What are the causes, clinical presentation, diagnostic evaluation, and recommended management of mastitis in postpartum lactating women and in non‑lactating patients?

Mastitis: Causes, Clinical Presentation, Diagnosis, and Management

Definition and Epidemiology

Mastitis is breast inflammation that may or may not involve infection, occurring most commonly in lactating women during the first 3 months postpartum with an incidence of approximately 10-11% in the United States. 1, 2

• Non-lactating mastitis can occur at any age, including in males, though it is far less common 3
• The pooled incidence rate is 11.1 episodes per 1000 breastfeeding weeks at 0-25 weeks postpartum 1

Causes and Pathophysiology

Lactational Mastitis

• Most cases (80-86%) are inflammatory rather than infectious, with 14-20% resolving spontaneously without antibiotics 4
• When infection occurs, Staphylococcus aureus is the predominant pathogen, followed by Streptococcus species 5, 6
• Community-acquired MRSA is an emerging pathogen in mastitis, particularly in healthcare workers and areas with high MRSA prevalence 7
• Risk factors include milk stasis from poor infant latch, overstimulation of milk production, tissue trauma from aggressive breast massage, and nipple fissures 2
• Approximately 10% of mastitis cases progress to breast abscess formation 8

Non-Lactating Mastitis

• Less common and requires broader differential diagnosis including inflammatory breast cancer 3

Clinical Presentation

Typical Symptoms

• Focal breast tenderness with overlying skin erythema or hyperpigmentation 2
• Fever (often >38.5°C) and systemic symptoms including malaise and chills 1, 8
• Rapid onset, typically within the first few months postpartum 1
• Unilateral presentation is most common 2

Red Flag Symptoms Requiring Urgent Evaluation

• Symptoms persisting beyond 1 week of appropriate antibiotics may indicate inflammatory breast cancer and warrant urgent evaluation within 48 hours 4
• Erythema occupying at least one-third of breast surface or peau d'orange appearance requires urgent ultrasound and possible biopsy 4
• Fever and chills despite outpatient antibiotics indicate systemic involvement and potential sepsis risk 8, 9

Diagnostic Evaluation

Clinical Diagnosis

• Diagnosis is made clinically without routine laboratory tests or imaging in uncomplicated cases 2
• Based on presence of fever, malaise, focal breast tenderness, and overlying skin changes 2

When to Obtain Additional Testing

• Milk cultures should be considered to guide antibiotic therapy, particularly in non-responsive cases or when MRSA is suspected 2
• Ultrasound is indicated for:
  • Immunocompromised patients 2
  • Worsening or recurrent symptoms 2
  • Suspected abscess formation (approximately 10% of cases) 8
  • Symptoms persisting beyond 1 week of appropriate treatment 4

Management Algorithm

Initial Conservative Management (Days 1-2)

Begin with a 1-2 day trial of conservative measures before initiating antibiotics, as most mastitis is inflammatory rather than infectious. 4, 2

• NSAIDs for pain and inflammation 4
• Ice application to affected breast 4
• Continued breastfeeding or milk expression from the affected breast - this is essential and discontinuing worsens the condition 4, 8, 9
• Avoid overstimulation: no excessive pumping, heat application, or aggressive breast massage, as these exacerbate inflammation 9, 2

When to Initiate Antibiotics

Add narrow-spectrum antibiotics if symptoms do not improve within 12-24 hours of conservative management. 4

First-Line Antibiotic Therapy

Dicloxacillin 500 mg orally four times daily is the preferred agent for methicillin-susceptible S. aureus. 4

• Alternative: Cephalexin 500 mg orally four times daily, particularly useful for penicillin-allergic patients 4
• Both agents are safe during breastfeeding with minimal milk transfer 4, 9
• Duration: typically 10-14 days (though specific duration not explicitly stated in guidelines)

MRSA Coverage Indications

Consider MRSA-active antibiotics for:

• High local MRSA prevalence 4
• Previous MRSA infection 4
• Failure to respond to first-line beta-lactam antibiotics within 48-72 hours 4
• Healthcare workers or other high-risk populations 7

Hospitalization Criteria

Admit patients with:

• Fever and chills persisting despite outpatient antibiotics, indicating systemic involvement 8, 9
• Concern for sepsis 4, 8
• Need for IV antibiotics when oral therapy fails 9

Hospital management includes:

• IV antibiotics targeting S. aureus 8
• Access to breast pump if prolonged separation from infant occurs 8
• Trained breastfeeding support staff 8
• Continued breastfeeding or milk expression 8

Management of Breast Abscess

If abscess develops (10% of cases):

• Perform ultrasound-guided needle aspiration as preferred drainage method 9
• Breastfeeding can continue on the affected side provided the infant's mouth does not contact purulent drainage 8, 9

Critical Pitfalls to Avoid

• Never discontinue breastfeeding - this worsens mastitis and increases abscess risk 8, 9
• Avoid overstimulation, excessive pumping, heat, and aggressive massage - these exacerbate inflammation 9, 2
• Avoid trimethoprim-sulfamethoxazole (TMP-SMX) in infants ≤28 days old or those with jaundice, prematurity, or G6PD deficiency due to bilirubin displacement risk 4
• Avoid doxycycline, metronidazole, and TMP-SMX in pregnancy 9
• Avoid methotrexate during breastfeeding due to potential accumulation in neonatal tissues 4
• Do not delay treatment in non-responsive cases, as this may lead to abscess formation 8

Special Populations

Pregnancy

• Dicloxacillin, cephalexin, clindamycin, and azithromycin are safe with no documented teratogenic effects 9
• Same management principles apply with continued breastfeeding 9

Non-Lactating Women

• Broader differential diagnosis required, including inflammatory breast cancer 3
• Lower threshold for imaging and biopsy if symptoms persist 4