Practice Rational Testing

Ordering and interpreting ear swabs in otitis externa

BMJ 2014; 349 doi: https://doi.org/10.1136/bmj.g5259 (Published 01 September 2014) Cite this as: BMJ 2014;349:g5259
  1. Carl Llor, senior visiting research fellow1,
  2. Cliodna A M McNulty, consultant microbiologist2,
  3. Christopher C Butler, professor of primary care13
  1. 1Institute of Primary Care and Public Health, School of Medicine, Cardiff University, Cardiff CF14 4XN, UK
  2. 2Public Health England Primary Care Unit, Microbiology Department, Gloucestershire Royal Hospital, Gloucester, UK
  3. 3Department of Primary Care Health Sciences, Oxford University, Oxford, UK
  1. Correspondence to: C Llor carles.llor{at}urv.cat

Learning points

  • Investigations are rarely useful in a first episode of uncomplicated otitis externa. Ear swabs are not recommended. First line empirical treatment includes topical 2% acetic acid, with antimicrobial eardrops, such as an aminoglycoside (if the tympanic membrane is intact), as second line. Aural toilet and analgesia may also be indicated

  • Consider swabbing the ear canal for culture to identify likely pathogens and susceptibilities in the following circumstances only:

    • The condition does not improve after initial empirical topical treatment

    • Otitis externa is recurrent or chronic

    • After ear surgery

    • Topical treatment cannot be delivered effectively

    • There is suspicion that the infection has extended beyond the external auditory canal

    • The condition is severe enough to require systemic antibiotic treatment

  • The most common infective causes of otitis externa are Pseudomonas aeruginosa and Staphylococcus aureus, both of which are covered by acetic acid or aminoglycoside drops

  • Avoid targeting antimicrobial treatment to common commensal organisms of the ear canal

  • Direct treatment of polymicrobial infections to those pathogens most likely to cause severe otitis externa (S aureus, Streptococcus pyogenes, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis)

An otherwise healthy 25 year old woman was initially treated by her general practitioner with a 10 day course of topical antibiotic and steroid eardrops for unilateral ear fullness and pain, which was diagnosed as otitis externa. She consults again seven days later because of ongoing ear pain, discharge, and reduced hearing, despite having used the ear drops as prescribed. She has not been feverish. On examination, her left pinna is tender and her ear canal is diffusely swollen and erythematous, with a grey exudate dotted with dark debris.

What is the next investigation?

This patient’s symptoms have not improved after initial treatment. Her GP still considers this to be otitis externa, so decides to prescribe an oral non-steroidal anti-inflammatory …

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