Characteristics and Incidence of Lactational Mastitis Using State-Wide Data from 2016 to 2022.

Objective: To estimate the characteristics and describe the incidence of lactational mastitis among postpartum people. Methods: We used Maine Health Data Organization's All Payer Claims Data for people who delivered during 2016-2022 with insurance coverage throughout pregnancy and 12 months postpartum and had a breast pump claim (as a proxy for breastfeeding) (N = 22520). We estimated the incidence of lactational mastitis within one year postpartum using International Classification of Diseases-Clinical Modification 10 diagnosis codes. We examined mastitis incidence by rurality of residence, delivery year, maternal age, parity (using a proxy measure), insurance type, pregnancy condition, and history of mastitis. We also assessed the timing and setting of the first mastitis diagnosis. Results: The incidence of lactational mastitis was 4.4% (95% CI: 4.1, 4.7). Persons with a higher incidence of mastitis included those living in metro areas (4.9%), 25-29 years old (4.6%), having commercial insurance coverage at delivery (5.0%), with their first or second delivery in the dataset (4.5%), and with a history of mastitis (13.9%). Overall, 15% of lactational mastitis was first diagnosed during an acute care encounter; however, this was higher among those living in isolated rural areas (22%), 20-24 years old (32%), having Medicaid insurance (24%), with three or more deliveries in the dataset (21%), and without a history of mastitis (18.5%). Conclusion: The incidence of diagnosed lactational mastitis varies by several maternal and pregnancy characteristics. Persons who are younger, live in rural areas, have Medicaid or have higher parity may face barriers to care in the primary care setting and ultimately be diagnosed with lactational mastitis during acute care encounters.