RT Book, Section A1 Shah, Ashish A1 Sobolewski, Brad A1 Mittiga, Matthew R. A2 Knoop, Kevin J. A2 Stack, Lawrence B. A2 Storrow, Alan B. A2 Thurman, R. Jason SR Print(0) ID 1181044277 T1 Neonatal Mastitis T2 The Atlas of Emergency Medicine, 5e YR 2021 FD 2021 PB McGraw-Hill PP New York, NY SN 9781260134940 LK accessemergencymedicine.mhmedical.com/content.aspx?aid=1181044277 RD 2024/10/05 AB Neonatal mastitis is an infection of the breast tissue that occurs in full-term neonates. The peak incidence of mastitis without abscess is in the 2nd week of life and the 4th week of life for mastitis with abscess. Females are affected more often than males in a 2:1 distribution. Clinically, it manifests as swelling, induration, erythema, warmth, and tenderness of the affected breast. The ipsilateral axillary lymph nodes may be swollen. Approximately 50% develop an abscess. In some cases, purulent discharge may be expressed from the nipple. Fever may be present in 25% of affected patients. Other systemic symptoms (irritability, decreased appetite, and vomiting) are less common but indicate a more severe infection if present. Bacteremia is rare. Staphylococcus aureus, specifically methicillin-resistant strains (MRSA), is the most common pathogen, causing 75% to 85% of cases. Rarely, gram-negative organisms or group B or D streptococci are the cause. If treatment is delayed, mastitis may progress rapidly with involvement of subcutaneous tissues and subsequent toxicity. In the initial stages, neonatal mastitis may mimic mammary tissue hypertrophy owing to maternal passive hormonal stimulation. Minor trauma, cutaneous infections, and duct blockage may precede this infection.