The common causes of persistent ear discharge are chronic otitis media, chronic otitis externa, and infection in the cavities made by tympano-mastoidectomies and fenestration operations. It is difficult to assess the proportion of the population suffering from running ears, but Formby (1942) reported that just over 2% of recruits examined during the 1939-45 war were rejected because of chronic ear diseases. Otorrhoea formed the bulk of the cases. Johnston (1948) found that of 1,902 factory employees 3.3 % had suppurating middle ears, and Asherson (1950) states that 1 % of the school population of London in 1932 were treated for chronic otorrhoea.
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