Most Common Cause of Mastitis During Breastfeeding
The most common cause of lactational mastitis is Staphylococcus aureus infection, though many cases begin as inflammatory mastitis secondary to milk stasis rather than true bacterial infection. 1, 2, 3
Primary Causative Organisms
- Staphylococcus aureus is the predominant bacterial pathogen in infective mastitis, with most strains being resistant to beta-lactamase sensitive antibiotics 1, 2
- Streptococcal species can also cause mastitis, though this is much less common 4
- Methicillin-resistant S. aureus (MRSA) is becoming an increasingly important pathogen as community prevalence rises 2
Pathophysiology: Inflammation vs. Infection
Most cases of mastitis begin as inflammatory conditions secondary to milk stasis, not true bacterial infections. 3 This is a critical distinction that affects treatment:
- Ineffective milk removal and milk stasis create the initial inflammatory response 5, 3
- Ineffective positioning of the baby at the breast or restricted feeding patterns contribute to milk stasis 5
- Secondary bacterial infection may develop if the inflammatory process is not resolved 1, 3
Risk Factors That Precipitate Mastitis
- Nipple trauma (fissures, cracks) serves as a portal of entry for bacteria 1, 4
- Overstimulation of milk production through excessive pumping 3
- Tissue trauma from aggressive breast massage 3
- Poor infant latch technique 2
- Infant mouth anomalies (cleft palate) that impair effective milk removal 2
Clinical Implications for Management
The inflammatory vs. infectious distinction is crucial because:
- A 1-2 day trial of conservative measures (NSAIDs, ice, direct breastfeeding, minimizing pumping) is often sufficient without antibiotics 3
- Antibiotics should be reserved for cases that don't improve with conservative management 3
- When antibiotics are warranted, dicloxacillin or cephalexin targeting S. aureus are first-line choices 1, 2
- Milk cultures should be obtained to guide antibiotic therapy, particularly in non-responsive cases 1, 3
Important Caveats
- Approximately 10% of mastitis cases progress to breast abscesses requiring drainage 6, 7, 2
- Breastfeeding should continue during mastitis treatment as effective milk removal is essential for resolution 6, 8, 7, 1, 2
- The infant can safely breastfeed from the affected breast unless their mouth would contact purulent drainage 6, 8