title: Re-examination of old truths: replication of a study to measure the incidence of lactational mastitis in breastfeeding women.
abstract: BACKGROUND
  The reported incidence of lactational mastitis varies greatly; the single highest reported incidence in the scientific literature is 33%. The purpose of this study was to collect data regarding incidence and experiences of lactational mastitis from women attending a meeting of lactation specialists and to compare findings in a similar population reported in 1990 by Riordan and Nichols.
  
  
  METHODS
  A retrospective questionnaire study was carried out with a group of Danish lactation specialists in 2011. The questionnaire was constructed to replicate that used in 1990 and included questions about occurrence of mastitis, the infant's age, breast segments afflicted, examination by a physician, use of antibiotics and possible causes of the illness.
  
  
  RESULTS
  As in the earlier research, respondents in this study reported a 33% occurrence of lactational mastitis. This cannot however, be considered as the incidence of mastitis. In order to state the incidence it is necessary to impose a time limit for the collection of data and to know the size of the population at risk. Incomplete emptying of the breast was the factor most frequently cited as the cause of mastitis.
  
  
  CONCLUSIONS
  Researchers must strive to be as exact as possible when reporting definitions and incidences of mastitis and should attempt to identify the true population at risk - in this case, all women who were breastfeeding in the uptake area under study, during a specified time limit. Well-designed studies in different global locations are needed before any conclusions can been drawn about the range of incidences of mastitis.
authors.affiliation: Department of Health Sciences, Lund University, Sweden, Helsingborg Hospital, Helsingborg, Sweden. linda.kvist@med.lu.se.
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Kvist