Breast infection in lactating women can present with a wide spectrum of clinical findings, including cellulitis and breast abscess. The reported incidence of inflammatory processes during lactation is between 2% and 10%.1–3 Abscess formation can result from inadequate treatment and has been reported to occur among 4.6% to11% of women with mastitis.4,5
The emergence of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) in the obstetrical population has been described, with a reported 10-fold increase in soft tissue and skin infections between the years 2000 and 2004.6,7 Reported prevalence rates of MRSA in pregnant women range from 0.5% to 3%, with both genital and nasal cultures.8–10 With reports of outbreaks among family members, day care facilities, and newborn nurseries, it is reasonable to consider the pregnant and postpartum woman at risk for infection.11–13
New concerns for puerperal mastitis associated with community-acquired MRSA have prompted several investigations into causative agents and risk factors. Of puerperal infections caused by community-acquired MRSA, up to 50% were associated with either mastitis or breast abscess.6,7 In a recent study of culture-confirmed staphylococcus-associated postpartum mastitis, greater than 95% of breast-milk or abscess MRSA isolates were genotypically proven community-acquired MRSA.14 Our objective was to estimate the incidence of puerperal mastitis requiring hospital admission and to describe associated demographic and obstetric risk factors for this condition. In addition, we sought to describe trends in bacteriology among isolates obtained from both breast abscess and breast-milk aspirates, with a focus on treatment strategies used for community-acquired MRSA.
MATERIALS AND METHODS
Institutional review board approval from the University of Texas Southwestern Medical Center in Dallas was obtained. All patients admitted to Parkland Memorial Hospital with the diagnosis of puerperal mastitis between January 1997 and December 2005 were identified by International Classification of Diseases, 9th Revision, codes (675.1, 675.2). Medical records were reviewed, and data collected included demographic characteristics, clinical presentation, bacteriology, treatment, duration of admission, and premorbid antibiotic exposure. Criteria for admission included fever higher than 38.0°C and clinically significant breast cellulitis concerning for septicemia or abscess. During the study period, women admitted with uncomplicated mastitis were treated with intravenous antibiotics and instructed to empty the breast by frequent nursing or manual emptying. Women with breast abscesses were treated with surgical drainage and antibiotic therapy as needed. A breast culture or milk aspirate was collected before initiation of antibiotics. Community-acquired MRSA isolates were characterized by susceptibility testing and were defined as S. aureus resistant to methicillin, erythromycin, and β-lactam agents.7,15 This was confirmed by examining antibiograms specific for Parkland Hospital during the same time period. Demography and obstetric outcomes were compared with all other pregnant women delivered at our hospital within the same time span. These selected demographic and obstetric outcomes were obtained from a previously described, continuously updated, obstetric computerized database.16 Student’s t, Wilcoxon rank sum, Kruskal-Wallis, Mantel-Haenszel χ2, and Pearson χ2 tests were employed for data evaluation, with a P value less than .05 considered significant.
One hundred twenty-seven of 136,459 women delivered at our teaching hospital during the study period were admitted for postpartum mastitis (9.3 [95% confidence interval (CI) 7.8–11.1] per 10,000 deliveries). The incidence of mastitis only was 6.7 (95% CI 5.4–8.3) per 10,000 deliveries, and the incidence of mastitis with breast abscess was 2.6 (95% CI 1.8–3.6) per 10,000 deliveries.
The majority (85%) of the women were Hispanic, and 55 (43%) were primiparous. Most underwent vaginal delivery (78%), and 23 (18%) required intrapartum antibiotics during labor and delivery admission. Eighty-two percent reported breast-feeding either exclusively or in addition to a breast pump. The most common clinical findings were tenderness and erythema (89%). Of the 127 women admitted, 35 were suspected of having a breast abscess. Of these, 29 (83%) required incision and drainage. The median interval from delivery date to date of admission for uncomplicated mastitis and mastitis with abscess was 14 (95% CI 11–21) and 24 (95% CI 17–31) days, respectively. P=.001. The median length of admission was 3 days (95% CI 2–3) for the mastitis-only group and 3 days (95% CI 2–5) for the abscess group (P=.23). Culture results were available for 81 (64%) of the 127 women admitted; 54 (59%) for the mastitis-only group and 27 (77%) for the abscess group (P=.05).
Demographic variables and obstetric outcomes between women with mastitis and the general obstetrical population at Parkland Hospital then were compared (Table 1). During the study period, 136,459 women delivered in the same labor and delivery unit where the patients with mastitis were admitted. Puerperal mastitis was associated with younger women (P<.001) and decreased parity (P=.02). Previous cesarean delivery, intrapartum antibiotic exposure, and frequency of hypertensive disorders or diabetes did not differ between the two groups. All available culture results were analyzed for antibiotic-resistance patterns.
There were 54 culture results available for the 92 women with mastitis not associated with a breast abscess. In this group, methicillin-sensitive S. aureus was the most common organism isolated from breast-milk aspirates (44%), followed by Staphylococcus epidermidis (35%) (see Box). Culture results were available for 27 of 35 women with puerperal mastitis complicated by breast abscess. Clinically significant breast abscess (n=35, 28%) was seen most commonly with community-acquired MRSA (n=18, 67%) during the data-collection period, followed by methicillin-sensitive S. aureus (19%). Two of the cultures positive for community-acquired MRSA had concomitant growth of a second organism, S. epidermidis in one and Enterobacter cloacae in another. No growth was reported in two samples (7%).
Community-acquired MRSA was found to be prevalent in patients with breast abscesses throughout the duration of the reported cohort. The ratio of community-acquired MRSA to methicillin-sensitive S. aureus did not change during the study period.
In the nonabscess group, 44 of 92 (48%) women received intravenous nafcillin for 24 hours followed by oral dicloxacillin. Eighteen (20%) received oral dicloxacillin alone. Twelve (13%) received intravenous gentamicin and clindamycin in combination, and 10 (11%) received intravenous cefazolin followed by oral cephalexin. Other antimicrobial agents used in these patients included intravenous ampicillin (3%) and doxycycline (1%).
The majority of women in the abscess group (18 women, 51%) received intravenous cefazolin for 24 hours followed by oral cephalexin for presumed methicillin-sensitive S. aureus. Eleven (31%) received intravenous clindamycin, four (11%) as monotherapy and 20% in conjunction with other intravenous antibiotics: four (11%) with cephalexin, two (6%) with vancomycin, and one (3%) with gentamicin. Two women (6%) were started on intravenous gentamicin, and four (11%) were treated with intravenous fluoroquinolone during their hospital admission. One patient with a recurrent history of culture-proven MRSA lesions was treated with intravenous vancomycin as monotherapy. Although the other two patients demonstrated clinical improvement with incision, drainage, and antimicrobial regimens specific for methicillin-sensitive S. aureus, they were initiated on intravenous vancomycin after culture results were determined to be MRSA. The remaining 15 (56%) women with culture-proven MRSA did not receive antibiotic therapy to which this organism was sensitive. They were discharged without complication, and there were no treatment failures.
There was no statistically significant difference in duration of hospital stay between women with community-acquired MRSA directed therapy and nondirected therapy, between women with culture proven community-acquired MRSA and those with other bacterial culture results, or in women for whom culture results were unavailable (P=.07) There were no significant differences in demographic and obstetric variables between the community-acquired MRSA group and other study patients (P=.09).
In our case series, 127 of 136,459 women delivered at our teaching hospital were admitted for puerperal mastitis (9.3 [95% CI 7.8–11.1] per 10,000 deliveries). The incidence of mastitis only during the study period was 6.7 (95% CI 5.4–8.3) per 10,000 deliveries, and the incidence of mastitis with breast abscess was 2.6 (95% CI 1.8–3.6) per 10,000 deliveries. Puerperal mastitis was not significantly associated with any demographic or obstetrical variable except young age and decreased parity. Infection associated with community-acquired MRSA was most commonly associated with breast abscess.
Community-acquired MRSA has become a worldwide concern, with reported prevalence rates between 0.2% and 6.1% in the United States depending on the definition used for classification.17 Community-acquired MRSA has been linked to a spectrum of diseases mostly related to skin and soft tissue infections and is more common in young patients without identifiable risk factors.17 However, more severe manifestations have been reported, including sepsis and necrotizing pneumonia. In a recent study, MRSA was isolated in greater than 59% of patients presenting to the emergency department for skin abscesses. Of these, 97% were typed as community-acquired strains.18 As these infections have spread through the community, increasing rates of community-acquired MRSA have been found among women and children, either as asymptomatic carriers or with significant infectious morbidity.6,7,19,20 Often, clinical presentations of community-acquired MRSA in the obstetrical setting have presented as puerperal mastitis with breast abscess in women with an uncomplicated pregnancy and labor and delivery course.7,14 According to a recent study, cases of spontaneous postpartum mastitis associated with community-acquired MRSA have increased ninefold in the past 5 years.14
We discovered that the most important component of treatment for the cohort consisted of draining the infected breast, either by manual emptying, breast-feeding, or, in cases with abscess, incision and drainage. There have been several studies reflecting the importance of frequent drainage for the treatment of mastitis. In one study evaluating mastitis without abscess, frequent emptying without antibiotics was curative for mastitis related to coagulase-negative staphylococcus. In another study, frequent emptying reduced the duration of clinical symptoms by more than 50% compared with women who received antibiotic alone.21,22 Of the 18 abscess patients with culture-proven community-acquired MRSA puerperal mastitis, only three patients received antibiotic coverage directed against this organism. However, all patients demonstrated complete resolution of clinical infection before culture results were known, with the exception of one woman admitted for a known community-acquired MRSA-positive recurrent abscess who was started on vancomycin on initial presentation. Similar findings have been reported in pediatric and other adult studies where antibiotic therapy directed at community-acquired MRSA for soft tissue infections was unnecessary as long as adequate drainage was performed early.23,24 It is important to obtain cultures when managing acute mastitis or breast abscess so that trends in antibiotic sensitivities of infecting organisms can be monitored over time at individual hospitals. Although this may help direct empiric therapy, the clinician may be reassured that the use of empiric antibiotics not directed at community-acquired MRSA did not adversely affect the outcome in our patient population.
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