What Causes Neonatal Mastitis?

Patient Presentation
A 15-day-old full-term female came to clinic with left breast swelling. Her mother said that the baby had some symmetric breast swelling after birth but that it had been resolving. She noticed the left breast swelling about 12 hours before and said that it seemed tender as the infant fussed more when it was touched. She denied any nipple discharge, fever, irritability, or feeding problems. There were no sick contacts. The past medical history showed a full-term infant born after an uneventful pregnancy and delivery. Maternal laboratories were negative and the infant received all routine care after delivery. She was exclusively breastfeed.

The pertinent physical exam showed an alert and responsive infant. Her weight was 3.960 kg (50%), length of 49 cm (25%) and head circumference of 34.5 cm (50%). She was afebrile. Her anterior fontanelle was soft and non-bulging. She had mild neonatal acne on both cheeks. Her right breast had a 1 cm breast bud that was palpable without overlying erythema. Her left breast had overlying erythema of a 3 cm symmetric mass centered under the nipple. The nipple was slightly retracted and purulent fluid was expressed. The area was warm. No axillary lymph nodes were palpable. The infant cried with palpation of the area but easily calmed. The diagnosis of neonatal mastitis was made and the infant was admitted for parenteral antibiotics and observation.

The laboratory evaluation showed a white blood cell count of 13.8 x 1000/mm2 with a 30% left shift. The C-reactive protein was < 0.5 mg/dl. Blood cultures were eventually negative. The nipple discharge gram stain showed gram-positive organisms and eventually grew only a few colonies of Staph. epidermidis. The patient’s clinical course after admission revealed that she continued to look and act well. She remained afebrile and was treated with 3 days of parenteral antibiotics. She was switched to oral antibiotics and monitored before being discharged. Over time she had marked resolution of the breast swelling and surrounding erythema and at 1 week followup she had a 1 cm left breastbud that was similar to the right breast.

Breast hypertrophy secondary to maternal hormones is common in neonates but neonatal mastitis is uncommon and relatively little is written in the literature. One study says “[m]ajor pediatric institutions can expect to see one to three cases per year.” Neonatal mastitis usually occurs between 2-8 weeks after birth in full term infants. Some studies report a peak occurence at 2-3 weeks and others at 4-5 weeks. It generally does not occur in preterm infants and this is thought to be because of underdeveloped breast tissue. Most studies report a higher incidence in females.

Symptoms include redness, swelling, induration, fluctuance, purulent nipple discharge and lymph node enlargement on the same side. Irritability as only sign has also been documented. Infants are often well appearing but may have fever and laboratory testing may show signs of infection such as increased white blood cell counts, and C-reactive protein levels.

Neonatal patients have an increased risk of abscess formation occurring in 40-50% of patients in some studies. Bacteremia has been reported in ~4% of patients. Bacterial meningitis is reportedly low, but lumbar puncture may be performed because of neonates age and symptoms.

Treatment is variable but most people recommend hospitalization and parenteral antibiotics especially because of the age and risk of abscess formation. Total antibiotic duration is variable but studies report 7-14 total days. Ultrasound examination for potential abscess and abscess treatment is commonly used. Surgical treatment for abscess formation includes a risk of decreased breast tissue, and scar formation.

Learning Point
The mechanism of neonatal mastitis is not fully understood but is thought to occur because of skin-colonizing bacteria migrating into the breast parchenyma. Staphylococcus aureus (methicillin-resistant and methicillin-sensitive) is the most common organism. A variety of other organisms have also been reported including S. epidermidis, E. coli, Klebsiella, Proteus, Pseudomonas and Aceinetobacter.

Questions for Further Discussion
1. What are indications for lumbar puncture?
2. How does sepsis and/or bacteremia present in neonates?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Breast Diseases.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Brown L, Hicks M. Subclinical mastitis presenting as acute, unexplained, excessive crying in an afebrile 31-day-old female. Pediatr Emerg Care. 2001 Jun;17(3):189-90.

Stricker T, Navratil F, Sennhauser FH. Mastitis in early infancy. Acta Paediatr. 2005 Feb;94(2):166-9.

Montague EC, Hilinski J, Andresen D, Cooley A. Evaluation and treatment of mastitis in infants. Pediatr Infect Dis J. 2013 Nov;32(11):1295-6.

Mohr EL, Berhane A, Zora JG, Suchdev PS. Acinetobacter baumannii neonatal mastitis: a case report. J Med Case Rep. 2014 Sep 25;8:318.

Stromps JP, Na HS, Grieb G, Orlikowsky T, Kuhl C, Pallua N. Surgical treatment of neonatal mastitis by periareolar drainage. Curr Pediatr Rev. 2014;10(4):304-8.

Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa Children’s Hospital