Infectious mastitis and breast abscess are the result of the introduction of bacteria from the infant's mouth and/or throat to the mother's breast. The usual infecting organism is Staphylococcus aureus, although it may also be Staphylococcus epidermidis and streptococci.

Initially, there may be underlying cellulitis in the connective tissue, caused by a blocked duct or poor milk drainage.

Epidemiology

• Between 2% and 33% of breast-feeding women develop lactation mastitis.¹
• The incidence is highest in the first few weeks postpartum, decreasing gradually after that.²
• However, cases may occur as long as the woman is breast-feeding.

Risk factors

Women with a past history of mastitis have an increased risk.³There is consensus that nipple fissures, cracks and sores are predisposing factors for mastitis; however, the role of feeding frequency is unclear.
Lactation mastitis has also been linked to:

• Primiparity.
• Stress.
• Improper nursing technique, leading to incomplete emptying of the breast.⁴

Presentation

Mastitis is diagnosed based on clinical symptoms and signs indicating inflammation - breast pain, myalgias and fever.

Symptoms

• This normally presents ≥1 week postpartum with only one breast usually affected and often only one quadrant or lobule painful to touch, inflamed, swollen and hot.
• It should be distinguished from congestive mastitis (breast engorgement) which usually presents on the second or third day of breast-feeding. The complaint is of a swollen and tender breast which is often bilateral and without fever or erythema.

Signs

• Breast examination reveals unilateral oedema, erythema in a wedge-shaped area, and tenderness.
• There may be purulent drainage or pus obtained on aspiration.
• Axillary lymphadenopathy is palpable.

In a breast abscess, examination reveals a tender hard breast mass, which may be fluctuant, with overlying erythema.

Investigations

Detection of pathogens in breast milk is not always possible, and the results of milk culture may not be a useful guide for therapy.
The agents most frequently identified in milk culture are S. aureus and coagulase-negative Staphylococcus spp.⁴ However, these may be contaminants or skin flora.

Management

General advice

Be aware that many women may require emotional support.⁵

• Assessment of breast-feeding technique by an appropriately trained, skilled person who can assess feeding pattern, positioning, attachment, sucking behaviour and breast fullness.
• Advise manual expression of milk to empty the breast after feeding; this allows proper drainage of the breast.
• Reassure the mother that continuing to breast-feed does not present any risk to the infant.
• Suggest supportive therapy such as bedrest, increased fluids, ice packs, analgesia and use of anti-inflammatory agents.
• If the woman is not wishing to continue breast-feeding, advise tight breast binding, ice packs and prevention of breast stimulation to suppress lactation and reduce pain.
• Advise that she should stop breast-feeding if an abscess develops, although feeding is encouraged to restart once the abscess is treated.²

Pharmacological treatment

Antibiotics, e.g. flucloxacillin or erythromycin should be prescribed.

Surgical

• Incision and drainage of abscess with cavity packed open with gauze.
• Parenteral antibiotics should be administered at the same time, with added coverage for anaerobic bacteria.
• Needle aspiration of the abscess, repeated every other day until the pus no longer accumulates, has been suggested as an alternative to open drainage.⁶
• Any persisting mass will need further investigation to exclude sinister causes.

Complications

Serious complications occur in cases where treatment is delayed, incorrect or ineffective. These include breast abscess and sepsis:

• Breast abscesses have been reported in 5% to 11% of mastitis cases.⁷
• A case of toxic shock syndrome was reported in Japan, secondary to postpartum mastitis caused by methicillin-resistant S. aureus (MRSA).⁸

Document references

1. Foxman B, D'Arcy H, Gillespie B, et al; Lactation mastitis: occurrence and medical management among 946 breastfeeding women in the United States. Am J Epidemiol. 2002 Jan 15;155(2):103-14. [abstract]
2. Barbosa-Cesnik C, Schwartz K, Foxman B; Lactation mastitis. JAMA. 2003 Apr 2;289(13):1609-12.
3. Kinlay JR, O'Connell DL, Kinlay S; Risk factors for mastitis in breastfeeding women: results of a prospective cohort study. Aust N Z J Public Health. 2001 Apr;25(2):115-20. [abstract]
4. Mastitis: Causes and Management, World Health Organization (2000)
5. Amir LH, Lumley J; Women's experience of lactational mastitis--I have never felt worse. Aust Fam Physician. 2006 Sep;35(9):745-7. [abstract]
6. Dixon JM; Repeated aspiration of breast abscesses in lactating women. BMJ. 1988 Dec 10;297(6662):1517-8.
7. Marshall BR, Hepper JK, Zirbel CC; Sporadic puerperal mastitis. An infection that need not interrupt lactation. JAMA. 1975 Sep 29;233(13):1377-9. [abstract]
8. Fujiwara Y, Endo S; A case of toxic shock syndrome secondary to mastitis caused by methicillin-resistant Staphylococcus aureus. Kansenshogaku Zasshi. 2001 Oct;75(10):898-903. [abstract]

Internet and further reading

• Mastitis, Clinical Knowledge Summaries (May 2010)
• Wong AJ et al; Pregnancy, Postpartum Infections, eMedicine, Apr 2010

Acknowledgements