Evaluation of the value of staining hair samples with a modified Wright-Giemsa stain and/or showing illustrated guidelines for the microscopic diagnosis of dermatophytosis in cats.

Background: Direct examination of the hair is a simple diagnostic test for the diagnosis of dermatophytosis; training is needed to use this test.
Hypothesis/objectives: To evaluate whether use of modified Wright-Giemsa blue stain and/or photographic images of infected and uninfected hairs improved the user's ability to identify infected or uninfected hairs.
Animals: Ten cats with, and 10 cats without, dermatophytosis due to Microsporum canis (n = 20).
Materials and Methods: Twenty unstained and 20 stained hair samples from each group (n = 40) were anonymized and examined by veterinarians using a light microscope. Participants recorded samples as "infected" or "uninfected". Participants were then shown and allowed to use photographic images while examining the same 40 samples.
Results: Without staining, investigators correctly identified 12.7 ± 4 of the 20 samples (mean ± SD) and with staining 13.6 (±3). After illustrative guidelines were shown, they correctly identified a mean of 16.9 (±2.5) unstained slides and 15.8 (±2.3) stained slides. "Illustrated guidelines" and "hair infection" significantly increased the probability of a correct answer, whereas "staining" did not. Logistic regression determined that "study participant", "illustrated guidelines" (OR = 2.6) and "hair infection" (OR = 2.1) had a significant influence on the results, whereas "staining" did not. Sensitivity and specificity of direct examination were 70.5% and 56%, respectively, compared with culture status.
Conclusions and Clinical Importance: When examining hairs for the presence or absence of infected dermatophyte hairs, diagnostic accuracy was improved when observers used illustrated guides compared with just examining stained slides.
(© 2018 ESVD and ACVD.)