Comment: The certainty of the evidence is upgraded by large magnitude of effect.
A systematic review and meta-analysis «Lai BY, Yu BW, Chu AJ, et al. Risk factors for lactation mastitis in China: A systematic review and meta-analysis. PLoS One 2021;16(5):e0251182. »4 included 14 studies involving 8032 Chinese participants. Significant risk factors included improper milking method (OR 6.79, 95% CI 3.45 to 13.34), repeated milk stasis (OR 6.23, 95% CI 4.17 to 9.30), the first 6 months postpartum (OR 5.11, 95% CI 2.66 to 9.82), postpartum rest time less than 3 months (OR 4.71, 95% CI 3.92 to 5.65), abnormal nipple or crater nipple (OR 3.94, 95% CI 2.34 to 6.63), improper breastfeeding posture (OR 2.47, 95% CI 2.09 to 2.92), little or no nipple cleaning (OR 2.05, 95% CI 1.58 to 2.65; PAR 24.73%), primipara (OR 1.73, 95% CI 1.25 to 2.41), low education level (OR 1.63, 95% CI 1.09 to 2.43), cesarean section (OR 1.51, 95% CI 1.26 to 1.81), and postpartum mood disorders (OR 1.47, 95% CI 1.06 to 2.02).
A case–control study «Mediano P, Fernández L, Rodríguez JM et al. Case-control study of risk factors for infectious mastitis in Spanish breastfeeding women. BMC Pregnancy Childbirth 2014;(14):195. »3 among breastfeeding women (368 women with mastitis, 148 controls) assessed potential predisposing factors of mastitis. The variables significantly- and independently-associated with mastitis were cracked nipples (P < 0.0001), oral antibiotics during breastfeeding (P < 0.0001), breast pumps (P < 0.0001), topical antifungal medication during breastfeeding (P = 0.0009), mastitis in previous lactations (P = 0.0014), breast milk coming in later than 24 h postpartum (P = 0.0016), history of mastitis in the family (P = 0.0028), mother-infant separation longer than 24 h (P = 0.0027), cream on nipples (P = 0.0228) and throat infection (P = 0.0224).
In a prospective cohort study with questionnaire and telephone follow-up «Kinlay JR, O'Connell DL, Kinlay S. Risk factors for mastitis in breastfeeding women: results of a prospective cohort study. Aust N Z J Public Health 2001 Apr;25(2):115-20. »1, 1 075 breastfeeding women were recruited and were sent follow-up questionnaires at three, eight and 26 weeks post-delivery. Mastitis occurred in 20% (95% CI 18 to 22%) of women during the first six months. Factors that were statistically significantly and independently related to mastitis were: past history of mastitis (adjusted Hazard Ratio=1.74, 1.07 to 2.81), university or college education (HR=1.93, 1.18-3.16), blocked duct (HR=2.43, 1.68-3.49), cracked nipples (HR=1.44, 1.00-2.07), use of creams on nipples (HR=1.83, 1.22 to 2.73), particularly papaya cream (Relative Risk = 1.83, 1.36 to 2.47), and always starting with the alternate breast on consecutive feeds (HR=2.28, 1.50 to 3.44).
A study «Foxman B, D'Arcy H, Gillespie B et al. Lactation mastitis: occurrence and medical management among 946 breastfeeding women in the United States. Am J Epidemiol 2002;155(2):103-14. »2 in USA followed 946 breastfeeding women by telephone interviews at 3, 6, 9, and 12 weeks postpartum. 9.5% reported provider-diagnosed lactation mastitis at least once. Adjusted odds ratios (OR) for mastitis wer: history of mastitis with a previous child (OR 4.0, 95% CI 2.64 to 6.11), cracks and nipple sores in the same week as mastitis (OR 3.4, 95% CI 2.04 to 5.51), using an antifungal nipple cream in the same 3-week interval as mastitis (OR 3.4, 95% CI 1.37 to 8.54), and using a manual breast pump (OR 3.3, 95% CI 1.92 to 5.62) strongly predicted mastitis. Feeding fewer than 10 times per day was protective (OR 0.6, 95% CI 0.41 to 1.01).