Why do we bother taking conjunctival swabs?
Is it for therapeutic reasons? The patient may expect this investigation. The clinician may be acting out of habit or seeking to reassure the patient that he is doing a professional job.
Is it to discriminate between bacterial and viral conjunctivitis? I think most clinicians can do this fairly well from examination for conjunctivitis. Besides, viral conjunctivitis is self-limiting (as is most bacterial conjunctivitis)
Is it to change management? The standard therapy for bacterial conjunctivitis in New Zealand and Australia is Chloramphenicol drops/ointment. It is a good broad spectrum antibiotic with excellent coverage against the normal pathogens of bacterial conjunctivitis. (Staph aureus, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis). Failure of this therapy is usually due to poor compliance, not given frequently enough, lack of associated eye cleansing, re-infection etc.. It is almost never due to lack of in-vitro susceptibility of the pathogen to the chloramphenicol. Low resistance rates are probably due to the fact that chloramphenicol is rarely used as asystemic antibiotic nowadays because of the risk of marrow aplasia.
In summary I think there are a whole heap of conjunctival swabs taken which frankly do not need to be.
For example if your laboratory receives on average of 12 conjunctival swabs a day costing approx $20 each to process. If 10 swabs are not appropriate then that is $200 a day times 365= $70,000 a year.
The cost of unnecessary testing is not insignificant….
I think the genuine indications for conjunctival swabbing are as follows:
- Immunocompromised patient.
- Clinical/epidemiological suspicion of gonorrheal or chlamydial conjunctivitis.
- Associated cellulitis of the skin around the eye.
- Condition not resolving after regular eye cleansing and empirical topical antibiotic therapy given at sufficient frequency and for sufficient duration.
It is time for the lab to stand up and say that these are the patients that we really want conjunctival swabs from, so we can focus our time, money and efforts, and make a genuine difference to the patient….