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

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%.