Objective: To assess whether free-living and/or biofilm bacteria are present in the putative sterile middle ear cavity before insertion of the electrode array during cochlear implantation.
Design: Prospective study.
Setting: Tertiary academic hospital.
Patients: The study included 45 healthy children (with or without a history of otitis media) undergoing cochlear implantation.
Interventions: Transmission electron microscopy or scanning electron microscopy was used to detect the presence of bacteria.
Main outcome measure: Presence of both free-living bacteria and biofilm bacteria on the epithelial surface of biopsy specimens of middle ear mucosa.
Results: A majority of all mucosal specimens from clinically healthy tympanic cavities displayed inflammatory areas as well as dispersed, nonmatrix-enclosed bacteria. Also, rarely, fragments of biofilms were found.
Conclusions: The presence of bacteria in the tympanic cavity, which is generally assumed to be sterile in healthy individuals, may provide an explanation for infectious complications after cochlear implantation. However, the possibility that the electrode array of a cochlear implant will actually become contaminated during insertion is unlikely because of the small amounts and dispersed presence of bacteria, which may account for the relatively low incidence of infectious complications after cochlear implantation.