This new study from the Toronto Humane Society compared fungal culture and PCR results before treatment in 132 cats (28 positive on fungal culture and 92 negative) and during treatment in 17 positive cats. Before treatment, the sensitivity of PCR was 100% and specificity was 88.5%. In other words, a negative result was extremely reliable but there were quite a few false positive results. This is consistent with the nature of PCR, which can detect really tiny amounts of fungus that may not be clinically relevant, or even dead organisms.
During treatment, PCR was unreliable in this study, with results remaining positive in 82% of cats at the first negative culture and 65% at the second negative culture. That means fungal culture still needs to be used to determine cure.
In this study, 61% of cats considered to be at high risk of having dermatophytosis were culture-negative. This is consistent with previous findings. The authors argue that the cost of PCR can justified in terms of reduced length of stay and reduced cost of treatment while waiting for culture results, and that PCR could be a valuable tool to increase life-saving capacity in animal shelters.
- Jacobson et al, Journal of Feline Medicine and Surgery 2017, online publication ahead of print: http://journals.sagepub.com/doi/full/10.1177/1098612X17695899