Rhizopus microsporus is one of the main causative agents of mucormycosis. These mycoses are mostly described as isolated cases involving uncontrolled diabetes mellitus or immunosuppressed patients. In this work we report a nosocomial outbreak of mucormycosis due to R. microsporum involving three young immunocompetent patients whom underwent arthroscopic anterior cruciate ligament reconstruction surgery in a seven-month time span.

During the outbreak period, a total of 32 surgeries of this type were performed in the clinic (mucormycosis prevalence of 9.375%). The three patients presented healthcare-associated Mucormycosis comprising the bone surrounding one of the fixation screws (femoral or tibial). In addition to these three strains, another three R. microsporus strains isolated in the medical center during the same period of time were included in the study. One of these fungi was isolated from a skin lesion of a kidney transplant patient while the other two strains were isolated from environmental sources. Classical, mass spectrometry-based (MALDI-TOFF) and molecular identification were performed. Genetic relatedness was established by Rep-PCR (RAPD variant) and by single-linkage cluster analysis mass spectra. Cluster analysis was performed by unweighed pair group method with arithmetic mean (UPGMA).

All the strains were identified as R. microsporum by the used phenotypic and genetic tools. Clinical strains fell into 2 different clusters separating the renal transplant recipient strain from the three strains isolated post ACLR surgery, which clustered together.

The established genetic/mass spectra relatedness between the three post-surgery isolates suggests that these cases may be considered a healthcare-associated mucormycosis outbreak.