Table 1.

Studies Included in the Review (N = 26).

Study # Author (Date Published)	Study Design	Setting (Date of Study)	Sample	Definition of Mastitis	Data Collection	Disease Frequency
						Numerator	Denominator	Results
1 Amir et al. (2006)	case control	Melbourne, AU (2002–2004)	N = 199 Cases = 100 2 maternity hospitals Controls = 99 BF no mastitis in community health centers	> 2 breast signs or symptoms & one systemic symptom present > l2 hr	Questionnaire cases at time of mastitis care & controls at 6 weeks PP			Unable to be calculated
2 Amir et al. (2007)	cohort	Melbourne, AU (2000–2001)	N = 1,193 from 2 hospitals	> 2 breast signs or symptoms & systemic symptom present > l2 hr	Structured phone interview at 6 mo.	n = mastitis episodes	n = of BF weeks	17.3% (n = 206) 95% CI [15.2–19.5]
3 Axelsson & Blomberg (2014)	cohort	Sweden (2009–2010)	N = 6682 1 year	Not stated, mastitis treated by antibiotics & those not treated	8 weeks PP, self-report questionnaire sent by post	n = mastitis	N	316 (4.7%) (1.8% = treated & 2.9% = not treated)
4 Cullinane et al. (2015)	cohort	Melbourne, AU (2009–2011)	N = 346 nulliparas from 2 hospitals intending to BF > 8 weeks	> signs or symptoms & one systemic symptom present > 12 hr	Self-administered questionnaires in hospital & Weeks 1, 2, 3, 4 & 8 PP	n = mastitis	N with complete follow up	70 (20%) 97 episodes/ 70 women; 71 during 4 weeks PP
5 Elfgen et al. (2017)	case control	Germany	N = 255 Cases = 85 from sexual abuse support centers Controls = 170 from kindergartens	Not stated	A semi structured interview > 3 hr & questionnaire	Women with mastits 33 Cases, 42 Controls	85 Cases, 170 Controls	Mastitis Cases = 38.8% Controls = 24.7% o
6 Evans & Heads (1995)	cohort	Australia (1992–1993)	N = 16,531 All women in 8 maternity hospitals	Breast pain, swelling, erythema, fever	Data collection form filled out by a nurse during clinical visits	n = cases of mastitis	50% of births (assumed 50% BF rate)	519 (6.35%)
7 Fetherston (1998)	case control	Australia	N = 156 Cases = 78 Controls = 78 matched baby’s age & mother’s previous BF	Elevated T, systemic illness with pink, tender, hot, swollen > 24 hr	Questionnaire after each episode of mastitis & 3 months PP f/u			Disease frequency unable to be calculated
8 Fetherston (1997)	cohort	Australia	N = 306 215 private & 91 public hospital BF mothers	Elevated T, systemic illness with pink, tender, hot, swollen > 24 hr	Phone calls q 4 weeks during 3 months	n = mastitis episodes	N	83 (27.1%) 63 participants /83 mastitis episodes
9 Foxman et al. (2002)	cohort	Michigan & Nebraska, USA (1994–1998)	N = 946 birthing center in Michigan & large company in Nebraska with an employee BF program	Self-report of mastitis diagnosed by a health care provider	Interviews at 3, 6, 9 & 12 weeks or until weaning	n = mastitis episodes	N	90 (9.5%)
10 Jonsson & Pulkkinen (1994)	cohort	Finland	N = 664 from 24 outpatient PP clinics	physicians/ nurses	questionnaire 5–12 weeks PP	Not clear	Not clear	24%
11 Kaufmann & Foxman (1991)	cohort	Michigan, USA (1984-1985)	N = 966 BF Hospital births	Physician’s diagnosis	Medical record	N = mastitis < 7 weeks	# of women–weeks at risk (estimated)	4.12/1,000 women-weeks 7 week risk = 2.9%
12 Khanal et al. (2015)	cohort	Rupandehi District, Nepal (2014)	N = 338 15 rural areas & 12 urban areas randomly selected	> 2 breast symptoms & > 1 ‘‘flu-like symptoms’’	questionnaires during Months 1, 4, & 6 PP	n = mastitis during first 30d PP	N	27 (8.0%) 95% CI [5.1– 10.8]
13 Kinlay et al. (2001)	cohort	Newcastle, AU (1994)	N = 1,075 singleton 2 hospitals planned to BF	Painful red area & T > 38°C or systemic symptoms or a diagnosis from an HCP	Mail questionnaires at 3, 8 & 26 weeks PP			219 (20%)
14 Kinlay et al. (1999)	cohort	Newcastle, AU (1994)	N = 1075 singleton 2 hospitals planned to BF	Painful red area & T > 38 °C or systemic symptoms or a diagnosis from an HCP	Mail questionnaires at 3, 8 & 26 weeks PP	n = women with mastitis	N	219 (20%)
15 Kvist et al. (2013)	cross-sectional	Denmark (2011)	N = 90 lactation specialists at conference	Any combination of breast tension, erythema, pain & fever	Questionnaire	n = babies where mastitis occurred	N = BF babies	40 (18%)
16 Marshall et al. (1975)	cohort	California, USA (1971–1973)	N = 2,534 a medical center BF	Red, tender area & T = > 38 °C	Diagnosis by physician	n = mastitis	N	61 (2.5%; 65 episodes)
17 Mediano et al. (2014)	case control	Spain (2009–2011)	N = 516 Cases = 368 Controls = 148 healthy BF	Cases Laboratory analysis	Questionnaire			Disease frequency unable to be calculated
18 Nicholson & Yuen (1995)	cohort	Melbourne, AU (1988–1991)	N = 785 in hospital initially BF contacted at 3 months	Not stated	Phone interview or mail questionnaire at 3 months Post-discharge	n = mastitis	N	7.7%
19 Ohene-Yeboah (2008)	cross-sectional	Kumasi, Ghana (2004–2006)	N = 1612 breast care center; complaint of breast pain	Not stated	A full clinical examination	n = mastitis	N	189 (11.8%)
20 Potter (2005)	cohort	Cotswold & Vale PCT, UK (2002)	N = 218 Geographical area	T = > 38 °C, breast painful to touch, wedge-shaped hot reddened area	Self-report mail questionnaire at 6 mo. PP	n = mastitis	N	88 (40%) cases 32 (15%) said they had mastitis
21 Prentice & Lamb (1985)	community-based	Gambia	N = unknown all BF during 16 months	4-point scale of severity of symptoms	Based on judgement of medical staff.	n = 65 episodes/ 40 women	Not reported	M incidence = 2.6%
22 Riordan & Nichols (1990)	cross-sectional	USA	N = 91 attendees at 2 BF conferences	Breast soreness and redness, flu like aching, & T > 100.4 °F	Self-administered questionnaire	n = mastitis with most recent child	N	“One-third”
23 Scott et al. (2008)	cohort	Glasgow, Scotland (2004–2005)	N = 420 in hospital & BF	Red, tender, hot, swollen with T ≥ 38 °C ) or systemic symptoms or diagnosis for > 24 hr	Phone f/u at 3, 8, 18 & 26 weeks or weaning	n = women with mastitis	N	74 (18%) 95% CI [14–21]
24 Tang et al. (2014)	cohort	Jiangyou, PRC (2010–2011)	N = 670 single healthy babies 7 health facilities & BF	Red, tender, hot, swollen area with T ≥ 38 °C ) or systemic symptoms or diagnosis by HCP for > 24 hr	1 face-to-face interview; f/u phone interviews at 1, 3- & 6-months PP	n = mastitis episodes	n = weeks of BF	10.3% (69 episodes) 95% CI [8.0–12.6] 42 > 1 episode = 6.3% (95% CI [4.5–8.1])
25 Vogel et al. (1999)	cohort	Auckland, New Zealand (1996)	N = 350 healthy infants in hospital 94% were followed up to 1 year PP	maternal report or breast infection	Interview at hospital. Phone interviews at 1, 2, 3, 6, 9, & 12 months PP	n = women with mastitis	N	83 (23.7%) 123 mastitis episodes
26 Zarshenas et al. (2017)	cohort	Shiraz, Iran (2014–2015)	N = 672 maternity wards of 5 hospitals	Red, tender, hot, or swollen area with an T ≥ 38 °C ) or systemic symptoms	Clinic f/u at 1, 3, 4, & 6 months PP	n = mastitis episodes	n = women BF weeks	130 (19.3%) 95% Cl [16.3–22.3]

Note: BF = breastfeeding; T = temperature; PP = postpartum; HCP = healthcare provider; f/u = follow up; q=every; breast signs and symptoms = pain, redness or lump; systemic symptom = fever or “flu-like” symptoms.