Mastitis is an inflammatory disease of the breast, which may be accompanied or not infection. It is associated with breastfeeding, so it also is known as lactational mastitis or puerperal mastitis. Occasionally, it can be fatal if it is inadequately managed. Breast abscess, a localized collection of pus within the breast, is a serious complication of mastitis. Recent investigations suggest that mastitis may increase the risk of HIV transmission through breastfeeding. mastitis symptoms