Molecular diagnosis of rhino-orbital mucormycosis in a COVID-19 setting

Mucormycosis is a severe fungal infection caused by species of the order Mucorales. Early and accurate diagnosis is a prerequisite in the management of the disease. In the present study, we evaluated and compared two PCR-based techniques for the diagnosis and identification of mucormycosis in patients with rhino-orbital mucormycosis (ROM) post-COVID-19.

Diagnosed clinically and radiologically, 25 patients of ROM were included in the study and endoscopically or blind collected nasal swabs or orbital tissues were submitted for microbiological evaluation (direct microscopy + culture) and PCR using primers targeting two different loci (ITS and 28S rDNA region) for diagnosis. All PCR products were further processed for species identification using Sanger sequencing whenever possible.

Of the 25 samples included in the study, 16 samples were positive for presence of fungal filaments by Smear suggestive of Mucorales sp., but only 7/25 grew in culture. ITS-based PCR was able to identify mucormycosis in 7/25 (28%) samples and 28S rDNA PCR showed positivity for 19/25 (76%) samples. Rhizopus oryzae was found to be the predominant species in our study. The sensitivity and specificity of 28S rDNA PCR compared to culture were found to be 85.71% and 27.78%, respectively, while for ITS-based PCR, they were 42.86% and 77.78%, respectively.

28S rDNA-based PCR is a reliable and sensitive method for early diagnosis of mucormycosis. Molecular techniques have shown a promising future to provide quick and effective treatment by accurately identifying the aetiologic agent.