title: Determinants of mastitis in women in the CASTLE study: a cohort study.
abstract: BACKGROUND
  Mastitis is an acute, debilitating condition that occurs in approximately 20 % of breastfeeding women who experience a red, painful breast with fever. This paper describes the factors correlated with mastitis and investigates the presence of Staphylococcus aureus in women who participated in the CASTLE (Candida and Staphylococcus Transmission: Longitudinal Evaluation) study. The CASTLE study was a prospective cohort study which recruited nulliparous women in late pregnancy in two maternity hospitals in Melbourne, Australia in 2009-2011.
  
  
  METHODS
  Women completed questionnaires at recruitment and six time-points in the first eight weeks postpartum. Postpartum questionnaires asked about incidences of mastitis, nipple damage, milk supply, expressing practices and breastfeeding problems. Nasal and nipple swabs were collected from mothers and babies, as well as breast milk samples. All samples were cultured for S. aureus. "Time at risk" of mastitis was defined as days between birth and first occurrence of mastitis (for women who developed mastitis) and days between birth and the last study time-point (for women who did not develop mastitis). Risk factors for incidence of mastitis occurring during the time at risk (Incident Rate Ratios [IRR]) were investigated using a discrete version of the multivariable proportional hazards regression model.
  
  
  RESULTS
  Twenty percent (70/346) of participants developed mastitis. Women had an increased risk of developing mastitis if they reported nipple damage (IRR 2.17, 95 % CI 1.21, 3.91), over-supply of breast milk (IRR 2.60, 95 % CI 1.58, 4.29), nipple shield use (IRR 2.93, 95 % CI 1.72, 5.01) or expressing several times a day (IRR 1.64, 95 % CI 1.01, 2.68). The presence of S. aureus on the nipple (IRR 1.72, 95 % CI 1.04, 2.85) or in milk (IRR 1.78, 95 % CI 1.08, 2.92) also increased the risk of developing mastitis.
  
  
  CONCLUSIONS
  Nipple damage, over-supply of breast milk, use of nipple shields and the presence of S. aureus on the nipple or in breast milk increased the mastitis risk in our prospective cohort study sample. Reducing nipple damage may help reduce maternal breast infections.
authors.affiliation: Judith Lumley Centre (formerly Mother & Child Health Research), La Trobe University, Melbourne, VIC, 3000, Australia. m.cullinane@latrobe.edu.au.
authors.forename: Meabh
authors.initials: M
authors.lastname: Cullinane
authors.affiliation: Judith Lumley Centre (formerly Mother & Child Health Research), La Trobe University, Melbourne, VIC, 3000, Australia. l.amir@latrobe.edu.au.
authors.forename: Lisa H
authors.initials: LH
authors.lastname: Amir
authors.affiliation: Murdoch Childrens Research Institute, The Royal Children's Hospital, Parkville, VIC, 3052, Australia. susan.donath@mcri.edu.au.|University of Melbourne Department of Paediatrics, The Royal Children's Hospital, Parkville, VIC, 3052, Australia. susan.donath@mcri.edu.au.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Donath
authors.affiliation: Murdoch Childrens Research Institute, The Royal Children's Hospital, Parkville, VIC, 3052, Australia. suzanne.garland@thewomens.org.au.|Women's Centre for Infectious Diseases, Royal Women's Hospital, Parkville, VIC, 3052, Australia. suzanne.garland@thewomens.org.au.|University of Melbourne Department of Obstetrics and Gynaecology, The Royal Women's Hospital, Parkville, VIC, 3052, Australia. suzanne.garland@thewomens.org.au.
authors.forename: Suzanne M
authors.initials: SM
authors.lastname: Garland
authors.affiliation: Murdoch Childrens Research Institute, The Royal Children's Hospital, Parkville, VIC, 3052, Australia. sepehr.tabrizi@thewomens.org.au.|Women's Centre for Infectious Diseases, Royal Women's Hospital, Parkville, VIC, 3052, Australia. sepehr.tabrizi@thewomens.org.au.|University of Melbourne Department of Obstetrics and Gynaecology, The Royal Women's Hospital, Parkville, VIC, 3052, Australia. sepehr.tabrizi@thewomens.org.au.
authors.forename: Sepehr N
authors.initials: SN
authors.lastname: Tabrizi
authors.affiliation: School of Women's and Infants' Health, University of Western Australia, Crawley, WA, Australia. matthew.payne@uwa.edu.au.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Payne
authors.affiliation: Centre for Population Health Research, Deakin University, Burwood, VIC, 3125, Australia. catherine.bennett@deakin.edu.au.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Bennett
mesh_terms: D000293:Adolescent; D000328:Adult; D001942:Breast Feeding / Q000009:adverse effects*; D002176:Candida albicans / Q000302:isolation & purification*; D002177:Candidiasis / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008413:Mastitis / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology; D008875:Middle Aged; D049590:Postpartum Period; D011247:Pregnancy; D011446:Prospective Studies; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology; D013211:Staphylococcus aureus / Q000302:isolation & purification*; D011795:Surveys and Questionnaires; D014739:Victoria / Q000453:epidemiology; D055815:Young Adult