Lactational Breast Abscesses Caused by Methicillin-Resistant or Methicillin-Sensitive Staphylococcus aureus Infection and Therapeutic Effect of Ultrasound-Guided Aspiration

Abstract

Background and Objective:

We investigated whether (1) there are any differences in lactational breast abscesses between patients from whom methicillin-resistant Staphylococcus aureus (MRSA) and those from whom methicillin-sensitive S. aureus (MSSA) were isolated from pus samples and (2) there are differences in the effects of ultrasound-guided aspiration.

Materials and Methods:

The clinical data of 171 patients with lactational breast abscesses treated by ultrasound-guided aspiration in Beijing from January to July 2018 were retrospectively analyzed. The patients were divided into MSSA infection (N = 132) and MRSA infection (N = 39) groups according to their bacterial culture results. Abscess cavity location, abscess cavity number, maximum abscess cavity size, antibiotic utilization rate, and cure rate were compared between the groups. Cure rate refers to the proportion of the total number of cases remaining after the elimination of failed cases. The number of ultrasound-guided aspiration procedures performed for healing between the two groups was also compared.

Results:

There were no significant differences in abscess cavity location, abscess cavity amount, and abscess cavity size between both groups. The antibiotic utilization rate of the two groups were 58.3% (MSSA, 77/132) and 69.2% (MRSA, 27/39), respectively, and there were no significant differences between both groups. The cure rates of ultrasound-guided aspiration of the two groups were 97.7% (MSSA, 129/132) and 92.3% (MRSA, 36/39), and there were no significant differences between both groups. There were also no significant differences in the median number of aspiration performed for cure between the MRSA infection group (median = 3, range = 1–10) and the MSSA infection group (median = 3, range = 1–14).

Conclusion:

Lactational breast abscesses are the same irrespective of the type of S. aureus infection. Treatment by ultrasound-guided aspiration for patients with MRSA infection can achieve the same effect as that for those with MSSA infection.

Introduction

Lactational mastitis is a common disease among lactating women. If a well-defined area of the breast remains hard, red, and tender despite appropriate management, then an abscess should be suspected and diagnostic breast ultrasound will identify a fluid collection.¹ Approximately 3% of patients with lactational mastitis eventually develop breast abscess,² with the most common type of causative pathogenic bacteria being Staphylococcus aureus. In recent years, the incidence of methicillin-resistant S. aureus (MRSA) infection has been on the rise and it has been reported that MRSA is the most common organism seen in breast abscesses in some countries such as Pakistan and Italy.^3,4

MRSA is known as a “superbug” because it shows multidrug resistance, thereby making infections difficult to control.⁵ In recent years, MRSA has been attributed to an estimated 5,400 extra deaths and more than one million extra days of hospitalization.⁶ In the global priority list of antibiotic-resistant bacteria to guide research, discovery, and development of new antibiotics published by the world health organization in 2017, the highest ranked Gram-positive bacteria (high priority) were vancomycin-resistant Enterococcus faecium and MRSA.⁷

Therefore, the treatment of lactational mastitis with MRSA infection is often more radical. Incision and drainage with postoperative antibiotic drugs has been suggested as the treatment of choice for these abscesses based on their pathogenesis.⁸ Some guidelines recommend that incision and drainage should be performed together with the administration of broad-spectrum antibiotics as a treatment strategy for patients with MRSA-caused skin and soft tissue infections combined with abscess formation,^9,10 but it is unknown if this applies to breast abscesses that are special case of abscess.

So far, many studies have confirmed the advantages of ultrasound-guided aspiration for the treatment of lactational breast abscess.^11–14 Ultrasound-guided fine-needle aspiration to extract pus and repeated flushing of abscess cavity with normal saline have been widely performed owing to their advantages of low pain, low weaning rate, and no obvious postoperative scar. However, this treatment was not widely adopted in China yet and incision and drainage was still widespread in many hospitals of China.¹⁵

Even though some hospitals have adopted ultrasound-guided aspiration as the primary treatment for lactational breast abscess, doctors are still concerned about if this applies to patients with MRSA infection.

However, there are almost no studies that have focused on the characteristics of the pathogenic bacteria and the effect of ultrasound-guided aspiration on patients with lactational breast abscesses caused by MRSA infection.

Therefore, in this study, we retrospectively collected all the cases of lactational breast abscesses treated by ultrasound-guided aspiration as well as compared the characteristics of the breast abscesses caused by methicillin-sensitive S. aureus (MSSA) and those caused by MRSA as well as the effect of ultrasound-guided abscess aspiration on patients with lactational breast abscesses.

All the cases were treated by ultrasound-guided aspiration under local anesthesia, the frequency and interval of aspiration and whether to use antibiotics were determined by the doctor depending on the patient's condition. Not all patients were treated with antibiotics, especially those with mild symptoms, as the Chinese government had instituted strict regulations to prevent the misuse of antibiotics. Clinical commonly used antibiotics include cephalosporins, clindamycin, quinolones, and occasionally vancomycin.

Materials and Methods

Patients

All cases in the registry of lactational breast abscesses treated by ultrasound-guided aspiration between January and July 2018 at the Center for Prevention and Treatment of Breast Diseases, Maternal and Child Health Hospital, Haidian District, Beijing, were reviewed through the electronic medical record system.

Inclusion criteria

Patients with lactational breast abscesses who were treated by ultrasound-guided aspiration and pus culture showed bacteria.

Exclusion criteria

Patients with negative culture results or rare bacteria except S. aureus or MRSA were excluded. Cases with <1-month follow-up were also excluded.

Follow-up

Patients were followed up through regular outpatient review for 1 month.

This study was approved by the local ethics committee.

Treatment

After local anesthesia, a 14-gauge fine needle was used to extract pus from abscess cavity under ultrasound guidance, and the abscess cavity was repeatedly rinsed with normal saline until the flush solution was clear. Patients with a large amount of pus underwent aspiration once daily, whereas those with a small amount of pus underwent aspiration every 2 days or several days, until a cure was achieved. During the treatment of lactational mastitis (including before and after abscess formation), the doctor decided whether to use antibiotics depending on the patient's condition, but no standard protocol was followed.

Diagnostic standards and other clinical criteria

The diagnostic criteria for breast abscesses formed during lactation were as follows: 1.

Inflammation such as redness, swelling, heat, and pain in the breast sometimes accompanied by fever

Sensation of fluctuation experienced in the diseased area on physical examination

Mixed echo or no echo area seen in the breast by ultrasound, and liquid flow is more likely to be seen after the probe is pressurized.

Lactating women were diagnosed based on any of the aforementioned criteria, and pus was extracted by aspiration.

The clinical criteria for cure⁵ had to comply with all of the following four items:

The pain was relieved.

Normal body temperature, subsidence of redness and swelling in the diseased area of the skin, and no obvious tenderness

Aspiration fluid is clear and thin.

No recurrence of symptoms and signs during 1-month follow-up.

Treatment was considered a failure if symptoms did not improve or if abscess bursted after aspiration.

Central region: It is located in the areola region.

Multicavity: ≥2 abscess cavities are classified as multicavity abscesses.

Abscess cavity size: Abscess diameter was the largest diameter of abscess cavity measured by ultrasound before the first aspiration. According to the convention of grouping in literature reports,¹³ the diameter of 5 cm of abscess cavity was used as the dividing line for grouping comparison.

Statistical analysis

According to bacterial culture results, bacteria were divided into MSSA infection and MRSA infection groups. Chi-square test was performed for comparing abscess cavity location, abscess cavity number, abscess cavity size, and antibiotic utilization rate between both groups. The cure rate of the ultrasound-guided aspiration in both groups was compared with chi-square test with the four-grid table. After treatment failure cases were eliminated, nonparametric tests were performed to compare the number of aspiration performed for treatment of both groups. The test level alpha was set at 0.05. The SPSS 21.0 statistical software was applied for statistical analysis.

Results

In this study, 215 women with lactational breast abscess treated with ultrasound-guided aspiration were retrospectively analyzed. A total of 171 cases of MSSA and MRSA infections were included after removing 36 cases in which no bacteria were isolated and 8 cases that involved other rare bacteria.

The characteristics of abscess formation in the two groups were compared, that is, abscess cavity location (whether it was located in the central region), abscess cavity number (whether it was multicavity abscess), abscess cavity size (whether maximum abscess diameter was >50 mm). Results are summarized in Table 1.

Table 1.

Comparison of the Characteristics of the Lactational Mammary Abscess Caused by Methicillin-Sensitive Staphylococcus aureus Infection and Methicillin-Resistant Staphylococcus aureus Infection

	MSSA (n = 132)		MRSA (n = 39)		p
	Cases	Proportion (%)	Cases	Proportion (%)	p
Location of abscess					0.884
Central region^a	29	22	9	23.1
Noncentral region	103	78	30	76.9
No. of abscess cavity					0.411
Single cavity	100	75.8	32	82.1
Multicavity^b	32	24.2	7	17.9
Size of abscess cavity^c					0.143
>5 cm	88	66.7	21	53.8
≤5 cm	44	33.3	18	46.2

Central region is located in the areola region.

Multicavity: ≥2 abscess cavities are classified as multicavity abscesses.

Abscess diameter was the largest diameter of abscess cavity measured by ultrasound before the first aspiration.

MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-sensitive Staphylococcus aureus.

Antibiotics utilization rate was compared between the two groups: 77 patients in the MSSA infection group received antibiotic treatment (58.3%, 77/132). In the MRSA infection group, 27 patients received antibiotic treatment (69.2%, 27/39). Comparisons using chi-square test showed a p-value of 0.221.

Regarding comparison of cure rate between the two groups, the MSSA infection and MRSA infection groups showed three treatment failure cases, with cure rates of 97.7% (129/132) and 92.3% (36/39), respectively.

Regarding chi-square test and comparison using the four-grid table, p-value was found to be 0.106.

Regarding comparison of the number of aspiration performed for treatment, three failed cases in each group were eliminated. Furthermore, 129 patients in the MSSA infection group and 36 in the MRSA infection group were treated by ultrasound-guided aspiration. Results of the nonparametric tests are shown in Table 2.

Table 2.

Comparison of the Number of Punctures Performed for Healing in the Methicillin-Sensitive Staphylococcus aureus Infection Group and Methicillin-Resistant Staphylococcus aureus Infection Group

	MSSA	MRSA	Nonparametric test
Total number (n)	129	36
Minimum no. of punctures	1	1
Maximum no. of punctures	14	10
The median value	3	3
Z			−0.709
P			0.478

MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-sensitive Staphylococcus aureus.

Discussion

Lactational mastitis is frequently reported among lactating women, and some of them develop breast abscesses. In recent years, the proportion of MRSA infections has been on the rise. Owing to the characteristics of severe symptoms, high incidence of breast abscess, and long course of the disease, clinical treatment is often more radical. In a report from Taiwan, 21% (11/52) cases of MRSA-induced breast abscesses required treatment conversion to incision and drainage.¹⁶ Although many studies have confirmed that ultrasound-guided aspiration of lactational breast abscesses is a better treatment modality than incision and drainage, some doctors are still full of questions and concerns about whether the treatment will work for patients with MRSA.

The findings of our study showed that there were no significant differences between the MSSA infection group and the MRSA infection group with regard to abscess site, number of abscess cavities, and size of abscess cavity. Under the premise that there was no significant difference in antibiotic utilization rate, ultrasound-guided aspiration was performed; the cure rate of the MSSA infection group was 97.7% and the cure rate of the MRSA infection group was 92.3%, there was no statistical difference between the two groups. Moreover, there was no statistical difference between the two groups in terms of the number of aspiration performed. Therefore, there is no sufficient evidence to prove that lactational breast abscesses caused by MRSA infection is more complicated or more difficult to treat than those caused by MSSA infection.

This study has a few limitations. This study was a retrospective study with a small number of cases. Antibiotic use and the aspiration frequency during treatment were determined according to the clinical experiences of different doctors, and there was no standard protocol, which may affect the study results. The viewpoints stated in this study need to be verified in future prospective studies with large samples and more detailed and unified standards.

Conclusion

Our study shows that lactational breast abscesses caused by MSSA infection show the same characteristics as those caused by MRSA infection. Moreover, the treatment effect of ultrasound-guided aspiration was similar in abscesses caused by either MSSA or MRSA infection. Furthermore, our study shows that for patients with lactational breast abscesses diagnosed with MRSA infection, ultrasound-guided aspiration should be preferred over incision and drainage because of its several advantages.

Footnotes

Acknowledgments

We thank the Chinese Center for Disease Control and Prevention and Maternal and Child Health Center for financial support.

Disclosure Statement

No competing financial interests exist.

Funding Information

Project support: 2017 Chinese Center for Disease Control and Prevention, Maternal and Child Health Center, Heshengyuan Maternal and Child Nutrition and Health Research Project. Project No. 2017FYH011. Project name: Study on the correlation between breast feeding and respiratory and digestive infections in infants infected with methicillin-resistant Staphylococcus aureus.

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