Molecular Identification of Etiological Agents in Fungal and Bacterial Skin Infections: United States, 2020–2024

<b>Background/Objectives</b>: Cutaneous infections of fungal and bacterial origins are common. An accurate diagnosis-especially concerning pathogens that are difficult to isolate on culture-can be achieved using molecular methods (PCR) with a short turnaround time. <b>Methods</b>: We reviewed records of skin specimens (superficial scrapings) submitted by dermatologists across the United States with a clinically suspected dermatitis. As per physician's order, specimens were tested for infections either fungal (N = 4262) or bacterial (N = 1707) in origin. All unique specimens (one per patient) were subjected to real-time PCR assays where cases suspected of a fungal etiology were tested for dermatophytes, <i>Malassezia</i> and <i>Candida</i>, and cases suspected of a bacterial etiology were tested for <i>Streptococcus pyogenes</i>, <i>Staphylococcus aureus</i>, and the <i>mecA</i> gene potentially conferring β-lactam resistance. <b>Results</b>: Fungal agents were detected in 32.8% (SD: 4.5) of the submitted specimens, with most attributed to dermatophytes (19.3% (SD: 4.9)), followed by <i>Malassezia</i> (8.7% (SD: 2.8)) and <i>Candida</i> (2.9% (SD: 1.0)). Dermatophyte detection was more common in the elderly (≥65 years) compared to young adults (18-44 years) (OR: 1.8 (95% CI: 1.5, 2.2)), whereas <i>Malassezia</i> was more commonly detected in younger age groups (12.1-13.6%) than the elderly (5.6%). <i>Candida</i> was more frequently observed in females while dermatophytes and <i>Malassezia</i> were more frequently observed in males. Approximately one quarter of the submitted skin specimens tested positive for <i>S. aureus</i> (23.6% (SD: 3.4)), of which 34.4% (SD: 9.8) exhibited concurrent detection of the <i>mecA</i> gene. An <i>S. aureus</i> detection was more frequently observed in males (OR: 1.5 (95% CI: 1.2, 1.9)) and in children (OR: 1.7 (95% CI: 1.2, 2.5)). <i>Streptococcus pyogenes</i> was rarely detected. Among specimens positive for dermatophytes, 12.0% (20/166) showed co-detection of <i>S. aureus</i> and <i>mecA</i>, which is in contrast to 6.8% (70/1023) detected in samples without a fungal co-detection and 6.2% (8/130) in samples positive for <i>Malassezia</i>. <b>Conclusions</b>: PCR testing, when available, can be valuable as a part of routine care for diagnosing patients with clinically suspected skin infections. Further studies are warranted to survey the prevalence of resistant <i>S. aureus</i> isolates in dermatology outpatients, in particular with regard to the association with dermatophyte infections.