Trichosporon spp.

Associated infections

• Invasive trichosporonosis and disseminated infection
• Fungaemia, frequently catheter-associated
• Pneumonia in immunocompromised hosts
• Urinary tract infection
• Endocarditis and prosthetic valve infection
• Peritonitis in peritoneal dialysis patients
• White piedra of the scalp, facial or pubic hair
• Summer-type hypersensitivity pneumonitis
• Cutaneous and soft tissue infection in the immunosuppressed
• Onychomycosis

Transmission route

Most invasive infections are thought to arise endogenously from prior gastrointestinal or cutaneous colonisation in a host whose defences have been compromised, with breach of barriers by central venous catheters, urinary catheters, mucositis or abdominal surgery providing the route of entry. Exogenous acquisition from the environment is also plausible given the genus's wide environmental distribution, and Trichosporon species have been recovered from hospital water, wet surfaces and moist equipment.

The balance between these routes is not firmly established, and in practice the two are difficult to separate, since a patient colonised from an environmental source and subsequently infected from their own skin presents identically to one infected from an endogenous gut reservoir. What is reasonably clear is that the genus tolerates moist environmental niches, adheres to and forms biofilm on polymeric surfaces, and has been reported from the same categories of wet point that support other environmental yeasts: sink areas, wet benches, humidified equipment and inadequately dried device channels. Catheter-associated fungaemia is the presentation most often reported, consistent with an organism whose principal environmental behaviour is colonisation of plastic in the presence of moisture.

With respect to reprocessing, Trichosporon has no established role as a primary water-system pathogen comparable to Legionella or the non-tuberculous mycobacteria, and it is not a recognised contaminant of well-controlled purified water loops. However, because the genus tolerates moist environmental niches and can adhere to and form biofilm on plastic surfaces, its recovery from an endoscope channel sample or from final rinse water should not be regarded as trivially environmental. The most likely explanations, in descending order of probability, are sampling or handling contamination, colonisation of a wet point-of-use fitting or hose downstream of water treatment, residual moisture in channels or storage cabinets following inadequate drying, or carry-over of patient-derived material through incomplete cleaning. Repeated isolation, particularly of the same species, warrants investigation of the drying and storage stages of the reprocessing cycle and of point-of-use water quality against the requirements of AS 5369:2023, alongside review of aseptic sampling technique.

Relevance in endoscopy and reprocessing

There is no substantial published record of Trichosporon-associated endoscopy outbreaks or pseudo-outbreaks comparable to the documented Rhodotorula bronchoscope episode, and that should be stated plainly rather than implied. The genus is not among the organisms for which endoscope reprocessing surveillance is primarily designed, and its recovery from a reprocessed device is uncommon. Its relevance is inferential, derived from behaviour it shares with other environmental yeasts rather than from a specific body of endoscopy incident literature.

That inferential relevance is nonetheless real. Trichosporon adheres to and forms biofilm on the polymeric materials used in endoscope channels, connectors and tubing, and it grows in the moist, low-nutrient conditions that follow an incompletely dried reprocessing cycle. As a vegetative yeast with no spore stage, it is inactivated by high-level disinfectants delivered at the specified concentration, temperature and contact time, and by thermal disinfection in a washer-disinfector; there is no evidence that it survives a correctly executed cycle. Where it appears on a reprocessed device, the explanation lies in the same places it does for other yeasts: retained bioburden shielding organisms from disinfectant contact, a shortfall in cycle parameters, contamination after disinfection, or growth in residual moisture during storage.

For CSD and dental water the position is similar. The organism is not a recognised coloniser of treated water loops, so a detection points to the wet tail of the system or to the handling environment rather than to the plant. In endoscopy specifically, a Trichosporon recovery should direct attention to channel drying verification, storage cabinet performance and the condition of flexible connectors and hoses. Because invasive trichosporonosis affects a narrowly defined and profoundly immunocompromised population, the immediate patient-risk implication of an environmental isolate is limited for a general endoscopy list, but it rises materially where the facility serves haematology, oncology or transplant patients, and the response should be scaled accordingly.

Interpreting a detection

A Trichosporon detection in a water or final-rinse sample sits between the clearly environmental organisms and the clearly human-associated ones. The genus is genuinely present in the natural and built environment, so a positive is not implausible on its face; but it is also a skin and gut coloniser and is not a recognised resident of treated water loops, so handling contamination remains the leading explanation for a single low-count isolate. The interpretation should not default to either extreme without the surrounding information.

The first checks are the standard ones, with two additions. Confirm the identification, ideally to species level, because a genus-level yeast report can conceal either a different organism entirely or a species with quite different implications, and because older biochemical platforms handle this genus poorly. Review the aseptic sampling record: who collected the sample, whether the outlet was disinfected and flushed, whether the container was handled correctly, and whether other samples in the same batch were positive. Then examine the wet tail of the system and the drying stage of the reprocessing cycle, since these are the two locations where a genuine environmental population would most plausibly establish. Confirm whether the sample was taken upstream or downstream of point-of-use filtration and whether filter change intervals are current.

A single isolate with a plausible handling explanation, no repeat and no clinical linkage is managed by correcting sampling practice and repeating the sample. Repeated isolation, particularly of the same species from the same outlet or device, indicates an established niche and shifts the investigation to physical remediation: hoses and flexible connectors, spray arms and seals, storage vessels, channel drying verification and storage cabinet air supply. Escalation to the facility infection-prevention service is warranted where detection is repeated, where counts are high, where the organism is recovered from both water and a reprocessed device, or where the facility serves haematology, oncology, transplant or intensive care populations in whom invasive trichosporonosis is a realistic risk. Any clinical isolate temporally linked to implicated equipment should be reported promptly, both because the environmental link is relevant to the investigation and because the intrinsic echinocandin resistance of this genus makes early correct identification clinically consequential.

Antimicrobial resistance

Trichosporon species are intrinsically resistant to the echinocandins, which do not effectively inhibit their cell wall synthesis, and are poorly susceptible to flucytosine. Amphotericin B frequently shows only fungistatic activity at achievable concentrations and clinical failures are well documented. The triazoles, and voriconazole in particular, are consequently regarded as the mainstay of therapy for invasive trichosporonosis. Acquired azole resistance is an emerging concern: fluconazole resistance in T. asahii has been reported from multiple regions, and reviewed mechanisms include point mutations in the ERG11 gene arising under continuous azole exposure and hyperactivity of efflux pump drug transporters. Voriconazole heteroresistance has also been described in clinical isolates.

Species-level identification and susceptibility testing are therefore important, since empirical echinocandin therapy directed at presumed candidaemia will be ineffective. This is one of the clearest examples in medical mycology of identification directly determining outcome: a patient with Trichosporon fungaemia started on an echinocandin for presumed candidaemia is receiving no effective therapy at all, and the delay until the organism is correctly identified is time during which a high-mortality infection progresses untreated. Removal of an implicated intravascular catheter is generally required in addition to antifungal therapy.

Antifungal resistance should not be conflated with disinfectant resistance, and the distinction is important when interpreting an environmental isolate. Trichosporon has no meaningful tolerance of the chemistries used in reprocessing. It is a vegetative organism inactivated by peracetic acid, glutaraldehyde and ortho-phthalaldehyde at label conditions, by thermal disinfection, and by chlorine at water-treatment concentrations. Its intrinsic echinocandin resistance is a property of its cell wall biology that has no bearing on its response to a high-level disinfectant. As with other environmental yeasts, the tolerance that matters operationally is biofilm-associated: cells embedded in matrix on the interior of a channel, hose or storage vessel resist short-contact chemical exposure, and durable control depends on eliminating residual moisture and stagnation rather than on intensifying disinfection.