Dual quantitative PCR assays for the rapid detection of Trichophyton indotineae from clinical samples.

Trichophyton indotineae is an emerging species of the Trichophyton mentagrophytes complex (TMC), responsible for an epidemic of widespread hairless skin infections that is frequently (50-70%) resistant to terbinafine. In order to initiate appropriate treatment as quickly as possible without waiting for culture positivity (10-15 days) and molecular identification from the strain, we developed a dual quantitative PCR (qPCR) for the direct detection of T. indotineae in clinical samples. We first designed a T. indotineae specific qPCR assay (TI-qPCR) targeting a single specific polymorphism in the internal transcribed spacer region. Although none of the 94 non-dermatophyte and 7 dermatophyte species were amplified, this TI-qPCR allowed amplification of other TMC species at a lower yield. With equal amounts (0.1 ng) of DNA per reaction, the mean quantitative cycle (Cq) values for T. indotineae and non-indotineae TMC were 27.9 (±0.1) and 38.9 (±0.3), respectively. Therefore, we normalised this assay against a previously validated pan-dermatophyte qPCR assay (PD-qPCR) and relied on the ΔCq [(TI-qPCR) - (PD-qPCR)] to identify T. indotineae versus other TMC species. Dual assay was validated using 86 clinical samples of culture-confirmed T. indotinea and 19 non-indotineae TMC cases. The mean ΔCq for non-indotineae TMC was 9.6 ± 2.7, whereas the ΔCq for T. indotinea was -1.46 ± 2.1 (p < 0.001). Setting the ΔCq at 4.5 as a cut-off value resulted in 100% specificity for the detection of T. indotineae. This dual qPCR assay quickly detects T. indotineae from skin scrapings, aiding in early diagnosis and treatment for patients with suspected infection.

Identifying the emerging species Trichophyton indotineae is long and requires to wait for culture positivity. We developed a dual qPCR strategy to detect T. indotineae directly from clinical sample with a 100% sensitivity.

Emergence of Difficult-to-Treat Tinea Corporis Caused by Trichophyton mentagrophytes Complex Isolates, Paris, France.

We describe 7 cases of extensive tinea corporis since 2018 in a hospital in Paris, France, after failure to cure with terbinafine. Molecular analysis indicated Trichophyton mentagrophytes internal transcribed spacer type VIII (T. indotineae). This strain, which has mutations in the squalene epoxidase gene, is spreading on the Indian subcontinent.

Continuous increase of Trichophyton tonsurans as a cause of tinea capitis in the urban area of Paris, France: a 5-year-long study.

Tinea capitis (TC) is a highly contagious fungal infection of the scalp due to dermatophytes in children. To obtain information on the epidemiology of TC in the urban area of Paris, we analysed the microbiological results of 3090 patients seen with suspected TC from October 2010 to September 2015 at Saint Louis hospital, Paris, France. A peak of TC was observed in 3-6 year-old children, followed by a progressive decrease until 16 years of age. Of the 1311 positive cultures, 95% (1246) yielded one of the three anthropophilic species [Trichophyton tonsurans (33.5%), Trichophyton soudanense (38.3%), or Microsporum audouinii (28.2%)]. When considering one TC case per family, we observed a significant increase of T. tonsurans (P = .018) during these 5 years. The increase was more pronounced (P = .0047) in patients of West-African descent (n = 666), and was at the expense of M. audouinii and T. soudanense. On the other hand, the Caribbean patients (n = 85) remained predominantly (72.9%) infected by T. tonsurans. Our results show a better virulence of T. tonsurans over other species as already reported. Since T. tonsurans has not been reported in Africa, the infection of patients of West-African descent probably took place in the Paris area by exchanges with Caribbean patients. This increase of TC due to T. tonsurans was observed in the context of griseofulvin being the only licensed paediatric treatment for TC in France, which should deserve reappraisal because terbinafine may be more efficacious.