# A Prospective Cohort Study Comparing Microscopy and Culture in the Diagnosis of Superficial Fungal Skin Infections

## TL;DR

This study compares microscopy and culture for diagnosing fungal skin infections, finding that using both improves accuracy, especially when symptoms persist despite initial testing.

## Contribution

The study provides evidence for a stepwise diagnostic approach using microscopy followed by culture when needed.

## Key findings

- Microscopy identified 25.0% positive cases, while culture detected 16.7%.
- Moderate agreement (κ = 0.487) was found between the two diagnostic methods.
- Trichophyton rubrum and T. mentagrophytes were the most commonly cultured organisms.

## Abstract

Superficial fungal skin infections are common but often misdiagnosed, which may result in inappropriate treatment and the worsening of symptoms. An accurate and timely diagnosis is essential to differentiate these infections from similar conditions such as secondary syphilis, annular psoriasis, and pityriasis rosea. This single-centre prospective cohort study at the National Skin Centre, Singapore, evaluated the diagnostic agreement between direct microscopy and fungal culture. Between August and December 2022, 268 skin scrape samples were collected from 149 patients with suspected fungal infections. Microscopy identified 67 (25.0%) positives, while fungal culture detected 42 (16.7%) positives. Among the 252 samples tested with both methods, 213 (84.5%) showed concordant results (κ = 0.487, p < 0.0001), a finding that indicates moderate agreement. The most commonly cultured organisms were Trichophyton rubrum and T. mentagrophytes. Our findings suggest that both microscopy and fungal culture may be performed to prevent true-positive cases from being missed. However, in cases where cost is a concern, microscopy can be selected as an initial diagnostic tool. Should microscopy be negative in cases with high clinical suspicion for fungal infection or when empirical treatment fails, culture remains a valuable follow-up test. These findings support a stepwise diagnostic approach—using microscopy first, then followed by culture when necessary—to improve diagnostic accuracy while enabling timely treatment.