This post continues the “merdish” theme of the previous article. There are two of types of microbiology samples in this area which I have always had some reservations about as to their usefulness. These are samples from peri-anal abscesses and pilo-nidal sinuses.

There a few reasons why I believe that sampling from these areas are of (very) limited usefulness:

• Samples taken from areas this close to the anus will almost certainly be colonised with enteric flora (no matter how good toilet hygiene is!). Therefore it can be difficult to work out was is pathogenic and what is just there for the sake of it.
• For both these conditions, the treatment should be primarily surgical, and antibiotic treatment is very much a secondary option.
• If antibiotics are being used, given the nature and location of perianal abscesses and pilonidal sinuses, anaerobic cover is required. However due to the poor sensitivity of culturing anaerobes from microbiological samples, anaerobes may not necessarily be recovered from the microbiological sample. This should not however change the treatment. I.e Anaerobic cover should not be stopped just because the microbiology result shows “No anaerobes isolated.”

I suspect that the results of microbiology samples from peri-anal abscesses and pilo-nidal sinuses hardly ever changes the management of the patient and I certainly do not encourage such sampling.

I would be keen to know if any laboratory takes a harder line on such sampling and places a disclaimer comment or even rejects these types of sample.

Michael