Rhinocerebral Mucormycosis in Sri Lanka - Aetiology and Antifungal Susceptibility

Introduction and objectives: Mucormycosis is a deadly fungal infection caused by Mucorales group of fungi. Amphotericin B (AMB) and posaconazole are the antifungal drugs recommended for treatment. However, susceptibility of Mucorales to those agents may vary. Main objective of this study was to describe the anti- fungal susceptibilities of clinically significant Mucorales in Sri Lanka.
Methodology: Retrospective cross-sectional study was performed with Mucorales isolated from sinonasal specimens received at the Mycology Reference Laboratory, Medical Research Institute, Sri Lanka from 2014 to 2021. Genus identification was done phenotypically and broth micro-dilution test was performed to test the susceptibility for AMB and posaconazole. Available clinical data were analysed.
Results: There were 158 isolates of Mucorales. Mean age of the patients was 56 years and 54% were females. Major associated factor was diabetes mellitus, followed by COVID-19 infection. Commonest pathogen was Rhizopus sp. in 154 (97.5%) patients. Ninety-three (92%) isolates were susceptible, five (4.9%) were intermediate and three (2.9%) were resistant to AMB.  Eighty-five isolates (84%) were susceptible, thirteen (12.9%) were intermediate and three (2.9%) were resistant to posaconazole. There was no significant difference in Minimum Inhibitory Concentrations (MIC) values between AMB and posaconazole (P = 0.4355) to Mucorales.
Discussion: Rhizopus sp. is the most common Mucorales that causes human infections worldwide and so in our country. Previous studies have shown that the most active antifungal agent against Mucorales was AMB followed by posaconazole. High mean MIC of posaconazole in Rhizopus sp. was also reported earlier. However, in the current study the MIC of posaconazole was not significantly different from that of AMB.
Conclusion: This study on clinical isolates of rhino-cerebral mucormycosis in Sri Lanka demonstrates that the commonest causative agent is Rhizopus sp. AMB and posaconazole are effective and they have comparable MIC on the Mucorales isolated from patients with rhino cerebral mucormycosis in Sri Lanka.