Mastitis: prevalence, presentation, pathophysiology

Presenting signs and symptoms on the spectrum of breast inflammation in lactation commonly referred to as 'mastitis'

Mastitis means ‘inflammation of the breast’, but the definition of 'mastitis' still lacks international consensus.97 Despite diagnostic uncertainty, the presentation of breast inflammation which is most commonly meant when the word 'mastitis' is used remains a serious lactation-related problem.37

Used popularly, the diagnosis mastitis describes an erythematous painful lump in the breast, usually towards the outer part of the breast, with or without systemic symptoms of fever, myalgia, rigors, and fatigue.70, 98

The cluster of signs and symptoms commonly used to diagnose a mastitis emerge variably on a continuum of breast inflammation from mild to severe.36, 37 The NDC guidelines propose that breast inflammation, which encompasses mastitis, is more accurately described by clinical presentation rather than by terms which lack clear definition. A presentation of breast inflammation is described by selecting the relevant presenting signs and symptoms described in the table below.

Because of the highly subjective nature of fatigue, this symptom is not used in the NDC classification system.

Location of inflammation	Dimensions (millimetres)	Erythema	Pain	Systemtic signs + symptoms
Generalised - bilateral		None	None	Feels well
Generalised - unilateral		Mild	Mild when touched only	Fever
Localised WITHOUT lump		Moderate	Mild constant	Myalgia
Localised WITH lump		Severe	Moderate when touched only	Rigor
			Moderate constant
			Severe

Prevalence of mastitis

Breast pain is one of the most common reasons women give for premature weaning.1, 2

Prevalence data for mastitis is based upon variable definitions, in the absence of agreement about underlying mechanisms.98

• Wilson et al’s 2020 systematic review of incidence and risk factors for lactational mastitis, which included 26 articles, concluded that lactational mastitis affects about one in four women during the first 6 months postpartum. However, the authors note that the quality of studies is poor.101-105

• Mastitis appears to be the most common reason given for weaning in the first three weeks postbirth,105, 106.

• 70% of mastitis cases occur in the first 4 to 8 weeks.68, 107

• Although an episode of mastitis mostly occurs in just one breast, it may occur more than once, and on either side, and some women experience mastitis multiple times with the same child.

• Women who experienced mastitis with previous children are 2 to 4 times more likely to experience mastitis in subsequent lactations.98

• Because the incidence varies widely across locations, Wilson et al propose that mastitis, regardless of variable definitions, may be mostly preventable.101

When evaluating recent Australia data alone, the rate is at the higher end of the spectrum, at approximately 18% [2, 3].

The pathophysiology of mastitis in lactation: acute inflammation (unilateral and localised)

The NDC mechanobiological model of breast inflammation

You can find out about the mechanobiological model of breast inflammation here, which is, I have argued, the aetiological model which has the most robust evidence-base.

The link between nipple damage and mastitis is associative, not causative

There is an association between nipple damage and mastitis.

• Foxman et al’s 2002 prospective cohort study of 946 breastfeeding women found that the presence of nipple cracks and damage was linked with a three- to six-fold increase in the risk of mastitis.99

• In 2007 Kvist et al investigated 210 cases of lactation-related breast inflammation, finding that 36% of the women also had nipple damage. Although nipple damage was linked with slower resolution of inflammation, it was not linked with increased need for antibiotics.100

• In 2015 Cullinane et al showed that in 70 breastfeeding women who developed mastitis in the first 8 weeks post-birth, those who reported nipple damage had twice the incidence of mastitis.68

• In 2020 Wilson et al conducted a systematic review which investigated the incidence of and risk factors for mastitis, and found that cracked nipples were significantly associated with lactational mastitis in all 8 studies analysed.101

Engorgement, difficulties attaching the baby to the breast, and blocked ducts have also been associated with increased risk of mastitis.79, 101 Kvist et al found that women with breast inflammation who were using nipple shields had less favourable outcomes.100

Associations between breastfeeding problems and mastitis have been explained using the pathogenic model of breast inflammation, in which it is hypothesised that pathogenic bacteria, for example, Staphylococcus and Corynebacterium, enter the milk from nipple cracks to cause breast inflammation.68, 101

However, new evidence about the composition of the human milk microbiome, detailed here, demonstrates why it is unlikely that mastitis is caused by retrograde spread of ‘pathogenic’ bacteria from visible nipple damage.

• Bacteria and fungi identified on the nipple-areolar-complex in the presence of nipple pain and damage are also regularly identified in healthy human milk microbiomes.5, 96

• Most women with mastitis (64% in Cullinane et al) don’t have nipple damage 68

• Only a small proportion of nipple cracks and ulcers show signs of infection, and nipple damage is often not adjacent to the duct openings, but at the junction of the nipple and areola.

From the perspective of the gestalt biomechanical model of breastfeeding, nipple damage, breast inflammation, and difficulties bringing the infant on to the breast have a shared aetiology, which is nipple and breast tissue drag, or conflicting intra-oral vectors of force.Applying the gestalt model, nipple shield use is often an indicator of underlying and unresolved breast tissue drag and positional stability problems.

References

The references numbered in Mastitis: prevalence, presentation, pathophysiology and in Mastitis: management (including indication for antibiotics), side-effects, prevention are located in the research publication found here.

[2] Grzeskowiak LE, Kunnel A, Crawford SB, Cullinane M, Amir LH. Trends in clinical management of lactational mastitis among women attending Australian general practice: a national longitudinal study using MedicineInsight, 2011-2022. BMJ Open. 2024;14(5):e080128. doi: 080110.081136/bmjopen-082023-080128.

[3] Amir LH, Crawford SB, Cullinane M, Grzeskowiak LE. General practitioners' management of mastitis in breastfeeding women: a mixed method study in Australia. BMC Primary Care. 2024;25(161):https://doi.org/10.1186/s12875-12024-02414-12874.