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Rhizopus microsporus Infections Associated with Surgical Procedures, Argentina, 2006-2014
Abstract:
Rhizopus spp. fungi are ubiquitous in the environment and a rare but substantial cause of infection in immunosuppressed persons and surgery patients. During 2005-2017, an abnormally high number of Rhizopus infections in surgery patients, with no apparent epidemiologic links, were reported in Argentina. To determine the likelihood of a common source of the cluster, we performed whole-genome sequencing on samples collected during 2006-2014. Most isolates were separated by >60 single-nucleotide polymorphisms, and we found no evidence for recombination or nonneutral mutation accumulation; these findings do not support common source or patient-to-patient transmission. Assembled genomes of most isolates were ≈25 Mbp, and multiple isolates had substantially larger assembled genomes (43-51 Mbp), indicative of infections with strain types that underwent genome expansion. Whole-genome sequencing has become an essential tool for studying epidemiology of fungal infections. Less discriminatory techniques may miss true relationships, possibly resulting in inappropriate attribution of point source.
Insights
Whole-genome sequencing revealed that unusual Rhizopus fungal infections in Argentinian surgery patients were not linked to a common source or person-to-person spread. Different fungal strain types, some with expanded genomes, were identified.
Area of Science:
- Medical Mycology
- Infectious Disease Epidemiology
- Genomics
Background:
- Rhizopus species fungi are common environmental organisms.
- They can cause rare but severe infections in immunocompromised individuals and surgery patients.
- An unexplained cluster of Rhizopus infections in surgery patients occurred in Argentina between 2005 and 2017.
Purpose of the Study:
- To investigate the potential for a common source or transmission route for the observed cluster of Rhizopus infections.
- To analyze the genetic relatedness of Rhizopus isolates from Argentinian surgery patients.
Main Methods:
- Whole-genome sequencing (WGS) was performed on Rhizopus samples collected from 2006 to 2014.
- Analysis focused on single-nucleotide polymorphism (SNP) counts, recombination, and mutation accumulation.
- Genome sizes of different isolates were compared.
Main Results:
- Most Rhizopus isolates showed significant genetic divergence (>60 SNPs), indicating distinct strains.
- No evidence of recombination or nonneutral mutation accumulation was found.
- While most genomes were approximately 25 Mbp, several isolates exhibited substantially larger genomes (43-51 Mbp), suggesting genome expansion in certain strains.
- Findings do not support a common source or patient-to-patient transmission.
Conclusions:
- Whole-genome sequencing is crucial for accurate fungal infection epidemiology.
- Less discriminatory methods might obscure true relationships, potentially leading to incorrect source attribution.
- The Argentinian cluster likely involved diverse, independently acquired Rhizopus strains, some with expanded genomes.
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