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The Rise of Resistant Ringworm: Genomic Sequencing Confirms the First Two Reported U.S. Cases of Trichophyton Indotineae

Emerging Fungal Species Sparks Concern Among Healthcare Providers

The United States has officially reported its first two cases of Trichophyton indotineae (T. indotineae), a highly contagious and often antimicrobial-resistant fungus causing severe ringworm infections. These cases, detected in March 2023, have set off alarm bells among healthcare providers and scientists, as T. indotineae had been previously confined to South Asia. The breakthrough came through specialized genomic sequencing at the New York state public health laboratory, the Wadsworth Center.

Not Your Usual Ringworm

Dr. Avrom Caplan, a dermatologist at the NYU Grossman School of Medicine, first encountered T. indotineae when he saw a patient in January 2023 with a ringworm infection unlike the typical cases he had treated before. Unlike the common small, red, circular rashes associated with ringworm, this patient displayed a severe, widespread, inflamed, scaly infection that covered their thighs and trunk. The patient’s infection had begun during a trip to Bangladesh the previous summer, and several family members also developed similar infections. Despite multiple treatments, including first-line antifungal medication, the condition persisted upon their return to the United States.

This unusual case prompted Dr. Caplan to investigate further. He found evidence pointing to T. indotineae, which had not previously been reported in the United States. Additionally, his residents recalled a similar case from December 2021, suggesting the possibility of community transmission within the U.S. Dr. Caplan, following CDC advisories and connecting with experts in India, initiated specialized genomic sequencing to confirm the presence of T. indotineae.

Novel Genomic Sequencing Confirms an Emerging Threat

The highly specialized genomic sequencing conducted at New York’s Wadsworth Center distinguished T. indotineae from closely related species, such as Trichophyton mentagrophytes. The two fungi are indistinguishable through standard laboratory testing. Dr. Caplan’s efforts resulted in the confirmation of T. indotineae, marking the first U.S. cases of this alarming pathogen.

Next Steps and Concerns

Since March 2023, Dr. Caplan has identified around ten patients with confirmed or possible T. indotineae infections across the United States, many of whom had recently traveled to the Indian Subcontinent. Concerns persist that there may be more undiagnosed or misdiagnosed cases, leading to continued suffering and ineffective treatments.

Dr. Caplan underscored the need to enhance laboratory capacity for detecting and monitoring emerging antimicrobial-resistant ringworm, a crucial step in addressing this growing concern. The CDC is actively exploring options to provide broader support for this testing.

Informing Healthcare Providers

To raise awareness and ensure prompt diagnosis and treatment, Dr. Caplan emphasized the importance of educating healthcare providers and patients about T. indotineae. He advised that patients with widespread rashes should be referred to dermatologists, particularly if over-the-counter or prescription antifungal treatments have failed. A recent publication in CDC’s Morbidity and Mortality Weekly Report (MMWR) has helped bring national attention to this emerging infection, and Dr. Caplan has called for increased vigilance and communication among healthcare providers.

Healthcare professionals and dermatologists suspecting a T. indotineae infection should reach out to their local health departments, which can in turn contact the CDC for testing assistance via This proactive approach is crucial in managing the potential spread of this emerging health threat.

Source: Centers for Disease Control and Prevention

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