Superficial fungal skin infections are among the most prevalent infectious diseases worldwide, estimated to affect approximately 20%–25% of the global population during their lifetime.^1,2 The most common cause of these conditions is dermatophyte fungi (e.g., Trichophyton, Epidermophyton, and Microsporum).^2,3 Tinea corporis (ringworm of the trunk, arms, or legs) and tinea cruris (jock itch) are common clinical presentations of dermatophytosis, characterized by pruritic, erythematous, annular skin lesions that can spread easily among humans and animals or by fomites.^3,4 While historically considered minor conditions, tinea corporis, and tinea cruris pose public health concerns due to their impact on quality of life, associated stigma, potential for large outbreaks in communal settings, substantial healthcare burden, and risk of bacterial superinfections in immunocompromised populations.^2,5,6 Public health concern is increasing due to emerging antifungal resistance, particularly with recalcitrant, extensive dermatophyte infections caused by Trichophyton indotineae spreading globally.^7,8

However, recent national baseline data on tinea corporis and tinea cruris incidence and risk factors are limited and could inform US public health efforts and clinical practice. National studies on these conditions are outdated or solely laboratory-based.^9–11 In this study, we analyzed incidence, risk factors, and treatments of tinea cruris and tinea corporis in a large US Medicaid-insured patient cohort.

We identified patients with ≥1 outpatient visit during July 1, 2016–June 30, 2023, in the Merative^™ MarketScan^® Multi-State Medicaid Database. We required patients to be continuously enrolled in health insurance from 180 days before to 365 days after their first outpatient visit. We ascertained tinea cruris and tinea corporis diagnoses, underlying conditions, diagnostic testing, and outpatient prescriptions using International Classification of Diseases, Tenth Revision (ICD-10) codes and Current Procedural Terminology codes (Supplementary Table). Underlying conditions included immunosuppressing conditions and atopy. Immunosuppressing conditions included HIV, immune-mediated inflammatory disease, diabetes, cancer, and solid organ transplant and hematopoietic stem cell transplant. Atopic conditions included allergic dermatitis, allergic rhinitis, food allergy, and asthma. To capture incident tinea corporis or tinea cruris diagnoses, we excluded patients with a diagnosis of the condition in the 180 days before or on their first outpatient visit. Patients were followed for 365 days to ascertain whether they received a diagnosis of tinea corporis or tinea cruris. We estimated incidence rates and assessed potential risk factors by calculating adjusted incident rate ratios (aIRR) using multivariable Poisson regression, controlling for age, sex, race/ethnicity, immunosuppressing conditions, and atopy. We described diagnosis and treatment practices.

Among ~6 800 000 enrollees, 54 108 received a tinea corporis diagnosis (incidence: 79.1/10 000 person-years, 95% confidence interval [CI]: 78.7–79.6). Incidence was highest among those who were aged <5 years (129.9, CI: 127.8–132.1) and Black (99.5, CI: 98.2–100.8) (Table 1). Overall, 8386 enrollees received a tinea cruris diagnosis (12.2, CI: 12.0–12.4). Incidence was highest among those who were aged 45–64 years (25.8, CI: 24.7–27.0), male (18.6, CI: 18.1–19.1), and unknown race/ethnicity (14.9, CI: 14.0–15.9) or White (12.7, CI: 12.3–13.1).

In multivariable analyses, factors associated with higher tinea corporis incidence included age <5 (aIRR: 3.1, CI: 3.0–3.2; referent: 18–44 years), female sex (1.1, CI: 1.1–1.1), Black race (1.3, CI: 1.3–1.4; referent: White), and having an immunocompromising (1.5, CI: 1.4–1.6) or atopic (1.6, CI: 1.5–1.6) condition. For tinea cruris, 45–64-year-olds had the highest aIRR (1.2, CI: 1.1–1.3) and those aged <5 years had the lowest (0.3, CI: 0.3–0.4). Female sex was associated with a lower incidence (0.3, CI: 0.3–0.3). Across racial/ethnic groups, aIRRs were generally similar. Immunocompromising (1.9, CI: 1.7–2.0) and atopic (1.7, CI: 1.6–1.8) conditions were associated with a higher incidence of tinea cruris.

Overall, <10% of patients received diagnostic testing (Table 2). Among patients diagnosed with tinea corporis, direct microscopy was the most common diagnostic test (42.4% of those receiving any diagnostic testing, 2.6% of patients with tinea corporis diagnoses overall). Among those diagnosed with tinea cruris, the most common diagnostic tests included direct microscopy (38.7% of those receiving diagnostic testing, 3.5% of patients with tinea cruris diagnoses overall) and susceptibility testing (39.6% of those receiving diagnostic testing, 3.6% of tinea cruris diagnoses overall). Most were prescribed antifungal therapy, 69.2% for tinea corporis (6.8% oral only, 55.9% topical only, and 6.4% both oral and topical) and 59.4% for tinea cruris (7.5% oral only, 45.6% topical only, 6.2% both oral and topical); 6.9% of tinea corporis and 10.1% of tinea cruris patients received a combination antifungal-corticosteroid product.

Tinea corporis primarily affected young children, Black patients, and those with atopic or immunocompromising conditions, whereas tinea cruris most commonly occurred in middle-aged men and was associated with immunocompromise and atopy but not race/ethnicity. Comparison with previous literature is limited by differing study designs; however, the age and sex differences observed between the tinea cruris and corporis cohorts are broadly similar to an analysis of a large commercial laboratory dataset.¹¹ The disproportionately high rates of tinea corporis among Black patients align with findings from a 1995–2004 cross-sectional study.¹⁰ This racial disparity is also observed with tinea capitis, with higher incidence among Black children compared with other racial groups.¹² Additional research is needed to investigate factors influencing differing infection rates across demographic groups and to support targeted public health interventions to address this disparity.

Treatments observed included antifungal-corticosteroid topical use, which is generally discouraged and has been linked to persistent or recurrent tinea corporis infections in children. While these combination creams may provide quick symptomatic relief, they lower clinical cure rates in the management of dermatophytosis and have been linked to persistent and recurrent tinea corporis infections.^13,14,15

A major study limitation was the lack of diagnostic testing in the majority of cases (>90%), and therefore misdiagnosis is possible. Diagnostic testing and laboratory confirmation are important to support accurate and prompt diagnosis, appropriate treatment, and antifungal stewardship efforts.¹⁶ These low testing rates may indicate challenges regarding Clinical Laboratory Improvement Amendements (CLIA) restrictions limiting potassium hydroxide and microscopy testing, limited patient encounter time, low reimbursement rates for diagnostic testing, lack of physician education on the importance of mycological testing, or lack of clinician confidence in their ability to perform or interpret direct microscopy testing. These challenges could be addressed through clinician education on appropriate diagnostic testing techniques and interpretation and incentivization of diagnostic testing for the purpose of improving patient care and antifungal utilization.

The dataset lacked information on disease severity and over-the-counter treatments, possibly underestimating antifungal use. Misdiagnosis could have occurred given infrequent testing. Nonetheless, we update benchmark data on tinea corporis and cruris and emphasize a continued need for diagnostic testing and judicious antifungal use in an era of emerging resistance.

Supplementary material are available at Medical Mycology online.