Microbiology Profile of COVID-19-Associated Rhino-Orbital Mucormycosis Pathogens in South India

This study describes the microbiological and histopathological features of patients with COVID-19-associated rhino-orbital mucormycosis (ROM) seen at the L V Prasad Eye Institute between May and August 2021. Diagnosed clinically and radiologically, 24 patients with ROM were included in the study. Deep nasal swabs or endoscopically collected nasal swabs or orbital tissues were submitted for microbiological evaluation and in vitro susceptibility testing by microbroth dilution for natamycin, amphotericin B, caspofungin, posaconazole, ketoconazole, and voriconazole. Cultures were processed by 28S ribosomal DNA polymerase chain reaction and molecular sequencing. A portion of orbital tissues was also sent for histopathological evaluation. The age of the patients ranged from 27 to 75 (mean 48.58 ± 14.09) years and the majority (79%) were male. Nineteen patients were known to be diabetic prior to developing ROM and 18 patients had recovered from active COVID-19 infection. Thirteen patients had a history of hospitalization during COVID-19 infection and eight received steroids. Of the 24 samples, microbiological evaluation identified Rhizopus arrhizus in 12, Rhizopus microsporus in 9, Lichtheimia ramosa in 2, and Rhizopus delemar in 1. Twelve isolates were tested for antifungal susceptibility and all were susceptible to natamycin and amphotericin B. The susceptibility to posaconazole was high, with minimum inhibitory concentration (MIC) < 2 µg/mL for 10/12 (84%) isolates, whereas the MIC of other drugs varied. Histopathological examination of tissues showed acute fulminant disease, granuloma formation, and vascular invasion by the fungal pathogens in these specimens. Rhizopus arrhizus was predominantly associated with ROM and most isolates were susceptible to amphotericin B and posaconazole. Further studies are needed to corroborate the findings and explain possible underlying links.