An Update on the Recognition and Management of Lactational Breast Inflammation

Christine M. Betzold, NP, CLC, MSN

Disclosures

J Midwifery Womens Health. 2007;52(6):595-605. 

In This Article

Differential Diagnosis: Infectious versus Noninfectious Mastitis

When a woman presents with breast discomfort, the clinician must consider not only causes specifically related to lactation, but also conditions unrelated to lactation. Conditions range from those that are fairly benign, such as costochondritis, or normal physiologic processes, such as breast fullness, or life-threatening disorders, such as neoplasms. Additionally, skin infections can mimic breast infections. There is one case report of a mother with streptococcal necrotizing fasciitis that first appeared to be mastitis ( Table 1 ).[13]

While some breast conditions are easy to discern, the most common lactational breast complaints (engorgement, plugged or blocked ducts, noninfectious and infectious mastitis) are challenging and sometimes impossible to differentiate. The difficulty is explained by the theory that they are a continuum with indistinct boundaries.[14] These processes not only have indistinct boundaries, but each process has some element of milk stasis or obstructed drainage. Thus, noninfectious breast inflammation may also be simply defined as "milk stasis" secondary to ineffective or obstructed milk removal.[14] In addition, when breast milk is obstructed, irrespective of the cause, the paracellular pathways open, resulting in increased levels of sodium and chloride,[14,15,16] decreased levels of lactose and potassium, and leakage of inflammatory cytokines.[2,14] In fact, even after milk stasis is corrected, the milk tastes less sweet and more salty for about a week,[2] and infants have been known to prefer the unaffected side.[17] More significantly, the leakage of inflammatory cytokines can provoke fever, chills, and muscle aches, clinically mimicking an infectious process. Therefore, the presence of systemic symptoms adds to the confusion about whether or not the mother is experiencing symptoms caused by milk stasis-related inflammation and/or infection.[14,17] Additionally, even if the symptoms were initially solely related to milk stasis, a secondary infection can then compound the outcome.

Differentiation is further confounded by the finding that low bacterial counts, which should indicate noninfectious mastitis, are common even when pathogens are cultured from breast milk. One explanation for this phenomenon is that milk expression may dilute the pathogens as milk released from uninfected areas mixes with milk from the infected area. Likewise, the infected area may block the extraction of the pathogen, thereby lowering the number or organisms.[14] This may explain why in one case report, a woman with < 103 of bacterial growth still developed an abscess.[14] Another possible explanation is that the antibacterial properties of human milk may destroy pathogens.[14] Furthermore, we cannot assume that when breast inflammation resolves without antibiotics it was therefore noninfectious. It is possible that adequate breast drainage may have effectively flushed out the pathogen, or that the maternal immune response was capable of independently clearing infection, or perhaps some breast inflammation is related to an as yet undocumented pathogen.[14] Conversely, when infectious mastitis is inadequately treated or treatment is delayed, its bacterial origin may declare itself, especially when it results in an abscess.

In summary, because of indistinct boundaries, milk stasis, and the presence of inflammatory cytokines, infectious and noninfectious processes imitate each other. Additionally, the lack of reliable laboratory tests increase the challenge of differentiating these processes. Table 2 assists with assessment by comparing and contrasting the most common breast disorders.

Both infectious and noninfectious mastitis can present without significant redness, fever, or systemic symptoms, yet symptoms may be so severe as to require intravenous antibiotics and hospitalization. While infectious mastitis typically presents with a fever > 38.5°C, flu-like symptoms, the classic wedge-shaped area of localized tenderness, and warmth and redness of one breast, noninfectious mastitis can also present with these symptoms. However, infectious mastitis is more likely to persist for more than 24 hours, be bilateral, or elicit high fever and/or produce significant breast discomfort.

Milk stasis (or any event that creates milk stasis) is an explicit risk factor for the development of breast inflammation. Events that can cause milk stasis include insufficient drainage of the breast, rapid weaning, oversupply of milk, pressure on the breast (e.g., from a poor-fitting bra or binding of the breasts), a blocked duct, or feedings that are missed, scheduled, infrequent, or timed.[2,3] One other predisposing factor that most authorities generally agree upon is skin breakdown of the nipple (e.g., fissures, cracks, or blisters), although they are "neither essential nor sufficient to cause infection."[18] A damaged nipple is more likely to be a risk factor if it is colonized by S aureus.[3] Unfortunately, in the first month postpartum, one study documented that more than half of women have nipples colonized with S aureus.[19] The mode of transmission of S aureus to the nipple may include colonization with virulent bacteria before leaving the hospital[2] or from the mother's own nasal or skin flora.[17,18] Eczema may be a risk factor for infection, because women with eczema are more likely to harbor S aureus.[20,21]

Additionally, risk factors for colonization with methicillin-resistant S aureus (MRSA) include cesarean birth, administration of antibiotics during labor, birth, or the early postpartum period, and multiple gestations.[22] Another potential risk factor is in vitro fertilization, which necessitates that mothers have repeated exposures to the health care system.[23,24] Evidence suggests that community-acquired MRSA has become a health care-associated pathogen.[25] Although evidence is inconclusive, maternal fatigue or stress, anemia, poor nutrition, and maternal or infant illnesses have all been associated with mastitis.[2,3] Finally, one should always consider inflammatory breast cancer as a potential underlying factor.[26]

When infectious mastitis does occur, S aureus and coagulase-negative staphylococci (CoNS) are the bacteria most frequently cultured from breast milk.[2,17] While the presence of CoNS may simply be a skin contaminant,[2] CoNS cultured from the milk of women diagnosed with mastitis has been found to cause acute mastitis in mice.[17] Another known pathogen is Streptococcal infection, which should be suspected whenever bilateral mastitis presents early postpartum.[17] Other documented microorganisms are Bacteroids spp., Escherichia coli, or other gram-negative bacteria, group A and group B hemolytic streptococci, Peptostreptococcus spp., Mycobacterium tuberculosis (rare), and Candida spp. (rare).[2,17] Mixed infections also occur.[2,17] Additionally, the clinician should consider the possibility of community-acquired MRSA (CA-MRSA), because the incidence is on the rise,[24] even in persons who lack traditional risk factors (Figure 1).[25]

Mother with mastitis and an abscess caused by community-acquired methicillin-resistant Staphylococcus aureus breastfeeding after ultrasound-guided needle aspiration of the abscess.

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