Since the first isolation of MRSA by Jevons in 1961 [6], the infection and isolation rates of MRSA have been increasing worldwide, and it has become one of the primary pathogens of nosocomial and community-acquired infections [8, 9]. Annually, the number of deaths caused by MRSA infection in the United States is equivalent to the deaths caused by AIDS, tuberculosis and viral hepatitis combined [10]. The prevalence of MRSA infection has become a serious clinical and public health problem.
In recent years, the detection rate of MRSA in the breast milk and pus of lactating patients has gradually increased [2, 3]. Stafford I and Moazzez A et al. [2, 3] found that the detection rate of MRSA in patients with breast abscesses and mastitis was 67% and 58%, respectively. In our study, of the 1481 patients from whom a bacterial culture of pus was collected, 260 cases of MRSA were detected, with a detection rate of 17.56%, making our detection rate lower than that of Stafford I and Moazzez A et al. The sample sizes in the studies of Stafford I and Moazzez A et al. were small, at 35 and 44, respectively, which are far smaller than our sample size. This difference could explain our lower detection rate than that of these two studies. Although the MRSA infection rate in lactating patients is increasing, the infection cause remains unclear. Some scholars speculated that patients need hospitalization before and after delivery, which could increase the probability of MRSA infection, but further research is required to confirm this [11–14].
In our study, whether the patients were hospitalized was used as an indicator for evaluating the patients’ condition to compare the severity in the two groups. Evaluating the postpartum time (puerperium), patients’ age, location of abscess cavities, number of abscess cavities and amount of pus, the clinical manifestations of the patients infected with the two bacteria were compared. Furthermore, the therapeutic effect of the frequency of needle aspiration, needle aspiration efficacy, treatment duration and antibiotic use was evaluated. Additionally, the prognosis of the patients was evaluated according to whether the patients had delactation and recurrence. Therefore, we divided the above factors into three aspects for discussion: clinical manifestations, therapeutic effect and prognosis.
Clinical manifestations
Reddy et al. [15] compared MRSA- and MSSA-infected patients with postpartum mastitis, showing no significant differences in age, pregnancy history, initial symptoms or mode of delivery. Chen CY et al. [16] studied patients with breast abscesses caused by MRSA or MSSA infection, which suggested that MRSA infection did not increase the hospitalization rate of patients with breast abscesses. The results of our study showed no significant differences in hospitalization, postpartum time or age between the MRSA and MSSA groups, which is consistent with the above results.
Studies have shown that central breast abscesses, multiple abscesses and abscesses measuring > 5 cm are complex and refractory abscesses [17–19], which increase the difficulty of treatment. In our study, no significant differences were found in the location of the abscess, the number of abscess cavities or the amount of pus between patients with breast abscesses caused by MRSA infection or MSSA infection during lactation, which did not increase the difficulty of treatment. Although the results of our study were inconsistent with the above results, the sample size of the above studies was smaller than that of our samples and included some nonlactating breast abscess cases [19], which could have led to inconsistent results.
Therefore, based on our study, the clinical manifestations of patients with breast abscesses caused by MRSA infection during lactation were not different from those caused by MSSA infection, and MRSA infection did not increase the hospitalization rate, indicating that MRSA infection did not increase the severity of the breast abscess or the difficulty of treatment.
Therapeutic effect
With the development of minimally invasive treatment technology, ultrasound-guided needle aspiration and irrigation has become the preferred treatment method for breast abscesses and is widely used in clinical practice [20, 21]. Chen CY et al. [16] showed that MRSA infection did not reduce the therapeutic effect of ultrasound-guided percutaneous drainage or prolong the duration of treatment and antibiotic use compared with MSSA infection in postpartum breast abscess. In our study, 1222 patients were treated with ultrasound-guided needle aspiration and irrigation. Of these, 90 failed in the aspiration, including abscess ulceration after aspiration or ineffective aspiration; then, they underwent Mammotome minimally invasive vacuum-assisted biopsy, abscess catheter irrigation and drainage or abscess incision and drainage. However, the statistical analysis showed no difference in the therapeutic effect of needle aspiration between the MRSA and MSSA groups, and MRSA infection did not increase the failure rate of needle aspiration. The mean frequency of needle aspiration in the MRSA and MSSA groups was 3.0 and 2.9, respectively, without statistical significance, which also indicated that MRSA did not increase the frequency of needle aspiration. Among the 1222 patients, the treatment duration was 2–82 (mean, 8) days. The treatment duration was 7.9 days in the MRSA group and 8 days in the MSSA group, without statistically significant differences, indicating that MRSA infection did not prolong the treatment duration of patients with lactational breast abscesses. The above results are consistent with those of Chen CY et al [6]. Therefore, when clinicians treat MRSA-infected patients with breast abscesses during lactation, ultrasound-guided needle aspiration remains the first choice.
According to Jiayue Luo et al. [22], antibiotics were not routinely used for the treatment of breast abscesses during lactation, but the success rate was similar to that of routine antibiotic use. Thus, they are conducting a prospective randomized controlled study on whether breast abscesses during lactation should be treated with antibiotics during drainage. The participants were randomly divided into two groups: an antibiotic group (antibiotic use 5 days postoperatively) and a nonantibiotic group (no antibiotic use postoperatively). The authors will observe the treatment duration and recurrence rate of breast abscess. Their expected conclusion is that for the treatment of breast abscesses, the effect of drainage without antibiotics is not poorer than that of drainage combined with antibiotics. However, the study has not yet been completed, and the expected conclusion has not yet been confirmed. In our study, the symptoms were significantly relieved after needle aspiration or drainage, without antibiotic use. However, for the patients with severe systemic symptoms or poor effects of the puncture, antibiotics were administered. Among the 260 patients with MRSA infection, 82 were treated with antibiotics and the remaining 178 were not. Among the 82 patients receiving antibiotics, two were treated with vancomycin and the rest with levofloxacin. Of the 962 patients with MSSA infection, 305 were treated with antibiotics and 657 were not. The statistical analysis demonstrated no difference between the two groups, suggesting that MRSA infection in breast abscesses during lactation did not increase the use of antibiotics. All patients without antibiotic treatment were cured. Therefore, for the treatment of breast abscesses during lactation, effective drainage of pus might be necessary. Without drainage of infected fluid, the use of antibiotics is ineffective [23].
Prognosis
The study by Reddy et al. [15] showed that the delactation rate after mastitis in the MRSA group was 16% and that in the MSSA group was 22%, without statistical significance. However, our results showed that only delactation was significantly different between patients with breast abscesses during lactation in MRSA and MSSA groups. Among the 1222 patients, 28 in the MRSA group presented delactation, with a rate of 10.7% (28/260), whereas 63 (6.5%, 63/962) patients in the MSSA group showed delactation. The delactation rate in MRSA group was higher than that in MSSA group, which indicated that patients with breast abscesses infected with MRSA during lactation were more susceptible to delactation than those infected with MSSA. The authors think that this is related to the patients’ concern that MRSA infection would prolong the recovery time and their desire to prevent the recurrence of the abscess by delactation. Furthermore, delactation is also related to the mothers’ concern that MRSA could be transmitted to the child through her milk, leading to adverse effects for the child. These concerns increase the delactation rate of patients with breast abscesses infected with MRSA during lactation. A study in Taiwan [24] reported that the colonization rate of MRSA in the nasal cavity of healthy children was 8.1%, and breastfeeding could prevent the colonization of MRSA and MSSA in healthy children, which might be related to improvements in children’s immunity by breastfeeding. Therefore, breastfeeding can still be continued in patients with breast abscesses infected with MRSA during lactation. Acute mastitis and breast abscesses during lactation do not affect breastfeeding. The Academy of Breastfeeding Medicine [25] suggests that the first step in the treatment of mastitis during lactation is to effectively remove the milk, that is, encourage the mothers to breastfeed frequently and start from the affected side. After surgical drainage, breastfeeding on the affected breast should continue, even if a drain is present, with the proviso that the infant’s mouth does not come into direct contact with purulent drainage or infected tissue. Our results showed that patients in the MRSA group were more susceptible to delactation than those in the MSSA group, which differs from the findings of Reddy et al. [15]. This result might indicate the lack of adequate physician training in our department; that is, the proper education of patients about the condition is insufficient. Patients had a poor understanding of the disease and MRSA and had a fear of MRSA, thus leading to an increased delactation rate in the MRSA group. Therefore, we should also consider the psychological burden on the patients while undergoing treatment, so that the patients can correctly understand the disease and MRSA and eliminate their concerns, which might change the outcome.
In our study, 30 patients had abscess recurrence, including five in the MRSA group and 25 in the MSSA group, without a significant difference, which is consistent with the results of Chen CY et al. [16]. Their study showed that MRSA infection did not increase the hospitalization rate, frequency of outpatient follow-up, or recurrence rate compared with MSSA infection in postpartum breast abscess.
In conclusion, the infection and isolation rates of MRSA are increasing globally. Given the multiple drug resistance mechanism of MRSA, clinicians are more alert to these bacteria. Therefore, many doctors might believe that patients with breast abscesses infected by MRSA during lactation have a more serious condition and are difficult to treat. In terms of treatment options, they will intervene more actively for MRSA than for an MSSA infection. However, our study showed that age, postpartum time, location of abscess cavities, number of abscess cavities, frequency of needle aspiration, needle aspiration efficacy, treatment duration and recurrence were not significantly different between patients with breast abscesses that were infected by MRSA during lactation and those infected by MSSA, suggesting that MRSA infection does not increase the severity of breast abscess or the difficulty of treatment. For breastfeeding patients with breast abscesses, whether infected with MRSA or not, ultrasound-guided needle aspiration and irrigation should be the first-choice treatment[16]. For antibiotic use, if ultrasound-guided needle aspiration has a good effect in the patients with breast abscesses infected by MRSA during lactation, antibiotics are not necessary. If the treatment effect is not good, it can be combined with antibiotic use. According to the results of the bacterial culture, drugs sensitive to MRSA can be used.