I have never found ear swabs a very satisfactory microbiological sample, the outer ear canal usually being filled with all manner of debris and micro-organisms regardless of whether an infection is present or not. (Try processing a swab from your own ear!)

In addition it is often difficult to tell from the request form whether the swab has been taken from the external part of the ear or right inside the canal.

I doubt whether the results of many ear swabs ever affect the clinical outcome of the patient.

Nevertheless I have a few rules for ear swabs, to help both the scientists and myself make the results generated as sensible as possible.

• If respiratory organisms (H. influenzae, S.pneumoniae, M. catarrhalis) isolated from a toddler ear swab, it is likely to be an otitis media with a perforation. (there is also the possibility that the organism has got into the ear from the mouth via the finger of the toddler). I tend to do susceptibilities on such isolates on the rationale that a systemic antibiotic may be indicated for recalcitrant cases.
• If Staphylococcus aureus and Streptococcus pyogenes are isolated together from an “ear swab” then the chances are it is an impetiginous lesion. Therefore I do susceptibilities on the staphylococcus (but not the S. pyogenes, see “Excuses”)
• Rule of three. If three or more organisms are isolated from an ear swab then you are essentially wasting your time identifying every member of the zoo. What help is this going to be to the clinicians. Would simply report as “Mixed flora” or “Mixed Coliforms.”
• With the exception of the first two points above I would hardly ever perform susceptibilities on isolates from ear swabs. I am not aware of any evidence that doing this improves patient outcomes. The one exception to this would be where there is clinical details of “mastoiditis”. In this clinical scenario, if there is a pure or dominant organism, or a Pseudomonas aeruginosa, it should be worked up.

Ear swabs are over-worked, over processed and over-interpreted in clinical microbiology laboratories all over the world. 

The results of ear swabs can sometimes help with clarifying the aetiology of the ear symptoms, as described above. However they do little to affect the management of the patient, and we should bear this in mind when processing them…..

MIchael