A Comparison Between Potassium Hydroxide (KOH) Microscopy and Culture for the Detection of Post-COVID-19 Rhino-Orbital-Cerebral Mucormycosis

Abstract

Background and objective Mucormycosis is an emerging and serious angioinvasive infection caused by filamentous fungi related to the order of Mucorales and the class of Mucormycetes. There was a marked increase in the number of cases of mucormycosis in India following the second wave of the coronavirus disease 2019 (COVID-19) pandemic in the year 2021. In this study, we aimed to compare potassium hydroxide (KOH) microscopy with culture for the detection of post-COVID-19 rhino-orbital-cerebral mucormycosis (ROCM). Materials and methods The KOH microscopy was performed with a 10% or 20% KOH-mounted slide with specimens collected from suspected cases of post-COVID-19 ROCM. Simultaneously, the culture was done on Sabouraud dextrose agar (SDA). These were incubated at 37 ℃ and 25 ℃ for 28 days. Diagnostic parameters were calculated by comparing KOH with gold standard culture. Results KOH mount was positive for broad aseptate fungal hyphae in 322 (54.1%) cases, while it was negative in 244 (41.0%) cases. KOH mount was positive for other fungi in 29 (4.8%) samples. The diagnostic accuracy of the KOH mount for Mucorales was 70.3%. KOH mount had a sensitivity of 84.9%, specificity of 61.5%, positive predictive value (PPV) of 56.9%, and negative predictive value (NPV) of 87.2%. Conclusions Based on our findings, the KOH microscopy positivity rate was higher in tissue samples compared to nasal swabs, with a sensitivity of 84.9%, specificity of 61.5%, PPV of 56.9%, and NPV of 87.2%. The overall diagnostic accuracy of the KOH mount for Mucorales was 70.3%.