MRSA a Dominant Pathogen in Perineal Abscesses

SEATTLE — Methicillin-resistant Staphylococcus aureus is found in one-third of cases of perineal and buttock abscesses in women, and it accounts for fully half of the monomicrobial abscesses, according to one hospital's experience.

“MRSA is a common problem in our hospitals and in our community, and it certainly commands our attention,” study author Dr. Susan M. Lareau said at the annual meeting of the Infectious Diseases Society for Obstetrics and Gynecology. She noted that a previous report found that MRSA was the leading cause of skin and soft-tissue infection in most emergency departments but did not address the proportion of perineal infections caused by this pathogen (N. Engl. J. Med. 2006;355:666-74).

Dr. Lareau of the Magee-Womens Hospital in Pittsburgh used diagnostic codes to identify retrospectively all cases of perineal and buttock abscesses seen at the hospital between 2003 and 2007 and then reviewed their characteristics. She included cases involving the vulva, Bartholin glands, and buttocks, and excluded cases involving the perianal and rectal areas.

The process identified 126 patients, Dr. Lareau reported. This group consisted of 64 patients (51%) with vulvar abscesses, 41 patients (33%) with Bartholin gland abscesses, 19 patients (15%) with buttock abscesses, and 2 patients (2%) with combined buttock and vulvar abscesses.

Cultures had been obtained in 72 of the patients and were positive for MRSA in 33%. By site, MRSA was found in 64% of buttock abscesses, 50% of combined buttock and vulvar abscesses, 33% of vulvar abscesses, and 7% of Bartholin gland abscesses.

“It's generally been thought that vulvar abscesses are polymicrobial, and that has driven our treatment, when necessary,” Dr. Lareau said. However, most (69%) of the 72 cases were monomicrobial. MRSA accounted for fully 50% of these infections; the next most common pathogens were group B streptococcus and methicillin-susceptible S. aureus, each of which accounted for only 14% of these infections.

Age, race, body mass index, pregnancy, and several comorbidities (diabetes, cancer, and coronary artery disease) did not significantly predict MRSA infection, but site did, according to Dr. Lareau. Relative to patients with Bartholin gland abscesses, patients with buttock abscesses were significantly more likely to be positive for MRSA (odds ratio 28), and patients with vulvar infections were nonsignificantly more likely to be MRSA positive (OR 7). However, Dr. Lareau said, confidence intervals were wide, probably because of the small sample size.

“We wanted to look at the outcomes associated with MRSA to see if this was a more virulent and more difficult to treat infection,” Dr. Lareau explained. In fact, the data did not support such associations, showing that MRSA-positive and MRSA-negative patients had identical median lengths of hospital stay (2 days) and did not differ significantly with respect to the rate of abscess drainage in the operating room (29% vs. 71%).

An analysis of trends over the 5-year study period showed that the total number of cases of perineal abscess seen at the hospital increased from about 20 to 55 per year. At the same time, the number of cases of MRSA perineal abscess, although still modest, increased at a much faster pace, from 1 to 12 per year.

“MRSA is the dominant pathogen in perineal infections at Magee-Womens Hospital,” Dr. Lareau concluded, adding that the study was unable to find clear demographic predictors of which patients are most likely to have this infection. “I would advocate considering empiric coverage for MRSA when you have a vulvar abscess that requires treatment,” she recommended.

Dr. Lareau reported that she had no conflicts of interest in association with the study.

The number of cases of MRSA perineal abscess increased from 1 to 12 per year. DR. LAREAU

SEATTLE — Methicillin-resistant Staphylococcus aureus is found in one-third of cases of perineal and buttock abscesses in women, and it accounts for fully half of the monomicrobial abscesses, according to one hospital's experience.

“MRSA is a common problem in our hospitals and in our community, and it certainly commands our attention,” study author Dr. Susan M. Lareau said at the annual meeting of the Infectious Diseases Society for Obstetrics and Gynecology. She noted that a previous report found that MRSA was the leading cause of skin and soft-tissue infection in most emergency departments but did not address the proportion of perineal infections caused by this pathogen (N. Engl. J. Med. 2006;355:666-74).

Dr. Lareau of the Magee-Womens Hospital in Pittsburgh used diagnostic codes to identify retrospectively all cases of perineal and buttock abscesses seen at the hospital between 2003 and 2007 and then reviewed their characteristics. She included cases involving the vulva, Bartholin glands, and buttocks, and excluded cases involving the perianal and rectal areas.

The process identified 126 patients, Dr. Lareau reported. This group consisted of 64 patients (51%) with vulvar abscesses, 41 patients (33%) with Bartholin gland abscesses, 19 patients (15%) with buttock abscesses, and 2 patients (2%) with combined buttock and vulvar abscesses.

Cultures had been obtained in 72 of the patients and were positive for MRSA in 33%. By site, MRSA was found in 64% of buttock abscesses, 50% of combined buttock and vulvar abscesses, 33% of vulvar abscesses, and 7% of Bartholin gland abscesses.

“It's generally been thought that vulvar abscesses are polymicrobial, and that has driven our treatment, when necessary,” Dr. Lareau said. However, most (69%) of the 72 cases were monomicrobial. MRSA accounted for fully 50% of these infections; the next most common pathogens were group B streptococcus and methicillin-susceptible S. aureus, each of which accounted for only 14% of these infections.

Age, race, body mass index, pregnancy, and several comorbidities (diabetes, cancer, and coronary artery disease) did not significantly predict MRSA infection, but site did, according to Dr. Lareau. Relative to patients with Bartholin gland abscesses, patients with buttock abscesses were significantly more likely to be positive for MRSA (odds ratio 28), and patients with vulvar infections were nonsignificantly more likely to be MRSA positive (OR 7). However, Dr. Lareau said, confidence intervals were wide, probably because of the small sample size.

“We wanted to look at the outcomes associated with MRSA to see if this was a more virulent and more difficult to treat infection,” Dr. Lareau explained. In fact, the data did not support such associations, showing that MRSA-positive and MRSA-negative patients had identical median lengths of hospital stay (2 days) and did not differ significantly with respect to the rate of abscess drainage in the operating room (29% vs. 71%).

An analysis of trends over the 5-year study period showed that the total number of cases of perineal abscess seen at the hospital increased from about 20 to 55 per year. At the same time, the number of cases of MRSA perineal abscess, although still modest, increased at a much faster pace, from 1 to 12 per year.

“MRSA is the dominant pathogen in perineal infections at Magee-Womens Hospital,” Dr. Lareau concluded, adding that the study was unable to find clear demographic predictors of which patients are most likely to have this infection. “I would advocate considering empiric coverage for MRSA when you have a vulvar abscess that requires treatment,” she recommended.

Dr. Lareau reported that she had no conflicts of interest in association with the study.

The number of cases of MRSA perineal abscess increased from 1 to 12 per year. DR. LAREAU

SEATTLE — Methicillin-resistant Staphylococcus aureus is found in one-third of cases of perineal and buttock abscesses in women, and it accounts for fully half of the monomicrobial abscesses, according to one hospital's experience.

“MRSA is a common problem in our hospitals and in our community, and it certainly commands our attention,” study author Dr. Susan M. Lareau said at the annual meeting of the Infectious Diseases Society for Obstetrics and Gynecology. She noted that a previous report found that MRSA was the leading cause of skin and soft-tissue infection in most emergency departments but did not address the proportion of perineal infections caused by this pathogen (N. Engl. J. Med. 2006;355:666-74).

Dr. Lareau of the Magee-Womens Hospital in Pittsburgh used diagnostic codes to identify retrospectively all cases of perineal and buttock abscesses seen at the hospital between 2003 and 2007 and then reviewed their characteristics. She included cases involving the vulva, Bartholin glands, and buttocks, and excluded cases involving the perianal and rectal areas.

The process identified 126 patients, Dr. Lareau reported. This group consisted of 64 patients (51%) with vulvar abscesses, 41 patients (33%) with Bartholin gland abscesses, 19 patients (15%) with buttock abscesses, and 2 patients (2%) with combined buttock and vulvar abscesses.

Cultures had been obtained in 72 of the patients and were positive for MRSA in 33%. By site, MRSA was found in 64% of buttock abscesses, 50% of combined buttock and vulvar abscesses, 33% of vulvar abscesses, and 7% of Bartholin gland abscesses.

“It's generally been thought that vulvar abscesses are polymicrobial, and that has driven our treatment, when necessary,” Dr. Lareau said. However, most (69%) of the 72 cases were monomicrobial. MRSA accounted for fully 50% of these infections; the next most common pathogens were group B streptococcus and methicillin-susceptible S. aureus, each of which accounted for only 14% of these infections.

Age, race, body mass index, pregnancy, and several comorbidities (diabetes, cancer, and coronary artery disease) did not significantly predict MRSA infection, but site did, according to Dr. Lareau. Relative to patients with Bartholin gland abscesses, patients with buttock abscesses were significantly more likely to be positive for MRSA (odds ratio 28), and patients with vulvar infections were nonsignificantly more likely to be MRSA positive (OR 7). However, Dr. Lareau said, confidence intervals were wide, probably because of the small sample size.

“We wanted to look at the outcomes associated with MRSA to see if this was a more virulent and more difficult to treat infection,” Dr. Lareau explained. In fact, the data did not support such associations, showing that MRSA-positive and MRSA-negative patients had identical median lengths of hospital stay (2 days) and did not differ significantly with respect to the rate of abscess drainage in the operating room (29% vs. 71%).

An analysis of trends over the 5-year study period showed that the total number of cases of perineal abscess seen at the hospital increased from about 20 to 55 per year. At the same time, the number of cases of MRSA perineal abscess, although still modest, increased at a much faster pace, from 1 to 12 per year.

“MRSA is the dominant pathogen in perineal infections at Magee-Womens Hospital,” Dr. Lareau concluded, adding that the study was unable to find clear demographic predictors of which patients are most likely to have this infection. “I would advocate considering empiric coverage for MRSA when you have a vulvar abscess that requires treatment,” she recommended.

Dr. Lareau reported that she had no conflicts of interest in association with the study.

The number of cases of MRSA perineal abscess increased from 1 to 12 per year. DR. LAREAU