Background: In general practice, infectious conjunctivitis is a common and mostly (64%) self-limiting disorder. In case of aberrant course or severe symptoms a general practitioner may take a culture. Direct inoculation is considered the reference standard but usually a swab is sent to a laboratory.
Objectives: To compare the diagnostic performance of the swab, transported by surface mail with direct inoculation.
Methods: 19 General practitioners took two samples of the conjunctiva from 88 patients with symptoms suggestive of infectious conjunctivitis by rolling a cotton swab across the conjunctiva of the lower fornix. One swab was used to inoculate 3 agar plates directly, while the other was sent in a Stuart medium to the laboratory and inoculated at the time of arrival. We compared the number of positive cultures of both methods.
Results: A pathogen was found in 31 of 88 samples (35% (95%Confidence Interval:26 to 46)). Surprisingly, the number of positive cultures was higher for the Stuart medium (27/88), than for direct inoculation (23/88). The difference was 4,5%(90%CI:0 to 12, p=0.388; one-sided McNemar's test for paired proportions). In five of the 19 samples, that were positive in both tests the cultured pathogen were different.
Conclusions: We found that the Stuart medium detected more bacteria than direct inoculation. The lower 90%confidence bound, testing non-inferiority at p=.05 indicates that is is unlikely that the Stuart medium misses any positive cultures compared to direct inoculation.