One vs two negative fungal cultures to confirm mycological cure in shelter cats treated for Microsporum canis dermatophytosis: a retrospective study.

Abstract

The aim of this study was to determine how often one negative fungal culture (FC) was indicative of mycological cure (MC) when compared with two negative consecutive FCs in cats treated for Microsporum canis dermatophytosis. In this retrospective study, weekly FC data from shelter cats treated for M canis dermatophytosis were reviewed. Complete records from 371 cats were reviewed. The first negative FC was indicative of MC in 335 (90.3%) cats. In this group, all cats were otherwise healthy and either had obvious lesions (n = 237) or no lesions or evidence of resolving lesions (n = 98). In the 36 cats in which the first negative culture was not indicative of MC, there were two clinical subgroups. The first consisted of healthy but lesional cats (n = 19) that had one negative FC within the first 3 weeks of treatment followed by one or more positive FCs. The most likely explanation was sampling error. These cats went on to cure and the next negative FC was indicative of MC. In the second clinical group, cats were lesional but had concurrent medical problems (n = 17). These cats showed an initial good response to treatment (lesion resolution and an initial negative FC). However, this negative FC was followed by at least one strongly positive FC (>10 colony-forming units/plate) before proceeding to cure. These cats took the longest time to cure (mean 11 weeks; range 8-28 weeks). MC occurred after resolution of the concurrent health issues. There was very good agreement between using one negative FC vs two negative FCs for the determination of MC in healthy cats (kappa = 0.903). In cats where there has been high compliance with environmental cleaning, as well as topical and systemic treatment recommendations, two consecutive negative FCs may not be necessary to determine MC. The first negative FC in an otherwise healthy cat is likely indicative of MC. Good sampling technique is needed to avoid false-negative FC results.