Mastitis and breast abscess in infants younger than two months

INTRODUCTION — The clinical features, evaluation, and management of mastitis and breast abscess in infants <2 months will be discussed in this topic review. Mastitis and breast abscess are less common in infants ≥2 months than in younger infants. The evaluation and management of mastitis in infants ≥2 months are similar to those in older children. Mastitis and breast abscess in older children and adolescents, lactational mastitis, and breast infections in adult women are discussed separately.

●(See "Mastitis and breast abscess in children and adolescents".)

●(See "Lactational mastitis".)

●(See "Nonlactational mastitis in adults".)

●(See "Primary breast abscess".)

MICROBIOLOGY — Most cases of mastitis and breast abscess in infants are caused by Staphylococcus aureus [1-8]. Less common causes include gram-negative enteric organisms (eg, Escherichia coli, Salmonella), anaerobes, and group B Streptococcus (Streptococcus agalactiae) [1,4,6,7,9-13].

PATHOGENESIS — The pathogenesis of infant mastitis typically involves spread of pathogenic bacteria from the skin and/or mucous membranes to the breast parenchyma through the nipple [3,5,14]. In infants with systemic infection (which is usually gram-negative), bacteria also may spread to the breast hematogenously.

Predisposing factors include stimulation of the breast by placental and maternal hormones (estrogens), which result in physiologic breast hypertrophy in full term infants, and maternal skin or soft-tissue infection in the postpartum period [3,13,15,16]. It is thought that premature babies have underdeveloped mammary glands, which are less likely to develop infection [4]. Breast massage may also increase risk [17].

CLINICAL FEATURES — During the first year of life, mastitis typically occurs in full-term infants who are younger than two months. Peak incidence of mastitis appears to occur earlier (at two weeks of life) than mastitis with abscess (four weeks of life) [2,18].

During the first two weeks of life, mastitis occurs with equal frequency in males and females [2,3]. Thereafter, it is more common in females, with a female:male ratio of approximately 2:1 [3]. A possible explanation for the predominance in females is the tendency for breast hypertrophy to persist longer than in males [2,4].

Mastitis in infants usually is unilateral and remains localized [1-4,7]. Characteristic clinical features include marked erythema, tenderness, and induration of the affected breast (picture 1) [1]. There may be associated skin lesions (eg, pustules, bullae) [17,18]. The axillary lymph nodes may be enlarged and tender [5,19]. More than one-half of infants with mastitis develop abscesses, which can be indicated by fluctuance [5,7,18,20]. Purulent nipple discharge occurs in approximately 20 percent of cases [7].

Systemic symptoms also may occur and may indicate more severe infection. In a retrospective multicenter cohort of 657 infants ≤90 days of age with mastitis, systemic symptoms included fever in 21 percent and poor feeding or fussiness in 10 percent [8]. Among the 10 infants with a clinical diagnosis of sepsis or shock, 8 were febrile, 2 were ill appearing, and 2 were neither febrile nor ill appearing.

Gastrointestinal symptoms may indicate Salmonella or other gram-negative enteric pathogens [3,5].

COMPLICATIONS — Although infant mastitis usually is uncomplicated, cases of infant mastitis complicated by extensive cellulitis, necrotizing fasciitis, and osteomyelitis have been reported [3,4,21-25].

Spread of infection beyond the breast is uncommon in well-appearing infants [3,7]. In a series of 94 infants (0 to 120 days) with mastitis, two infants had a positive urine culture; both had systemic findings: A febrile infant with a breast culture positive for S. aureus also had group B Streptococcus isolated from the urine, and an irritable infant with a breast culture positive for coagulase negative Staphylococcus (a possible contaminant) also had E. coli isolated from the urine [7]. Two infants had positive cerebrospinal fluid (CSF) findings: One ill-appearing infant with methicillin-resistant S. aureus breast abscess also had submental abscesses and CSF pleocytosis and was treated for meningitis; the other had CSF culture positive for Klebsiella oxytoca without pleocytosis; repeat culture was negative.

DIAGNOSIS — A clinical diagnosis of mastitis can be made in infants with swelling, erythema, warmth, tenderness, induration, and/or fluctuance of the breast (picture 1). Fluctuance indicates breast abscess. Ultrasonography is not necessary but can confirm the diagnosis of mastitis or breast abscess if the diagnosis is uncertain [26,27].

Laboratory evaluation is not necessary to make the diagnosis but helps to guide additional evaluation and management. (See 'Additional evaluation' below and 'Management' below.)

DIFFERENTIAL DIAGNOSIS — In infants younger than two months, the main consideration in the differential diagnosis of mastitis is physiologic breast hypertrophy, which resolves spontaneously [28]. In contrast to mastitis, physiologic breast hypertrophy usually is bilateral and symmetric (picture 2); the breasts are neither erythematous nor tender; if present, the nipple discharge is milky rather than purulent and does not contain polymorphonuclear white blood cells or bacteria on Gram stain. (See "Breast masses in children and adolescents", section on 'Neonates and infants'.)

Other considerations in the differential diagnosis of mastitis and breast abscess in infants include hemangioma and lymphangioma (cystic hygroma). (See "Infantile hemangiomas: Epidemiology, pathogenesis, clinical features, and complications", section on 'Clinical presentation' and "Vascular lesions in the newborn", section on 'Lymphatic malformations'.)

ADDITIONAL EVALUATION — Our suggested evaluation for infants with mastitis includes:

●Complete blood count with differential – The white blood cell (WBC) count can help determine the need for lumbar puncture and urine culture; if elevated at baseline, the WBC count may be used to monitor response to therapy, particularly if the infant does not improve as expected.

In a retrospective multicenter cohort of 657 infants with mastitis, the median peripheral WBC count was 15,600/microL (interquartile range 12,900 to 19,500/microL) [8]. The WBC count was ≥15,000/microL in the only infant with concomitant meningitis, 6 of 10 infants with a clinical diagnosis of sepsis or shock, and all 3 infants with concomitant urinary tract infection. In a retrospective series of 41 patients with neonatal mastitis, the WBC count was elevated (>15,000 WBC/microL) in 46 percent [3].

●Blood culture – Blood culture results help to guide antimicrobial therapy if a pathogen is identified.

In a retrospective multicenter cohort of 657 infants with mastitis, blood cultures were obtained in 581 (88 percent) [8]. Two infants (0.3 percent) had bacteremia: one with methicillin-resistant S. aureus (MRSA) and one with group B Streptococcus; both grew MRSA from site cultures. Both infants were <28 days of age and neither was febrile, ill appearing, or had a WBC count ≥15,000/microL. Contaminants were isolated from 25 blood cultures (4.3 percent). In earlier studies, blood cultures were positive in approximately 4 percent of cases but potential contaminants were included [3,18-20,29-31].

●Gram stain and culture – If possible, we also try to isolate the pathogen directly from the breast infection. We perform Gram stain and culture (aerobic and anaerobic) of nipple drainage (if present) and of abscess fluid (in infants with breast abscess as indicated by fluctuance) [3,6,7]. The abscess fluid sample may be obtained by aspiration (with or without ultrasonographic guidance) or incision and drainage [3,7,30,32]. (See 'Drainage of breast abscess' below.)

In a multicenter cohort of 657 infants ≤90 days with mastitis (median age 21 days), site cultures were obtained in 335 (51 percent) [8]. Approximately 80 percent of cultures were positive (54 percent for MRSA, 29 percent for methicillin-susceptible S. aureus, and 8 percent for unspecified S. aureus). A smaller case series had similar results [7].

●Lumbar puncture if clinically indicated – We perform cerebrospinal fluid (CSF) cell counts, differential, Gram stain, and culture if clinically indicated [3,14,19]; our indications for lumbar puncture in infants with mastitis who are <2 months of age include (any of the following) [3,8,23]:

•Ill appearance (eg, poor appetite, lethargy, abscess)

•Temperature ≥38°C [100.4°F] or, for infants <28 days, subjective report of fever at home (eg, "tactile temperature" or "felt warm")

•WBC count ≥15,000/microL or ≤5000/microL

Positive CSF cultures are rare in infants with mastitis. In a multicenter retrospective study of 657 infants ≤90 days with mastitis (median age 21 days), CSF cultures were obtained in 216 (33 percent) and positive in only one [8]. The six-day-old infant was febrile but not described as ill appearing, grew MRSA from the CSF and site culture, and had a peripheral WBC count of 24,600/microL, a CSF WBC count of 44/microL, and a CSF red blood cell count of 15,600/microL.

Neonates and young infants with S. aureus mastitis (particularly methicillin-resistant S. aureus strain USA300) may have substantial CSF pleocytosis with sterile CSF cultures, whether or not they have systemic symptoms [30]. If CSF is obtained after initiation of antimicrobial therapy, the culture may be unreliable, and infants with mastitis-related pleocytosis may receive unnecessary treatment for meningitis.

The evaluation of the febrile or ill-appearing infant is discussed separately. (See "Approach to the ill-appearing infant (younger than 90 days of age)" and "The febrile infant (29 to 90 days of age): Outpatient evaluation", section on 'Focal infection' and "The febrile neonate (28 days of age or younger): Outpatient evaluation and initial management", section on 'Focal infection'.)

●Urine culture if clinically indicated – We obtain a catheterized urine specimen for culture in infants <28 days of age with WBC counts ≥15,000/microL and temperature ≥38°C [100.4°F] or subjective fever.

In a retrospective multicenter cohort of 657 infants with mastitis, urine culture was obtained in 274 (42 percent) [8]. Three infants, all <28 days of age, had a concomitant urinary tract infection. Two infants were febrile and all three had WBC counts ≥15,000/microL. In one, the site culture and urine both isolated E. coli. In the other two infants without site cultures, the urine pathogens were Klebsiella and E. coli.

MANAGEMENT

Supportive care — Supportive care for infants with mastitis includes application of warm compresses. Caregivers should be discouraged from palpation of the breast and expression of fluid from the nipple.

Drainage of breast abscess — In addition to antimicrobial therapy, breast abscess may require aspiration and/or incision and drainage (for both diagnosis and treatment), unless spontaneous drainage occurs [2,3,32,33].

During drainage, care must be taken to avoid the breast bud [5,33,34]. If incision and drainage is necessary, it should be performed by appropriately trained personnel (eg, a breast surgeon, breast radiologist, or pediatric surgeon) because of the potential for breast hypoplasia or scarring after this procedure [3,4]. (See "Breast disorders in children and adolescents", section on 'Breast asymmetry'.)

Antimicrobial therapy

Route of empiric therapy — We initiate treatment for mastitis in infants <2 months parenterally because of the potential for progression to abscess with oral treatment and the prevalence of community-associated methicillin-resistant S. aureus (CA-MRSA) [2,3,7,30]. One small series noted that all five patients who were treated with oral amoxicillin-clavulanate before presentation developed breast abscesses despite susceptibility to amoxicillin-clavulanate [2].

No randomized controlled studies have evaluated antibiotic regimens for infant mastitis. Our recommendations for treatment are based upon the frequency of causative pathogens and the response to therapy described in observational studies [2,7,18,30,35].

Choice of regimen

●Severe complications, including extensive cellulitis, necrotizing fasciitis, osteomyelitis, and shock – For infants <2 months with mastitis or breast abscess and severe complications, including cellulitis (cellulitis extending beyond the skin overlying the breast bud), necrotizing fasciitis, osteomyelitis, and shock, we provide parenteral antimicrobial therapy with broad empiric coverage for methicillin-resistant S. aureus (MRSA), methicillin-susceptible S. aureus, and gram-negative organisms. For example (table 1) [30]:

•For infants with normal cerebrospinal fluid (CSF) profile:

-Vancomycin plus nafcillin plus ceftriaxone (if the infant is not also receiving or expected to receive calcium-containing intravenous [IV] fluids or parenteral nutrition), or

-Vancomycin plus nafcillin plus gentamicin

•For infants with abnormal CSF profile:

-Vancomycin plus nafcillin plus cefotaxime (if available), or

-Vancomycin plus nafcillin plus ceftazidime, or

-Vancomycin plus nafcillin plus ceftriaxone (if the infant is not also receiving or expected to receive calcium-containing IV fluids or parenteral nutrition)

IV ceftriaxone should be avoided in neonates who are also receiving or expected to receive calcium-containing IV fluids or parenteral nutrition because of the potential for life-threatening adverse drug reactions [36].

Therapy should be altered according to culture results once they are available. Treatment of invasive MRSA infections is discussed separately. (See "Staphylococcus aureus in children: Overview of treatment of invasive infections", section on 'Treatment of neonates'.)

●No severe complications – For infants <2 months with mastitis or breast abscess without severe complications, the initial parenteral regimen is guided by the Gram stain, if one is available, and local susceptibility patterns (table 1) [2,3,19,28,30]. Therapy should be altered according to culture results once they are available.

•Gram-positive cocci – If gram-positive cocci are identified, empiric therapy should include coverage for S. aureus (table 1).

-In communities where CA-MRSA infections are rare, a penicillinase-resistant antibiotic (eg, oxacillin or nafcillin) may be used.

-In areas with an increased incidence of CA-MRSA (more than 10 percent of community isolates), vancomycin or clindamycin is appropriate [30]. Clindamycin may be used if central nervous system infection is not a concern (table 1). (See "Staphylococcus aureus in children: Overview of treatment of invasive infections", section on 'Treatment of neonates'.)

•Gram-negative organisms – If gram-negative organisms are identified, empiric therapy should include an aminoglycoside (eg, gentamicin, amikacin) or third-generation cephalosporin (eg, cefotaxime, ceftriaxone, ceftazidime). Cefotaxime (preferred if available), ceftriaxone, or ceftazidime is recommended if CSF is abnormal (table 1). Intravenous ceftriaxone should be avoided in infants who are also receiving or are expected to receive intravenous calcium in IV fluids or parenteral nutrition [36].

•Gram stain not available or no organisms seen – If the Gram stain is not available or if no organisms are seen, we provide empiric coverage for S. aureus and gram-negative enteric organisms (table 1) [4,6,30].

Duration of therapy — The duration of therapy depends upon the clinical response; a total of 7 to 14 days (parenteral and oral) is usually adequate [2,3,18,30].

Infants with uncomplicated mastitis or breast abscess may be transitioned from parenteral to oral therapy if all of the following criteria are met:

●Resolution of systemic symptoms and fever

●Improvement in other clinical findings

●Antibiotic susceptibility results are available

●Systemic bacterial cultures (blood, CSF) isolate no pathogens after 48 hours of incubation

Infants receiving oral antibiotics should be followed closely (eg, by phone, virtual, and/or office visits) to assess medication adherence and response to therapy; treatment failure may be an indication for abscess drainage (or repeat drainage). One retrospective study of neonates with skin and soft tissue infections discharged with oral antibiotics found only 3 of 46 infants (6 percent) had treatment failure. All pathogens were clindamycin-resistant S. aureus [16,30,37]. (See 'Response to therapy' below.)

RESPONSE TO THERAPY

Monitoring response — Response to therapy is indicated by clinical improvement within 24 to 48 hours of appropriate antibiotic therapy.

Failure to respond — For infants who worsen or fail to improve after 48 hours of initial therapy, possible explanations include:

●Inadequate drainage (if drainage was performed), abscess recurrence, or development of a new abscess

●Inadequate empiric therapy (for those with negative cultures or in whom cultures were not obtained)

●Alternative diagnosis (eg, physiologic breast hypertrophy, hemangioma, lymphangioma) (see 'Differential diagnosis' above)

Ultrasonography may identify residual, recurrent, or new abscesses that require drainage, particularly if induration makes it difficult to assess fluctuance, and can be used to guide the drainage procedure [38]. Ultrasonography also may be helpful in identifying alternative diagnoses. (See 'Drainage of breast abscess' above.)

If cultures remain negative (or were not obtained) and ultrasonography does not identify lesions that require drainage or alternative diagnoses, a change in empiric therapy may be indicated (eg, to include activity against methicillin-resistant S. aureus [MRSA] if it was not included initially or for less common pathogens if MRSA coverage was initially included) [6,30,32,33]. In such cases, consultation with an expert in infectious diseases is suggested.

PROGNOSIS — There are few data regarding the long-term outcome of mastitis [2]. Most patients have an excellent prognosis, but there are case reports of breast asymmetry following incision and drainage for breast abscess during infancy [1,4,39]. Recurrences are rare, but patients should be followed closely [3]. Patients with S. aureus mastitis are at risk for subsequent S. aureus infections at other sites [30]. (See "Methicillin-resistant Staphylococcus aureus infections in children: Epidemiology and clinical spectrum".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Skin and soft tissue infections".)

SUMMARY AND RECOMMENDATIONS

●Most cases of mastitis and breast abscess in infants are caused by Staphylococcus aureus. Less common causes include gram-negative enteric organisms, anaerobes, and group B Streptococcus. (See 'Microbiology' above.)

●During the first year of life, mastitis typically occurs in infants younger than two months of age. A clinical diagnosis of mastitis can be made in infants with characteristic clinical findings: unilateral swelling, erythema, warmth, tenderness, and/or induration of the breast (picture 1). Fluctuance indicates breast abscess. Ultrasonography is not necessary but can confirm the diagnosis of mastitis or breast abscess if the diagnosis is uncertain. Systemic findings (eg, fever, poor feeding) are an indication of more severe disease. (See 'Clinical features' above and 'Diagnosis' above.)

●We obtain a complete blood count with differential and blood culture before the initiation of antimicrobial therapy. We also obtain Gram stain and culture of nipple drainage (if present) and abscess fluid (if abscess is present). We obtain cerebrospinal fluid (CSF) in infants <2 months who are ill-appearing (eg, poor appetite, lethargy, abscess), febrile (≥38°C [100.4°F]) or subjective fever if <28 days of age, or have white blood cell count ≥15,000/microL or <5000/microL. (See 'Additional evaluation' above.)

●Breast abscess may require aspiration and/or incision and drainage in addition to antimicrobial therapy unless spontaneous drainage occurs. Incision and drainage should be performed by appropriately trained personnel (eg, a breast surgeon, breast radiologist, or pediatric surgeon). (See 'Drainage of breast abscess' above.)

●In infants <2 months of age with mastitis or breast abscess, we provide initial antimicrobial therapy parenterally. (See 'Antimicrobial therapy' above.)

•For infants with mastitis or breast abscess and severe complications (eg, cellulitis extending beyond the skin overlying the breast bud, necrotizing fasciitis, osteomyelitis, and shock), we provide parenteral antimicrobial therapy with broad empiric coverage for methicillin-resistant S. aureus, methicillin-susceptible S. aureus, and gram-negative organisms (eg, vancomycin plus nafcillin plus one of the following: gentamicin, cefotaxime, ceftazidime, or ceftriaxone). Intravenous ceftriaxone should be avoided in infants who are also receiving or are expected to receive intravenous calcium in intravenous fluids or parenteral nutrition because of the potential for life-threatening adverse drug reactions. (See 'Choice of regimen' above.)

•The empiric antibiotic regimen for infants without severe complications is determined by the Gram stain (if available) and local susceptibility patterns (table 1). Therapy should be altered according to culture results once they are available. (See 'Choice of regimen' above.)

●Most patients have an excellent prognosis. However, there are case reports of breast asymmetry following incision and drainage for breast abscess during infancy. Recurrences are rare. (See 'Prognosis' above.)