Factors associated with positive bacteriological cultures of chronic middle ear effusions

Pathogenic bacteria have been isolated from middle ear effusions in a number of studies. Our aim was to identify factors which predispose to patients having positive cultures. Over a 1-year period, prospective data were collected on patients admitted for myringotomy. Middle ear effusions were collected at the time of surgery using specially designed traps, and underwent microscopy and culture. Data on local weather parameters were obtained from the Meteorological Office in Edinburgh, UK and compared with the patterns of positive cultures. A higher proportion of cultures were positive in October, November and December and in February and May than in the other months of the years. We were not able to relate these variations to any of the meteorological data, with the possible exception of relative humidity, or to any other variable.