 There are also case reports of heterosexual transmission of community-acquired MRSA genital infection.15 Obesity is known to increase the risk of skin and soft-tissue infections, possibly due to altered epidermal, lymphatic, or microvascular function.16 The vulva may be an area that is more difficult to clean in obese or disabled women, and poor hygiene is also associated with MRSA infection.1,2,4–6,13

The objective of this study was to estimate the incidence of MRSA in a large cohort of women with vulvar abscesses who were treated with either inpatient or outpatient surgical incision and drainage. A secondary analysis was done to identify clinical factors associated with MRSA compared with non-MRSA vulvar abscesses and inpatient compared with outpatient treatment.

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MATERIALS AND METHODS

This study was approved by the Institutional Review Board at the University of Texas Health Sciences Center San Antonio, a large county hospital serving primarily low-income Hispanic patients. We obtained a listing of all women treated as inpatients or outpatients for the following Current Procedural Terminology codes: 616.3 (abscess of Bartholin’s Gland), 616.4 (other abscess of vulva), 616.5 (ulceration of the vulva unspecified), and 616.8 (other specified inflammatory disease of the vulva) at University of Texas Health Sciences Center San Antonio from October 2006 until March 2008. This time period was chosen because it marked the onset of the electronic medical record to the present. Each chart was deidentified and abstracted for patient age, ethnicity (Hispanic, non-Hispanic white, non-Hispanic African American, and other), body mass index, insurance status (none, public, commercial/private insurance), pregnancy status (pregnant or not pregnant), tobacco use, diabetes mellitus (DM), hypertension, presence or absence of genital hair shaving, largest size of the abscess in centimeters, history of a vulvar abscess, initial serum glucose, intake white blood cell count, and body temperature (less than 38°C or 38°C or more), organism cultured, presence of a sexually transmitted infection, inpatient or outpatient treatment, length of inpatient hospital stay, use of antimicrobial therapy, and the occurrence of any short-term complications (readmission within 30 days, treatment failure [reoperation within 30 days], intensive care unit admission, sepsis, diabetic ketoacidosis, or death). Patients were not contacted for additional clinical information.

The primary outcome was the microorganism cultured from the vulvar abscess. Secondary outcome variables were presenting signs, symptoms, and epidemiologic variables associated with MRSA compared with non-MRSA vulvar abscesses and inpatient compared with outpatient treatment.

Aerobic and anaerobic cultures were obtained from the abscess with sterile Dacron (E.I. du Pont de Nemours and Company, Wilmington, DE) swabs and placed in Amies without charcoal transport media. Each Dacron swab was streaked onto Blood, Colistan Naladix Acid, Chromogenic, MacConkey, Bile-Esculin/ Lake Blood, and anaerobic blood with phenylethyl alcohol agars and placed in an enriched thioglycollate broth and incubated for 24–48 hours. Anaerobic plates were incubated in an anaerobic hood for 5 days and checked daily. Antimicrobial resistance was determined by automated broth microdilution. Isolates were considered resistant to methicillin if the oxacillin minimum inhibitory concentration was at least 4 micrograms/mL. Methicillin-resistant S aureus isolates were also tested for susceptibility to vancomycin, erythromycin, clindamycin, trimethoprim-sulfamethoxazole, and doxycycline. Susceptibility testing to other agents such as rifampin or newer agents such as linezolid was not done.

Descriptive statistics were used to summarize the characteristics of the patients and the prevalence of MRSA. Univariable analysis was done with the χ2 statistic for categorical variables and the Student t test for continuous variables. Variables that were statistically significant (P<.05) in the univariable analyses were further explored using multivariable forward stepwise logistic regression analysis. Epi Info (Centers for Disease Control and Prevention, Atlanta, GA) and SPSS (SPSS Inc., Chicago, IL) software were used for analysis.

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RESULTS

A total of 234 women were identified from the Current Procedural Terminology list. Figure 1 details patients in the analysis. We excluded 72 patients with vulvar lesions other than a vulvar abscess. Therefore, 162 women with a vulvar abscess were included in this cohort. None of the women were currently or recently (within 30 days) hospitalized. The data were obtained over an 80-week period, averaging two women presenting weekly for surgical treatment of a vulvar abscess.

Fig

Fig

Vulvar abscess cultures were obtained in 133 of 162 (82%) patients. Methicillin-resistant S aureus was isolated from 85 vulvar abscesses (85 of 133; 64%) and other non-MRSA organisms, mainly labeled as “usual genital flora,” group B streptococci, Enterococcus species, Proteus mirabilis, or Escherichia coli, were isolated from 48 of 133 (36%) vulvar abscesses. All of the P mirabilis and E coli isolates were sensitive to trimethoprim-sulfamethoxazole, as were 90% of the group B streptococci isolates. Antibiotic susceptibility to Enterococcus was only tested for ampicillin and vancomycin, and all isolates were sensitive to both. The MRSA isolates were sensitive to clindamycin (72%), trimethoprim-sulfamethoxazole (96%), and doxycycline (96%).

Table 1 compares the clinical characteristics of patients with an MRSA vulvar abscess (n=85) compared with patients with a vulvar abscess containing non-MRSA bacteria (n=48). Women with non-MRSA vulvar abscesses were more likely to report hypertension and tobacco use. No presenting sign, symptom, or epidemiologic variable was found to be significantly predictive of an MRSA vulvar abscess. Methicillin-resistant S aureus infection was not associated with inpatient treatment or the occurrence of any short-term complications.

Table 1

Table 1

Table 2 compares women who received inpatient (n=64) with outpatient (n=98) treatment. All outpatients had incision and drainage of the vulvar abscess in the emergency department procedure room, using a local anesthetic. Most inpatients had incision and drainage of the vulvar abscess in the operating room under general anesthesia; two had incision and drainage of the vulvar abscess in the outpatient procedure room with inpatient admission to manage signs of infection or medical comorbidities. Most (90.6%) of the inpatients also received intravenous antibiotic therapy. The average length of stay for an inpatient was 3.8 days; the median length of inpatient stay was 2 days and the range was 1–39 days. Using the variables that were significant in the univariable analysis of inpatient compared with outpatient treatment (DM, hypertension, initial white blood cell count more than 12,000/mm3, initial serum glucose more than 200 mg/dL, largest abscess dimension of 5 cm or more), we performed a forward, step-wise multivariable logistic regression analysis. We chose the initial blood glucose of 200 mg/dL or more, because the American Diabetes Association considers a random blood glucose of 200 mg/dL or more to be diagnostic of diabetes. Inpatient admission was independently associated with an abscess of 5 cm or more (adjusted odds ratio 5.81, 95% confidence interval 3.30–6.42) and an initial blood glucose of 200 mg/dL or more (adjusted odds ratio 1.95 95% confidence interval 1.25–3.04).

Table 2

Table 2

Screening for sexually transmitted infections was done infrequently: 31 of 85 patients with MRSA and 24 of 48 patients with other bacteria. Patients with an MRSA vulvar abscess were not more likely to be diagnosed with a sexually transmitted infection (two of 31) as compared with patients with a non-MRSA vulvar abscess (three of 24) (P=.44), but these data are limited by small sample size. Sexually transmitted infection screening was done in 34 of 98 outpatients, and few were found to have a sexually transmitted infection: two were diagnosed with Chlamydia trachomatis cervicitis, and one patient was known to have human immunodeficiency virus (HIV). Sexually transmitted infection screening was done in 34 of 64 of inpatients: two were found to have Trichomonas vaginalis, and one was diagnosed with C trachomatis cervicitis.

The presence or absence of pubic hair shaving was also documented infrequently: only 19 of 85 patients with MRSA and eight of 48 patients with non-MRSA abscesses had documentation of this variable (six of 85 MRSA compared with three of 48 non-MRSA women had recently shaved, P=.85). Among inpatients, 20 of 64 had documentation of pubic hair shaving (four had recently shaved), and among outpatients, only 14 of 98 had documentation of this variable (nine had genital hair shaving) (four of 64 compared with nine of 98, P=.50), but comparison is limited due to small cell size.

Most inpatients and outpatients were discharged home with a prescription for oral antibiotics, clindamycin (81%), trimethoprim-sulfamethoxazole (14%), doxycycline (4%), and there was no difference in discharge antibiotic regimens between women treated as outpatients compared with inpatients (data not shown). Two of the patients were currently incarcerated, and both had MRSA. Twelve patients experienced treatment complications, 10 of which were a recurrence of a vulvar abscess within 30 days. Of the 10 patients with a recurrent abscess, four patients required a repeat admission with incision and drainage in the operating room. One patient, whose vulvar abscess grew “usual genital flora” died during an extended ICU admission, after several wound débridements, prolonged intubation, and complications of DM. Another patient was admitted to the ICU for sepsis and diabetic ketoacidosis, and her vulvar abscess, which was MRSA sensitive to vancomycin, clindamycin, and trimethoprim-sulfamethoxazole, required several extensive surgical débridements.

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DISCUSSION

Methicillin-resistant S aureus was the most common organism isolated from vulvar abscesses in this large cohort. Our findings are consistent with several reports of the high prevalence of MRSA in skin and soft-tissue infections, but we extend the literature to describe MRSA in vulvar abscesses, which are morbid gynecologic infections.1,2,4,7–9,17,18 The incidence of MRSA in this study is consistent with other large studies of skin and soft-tissue infections, 15–74%, varying by geographic location and medical center.4,7 We performed a literature search, using several combinations of the keywords vulva, labia, genital, gynecologic AND abscess, infection, diabetes, necrotizing fasciitis; this report likely represents the largest cohort of vulvar abscesses described in recent literature.

Methicillin-resistant S aureus skin and soft-tissue infections are often confused with spider bites, and South Texas is a region that harbors brown recluse spiders, known for necrotic lesions.2,4,19 Several of our patients reported a “spider bite” as their chief complaint, but this variable was not documented uniformly. We found that initial signs and symptoms could not differentiate an MRSA from a non-MRSA vulvar abscess, consistent with other studies of MRSA skin and soft-tissue infections.3,20 Thus, the gynecologist evaluating a woman with a vulvar abscess should consider MRSA as a cause.3 Our data suggest that if an oral antibiotic is prescribed, trimethoprim-sulfamethoxazole should be the first line of treatment, because this medication covered almost all of the MRSA and non-MRSA species recovered from vulvar abscesses. Trimethoprim-sulfamethoxazole is also significantly less expensive than clindamycin. With the increasing prevalence of MRSA, we, along with many experts, recommend that β-lactam antibiotics can no longer be considered for empirical therapy of community-acquired skin and soft-tissue infections.1,2

Our study demonstrates that vulvar abscesses are a morbid condition, with 40% of women requiring inpatient treatment for an average of 3 days. Previous reports of MRSA skin and soft-tissue infections among emergency room patients and pregnant and postpartum women found that 23–63% of patients were hospitalized for treatment.11,18 Our data are in agreement with a previous study that found that inpatients hospitalized for MRSA skin and soft-tissue infections had similar outcomes as compared with patients hospitalized for non-MRSA skin and soft-tissue infections.20 Similar to other authors, we found that the clinician may use traditional measures of disease severity when selecting outpatient or inpatient therapy.21

All of our patients underwent surgical incision and drainage. The management of uncomplicated community-acquired MRSA abscesses is primarily incision and drainage, and it is debated whether antibiotic therapy adds additional benefit, especially in patients without surrounding cellulitis.2,7,17,20,22

Most of our inpatients received intravenous vancomycin or clindamycin until signs of cellulitis resolved or until they were afebrile for 48 hours. Most women were sent home with additional antibiotic coverage. The susceptibility profile of the MRSA cultured in this study is similar to other reports.1–3 We have changed our treatment algorithm based on these data, and use trimethoprim-sulfamethoxazole as first-line therapy when oral antibiotics are used after surgical incision and drainage.

The prevalence of perirectal/genital colonization of MRSA among pregnant women (0.5–3.5%) is comparable to the incidence of MRSA nasal colonization (3%) among a large cohort of healthy military recruits.8,10–12 A limitation of our study is that we do not know our population’s baseline prevalence of vulvar MRSA colonization. Although many of our patients reported a history of vulvar abscesses, we did not attempt to decolonize any patient, because the efficacy of this process for preventing recurrent MRSA infections is unclear.1,2 We did not track recent antibiotic use, a risk factor for MRSA infection (4, 7–9). However, many antibiotics are available to our patients over the counter in Mexico. We did not perform pulsed-field gel electrophoresis typing on the MRSA isolate, because most community-acquired MRSA isolates are USA300 pulse field type.4 We plan to prospectively investigate patients with a vulvar abscess and evaluate additional risk factors: recent (less than 30 days) incarceration, sexual contact with a partner who has genital abscesses/lesions, the presence of cellulitis, chief complaints of a “spider-bite,” previous MRSA diagnoses, and recent antibiotic use, specifically antibiotics obtained over the counter in Mexico. We also plan to follow patients after treatment to determine long-term complications and recurrence rates. Of note, two of our patients had wound vacuums placed after debridement of large vulvar abscesses, a process that is not widely reported.

In conclusion, recent literature confirms an increase in the prevalence of community-acquired MRSA skin and soft-tissue infections. Methicillin-resistant S aureus was the most common organism isolated in this large series of women with vulvar abscesses. Although community-acquired MRSA is a virulent organism, most of the MRSA isolated in this series were sensitive to trimethoprim-sulfamethoxazole. The vulva may be an area that is particularly susceptible to an MRSA skin and soft-tissue infection. We found no presenting signs or symptoms that were predictive of MRSA as compared with other genital flora. The gynecologist evaluating a patient with a vulvar abscess should consider MRSA as an cause. An antibiotic regimen with activity against MRSA, such as trimethoprim-sulfamethoxazole, should be initiated in similar populations with vulvar abscesses.

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© 2008 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.