3 RESULTS
During study period, a total of 418 women were admitted to emergency department with a definite diagnosis of mastitis, finally, 267 patients were eligible for this study (Figure 1 ). The mean (± SD) age of the included patients was 27.5 (±2.40) years, with a range from 20 to 36 years. At presentation, 252 (94.4%) had breast redness, 234 (87.6%) had breast swelling, 251 (94.0%) had breast heat, 260 (97.4%) had severe pain in the breast, and 228 (85.4%) reported breast nodules/lumps. The characteristics of patients in the SELC and MELC groups are shown in Table 1 .
Antibiotics were prescribed to 200 (74.9%) patients, including 38 (14.2%) patients prescribed oral antibiotics and 162 (60.7%) patients prescribed intravenous antibiotics. Initial use of flucloxacillin, cephradine and clindamycin occurred in 186 (69.7%), 6 (2.2%) and 8 (3.0%) patients, respectively. The rates of initial antibiotic use in patients with SELCs and MELCs were 42.3% and 98.1%, respectively, p<0.001 (Table 2).
There were 33 (12.4%), 53 (19.8%) and 13 (5.2%) patients who did not perform therapeutic breast massage, who stopped breastfeeding or both, respectively; their counterparts consisted of 11 (9.9%), 25 (22.5%), and 6 (5.4%) patients with SELCs and 22 (14.1%), 28 (17.9%), and 7 (4.5%) patients with MELCs, respectively.
Among all 267 eligible patients, 230 (86.1%) patients returned to the hospital for review before or at the seventh day after initial treatment, and another 37 (13.9%) patients did not provide treatment outcomes by telephone.
The rate of treatment failure was 12.7% (34/267) in the overall population and 7.7% (12/156) in the MELC group. In the MELC group, only three patients did not receive an initial antibiotic but received subsequent antibiotics due to uncontrolled symptoms, and one of these patients developed a breast abscess. Of the remaining 153 patients, 9 patients developed breast abscesses.
The rate of treatment failure was 19.8% (22/111) in the SELC group, and treatment failures included 19 patients who were switched to antibiotic and 3 patients who had a change of their initial antibiotic. In 47 patients with initial antibiotic use, the rate of treatment failure was 6.4% (3/47), and in 64 patients without initial antibiotic use, the rate of treatment failure was 29.7% (19/64). The difference in patients with or without initial antibiotic use was significant (OR=4.207, 95% CI 1.318-13.424) (Table 3) .
The overall rate of breast abscess was 7.1% (19/267). The proportion was similar in each group: 8.1% (9/111) in the SELC group and 6.4% (10/156) in the MELC group. In the SELC group, the proportions were 2.1% (1/47) and 12.5% (8/64) when antibiotics were initially used or not used, respectively; the difference was not significant but showed an obvious trend (OR=6.571, 95% CI 0.793-54.481) (Table 3). All the breast abscesses were managed with repeat US-guided aspiration, and 84.2% (16/19) achieved complete resolution, while 15.8% (3/19) resorted to surgical drainage.
In the SELC group, the mean time until normal appearance of the breast and normal temperature was significantly shorter in patients with antibiotic use (3.8 ± 1.7 and 4.3 ± 2.1 days) than in those without antibiotic use (2.5 ± 1.1 and 3.0 ± 1.3 days), p<0.001 (Table 4 ).