Antifungal Susceptibility Testing Experience in the Management of Culture-Positive Mucormycosis: Observation from a Large Healthcare System.

Background

Mucormycosis, an invasive fungal infection with high morbidity and mortality rates, requires prompt surgical and antifungal therapies; however, the role of antifungal susceptibility testing (AFST) in clinical management of mucormycosis remains underexplored. We aimed to describe the experience of using AFST in the clinical management of mucormycosis.

Methods

We conducted a retrospective study from 1 October 2017 to 8 February 2023. We included non-pregnant patients aged ≥ 18 years old with a positive culture for Mucorales and with proven or probable mucormycosis. We collected clinical and microbiological data using a chart review.

Results

Over the study period, a total of 119 patients were included, with 36 (30%) undergoing AFST. Of all patients, the median age was 54 years, with 80 (67%) being White and not Hispanic and 73 (61%) being male. Fifty-three (45%) patients had DM, 27 (23%) had hematological malignancy, 15 (13%) had SOT, and 23 (19%) had COVID-19. Half of the cases met the criteria of proven invasive mucormycosis, with pulmonary involvement being the most common presentation (46, 39%), followed by rhino-cerebral-orbital involvement (35, 29%). The majority of Mucorales isolates were Rhizopus species (79, 66%). Among the 36 who underwent AFST, posaconazole minimal inhibitory concentrations (MICs) were lower than isavuconazole (range 0.03 to 2 µg/mL versus 0.1 to 16 µg/mL, respectively). AFST resulted in a change in antifungal therapy from isavuconazole to posaconazole in 3/36 (8%) cases. There was no statistically significant difference in the mortality between the patients whose isolates received AFST versus those who did not have AFST performed.

Conclusions

AFST led to a change in antifungal therapy in a minority of mucormycosis cases. Further studies to understand the epidemiological range of antifungal MICs and the effect of AFST-informed antifungal therapy are needed.