A decreasing trend in tinea cruris caused by Epidermophyton floccosum, an anthropophilic dermatophyte, has been observed.

This retrospective study involved Thai naval cadets aged 18 years or older with suspected groin lesions. Both clinical evaluations and laboratory investigations were conducted.

In total, 86 male participants with a median age of 19 years who presented with groin rash were enrolled in the study. Branching septate hyphae from KOH examination were found in 55 patients (64.0 %). Fungal identifications were Epidermophyton floccosum (42 cases; 76.4 %), Trichophyton mentagrophytes complex (3 cases; 5.5 %), and no growth (10 cases; 18.2 %). An E. floccosum outbreak was identified, with a prevalence of 76.4 %. Most lesions exhibited admixed erythema and hyperpigmentation. Approximately two-thirds displayed prominent, easily visible scaling. Scrotal involvement was absent in 95.2 % of lesions, with 87.2 % presenting bilaterally. A gradual symptom onset lasting up to 2 months was observed in 78.9 % of cases. Lesion morphologies included annular (73.8 %), patchy (14.3 %), and polycyclic (9.5 %). Severe itching disrupting daily activities was reported by only 7.1 % of participants. Approximately two-thirds used over-the-counter (OTC) topical medications without consulting a physician. Risk factors related to clothing included sharing clothes (59.5 %), wearing sweaty clothes (100 %), and reusing unwashed clothes (81.0 %).

The E. floccosum tinea cruris outbreak among naval cadets was characterized by a gradual onset and mild symptoms. OTC medication use without physician consultation was prevalent.