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Int Breastfeed J. 2008 Apr 7;3:6. doi: 10.1186/1746-4358-3-6.

The role of bacteria in lactational mastitis and some considerations of the use of antibiotic treatment.

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Department of Obstetrics and Gynaecology, Helsingborg Hospital, 251 87, Sweden.
Department of Nursing, Karlstad University, 651 88, Sweden.
Department of Nursing, Gjovik University College, Norway.
Department of Clinical Microbiology and Immunology, University Hospital, Lund, Sweden.
Contributed equally



The role of bacterial pathogens in lactational mastitis remains unclear. The objective of this study was to compare bacterial species in breast milk of women with mastitis and of healthy breast milk donors and to evaluate the use of antibiotic therapy, the symptoms of mastitis, number of health care contacts, occurrence of breast abscess, damaged nipples and recurrent symptoms in relation to bacterial counts.


In this descriptive study, breast milk from 192 women with mastitis (referred to as cases) and 466 breast milk donors (referred to as controls) was examined bacteriologically and compared using analytical statistics. Statistical analyses were also carried out to test for relationships between bacteriological content and clinical symptoms as measured on scales, prescription of antibiotics, the number of care contacts, occurrence of breast abscess and recurring symptoms.


Five main bacterial species were found in both cases and controls: coagulase negative staphylococci (CNS), viridans streptococci, Staphylococcus aureus (S. aureus), Group B streptococci (GBS) and Enterococcus faecalis. More women with mastitis had S. aureus and GBS in their breast milk than those without symptoms, although 31% of healthy women harboured S. aureus and 10% had GBS. There were no significant correlations between bacterial counts and the symptoms of mastitis as measured on scales. There were no differences in bacterial counts between those prescribed and not prescribed antibiotics or those with and without breast abscess. GBS in breast milk was associated with increased health care contacts (p = 0.02). Women with >/= 10(7) cfu/L CNS or viridans streptococci in their breast milk had increased odds for damaged nipples (p = 0.003).


Many healthy breastfeeding women have potentially pathogenic bacteria in their breast milk. Increasing bacterial counts did not affect the clinical manifestation of mastitis; thus bacterial counts in breast milk may be of limited value in the decision to treat with antibiotics as results from bacterial culture of breast milk may be difficult to interpret. These results suggest that the division of mastitis into infective or non-infective forms may not be practically feasible. Daily follow-up to measure the subsidence of symptoms can help detect those in need of antibiotics.

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