Candida albicans

Associated infections

• Candidaemia and disseminated candidiasis
• Catheter-related bloodstream infection
• Oropharyngeal and oesophageal candidiasis
• Vulvovaginal candidiasis
• Candiduria and urinary catheter colonisation
• Denture stomatitis and other oral device-associated infection
• Prosthetic device and prosthetic valve infection
• Peritonitis following gastrointestinal perforation or peritoneal dialysis
• Endophthalmitis and chorioretinitis complicating candidaemia
• Cutaneous and intertriginous candidiasis, including napkin dermatitis
• Onychomycosis and chronic paronychia

Transmission route

The dominant route to infection is endogenous: colonising yeast from the patient's own mucosal surfaces translocates or is introduced during instrumentation, surgery or vascular access. Exogenous acquisition occurs mainly by contact, and hands have been repeatedly implicated as the vehicle in healthcare transmission. C. albicans is not a classical water-system organism in the sense that Legionella and Pseudomonas aeruginosa are; it does not have a recognised reservoir in the biofilm of building water distribution networks and is not expected in a well-controlled reverse-osmosis or purified-water loop.

The practical consequence is that the transmission pathways worth controlling are human ones. Hand hygiene at the points where clean and dirty workflows meet, glove changes between handling contaminated and reprocessed devices, and physical separation of decontamination and packing areas do more to prevent yeast contamination of reprocessed equipment than any intervention applied at the water plant. Contamination is also readily introduced during sampling itself, since the sampler's hands, skin scale and respiratory droplets all carry the organism, and a sample taken without proper aseptic technique from an otherwise compliant outlet can produce a positive result that has nothing to do with the water.

For that reason, recovery of C. albicans from endoscope channel samples or from final rinse water in a reprocessing setting is best treated as an indicator of contamination introduced downstream of treatment rather than as evidence of a colonised water plant. Plausible explanations include handling contamination during aseptic sampling, contamination of sample containers or taps, carry-over of patient-derived material through inadequate cleaning, or ingress at a point-of-use fitting, hose or drying cabinet. Because the yeast forms biofilm readily on plastics and elastomers, persistence in accessory components such as connectors, tubing and storage cabinets cannot be discounted.

AS 5369:2023 sets the final rinse water quality requirements for washer-disinfectors and manual reprocessing in Australian facilities. A repeated detection should trigger investigation of sampling technique, point-of-use filtration and the integrity of the reprocessing workflow rather than being dismissed as a benign environmental find. The distinction is between a single isolate, which is most often traceable to handling, and a repeated or high-count detection, which points to an established niche somewhere in the wet path between the water outlet and the stored device.

Relevance in endoscopy and reprocessing

Candida albicans is a recognised, if secondary, finding in endoscope reprocessing surveillance. Flexible gastrointestinal endoscopes and bronchoscopes pass through mucosal surfaces on which the yeast is a normal resident, so patient-derived yeast enters the channels of virtually every scope used. The question is never whether the organism is introduced but whether the reprocessing cycle removes it. Where manual cleaning is thorough and high-level disinfection is delivered at the correct concentration, contact time and temperature, C. albicans is readily inactivated: it is a vegetative organism with no spore stage, and it is well within the claimed spectrum of the peracetic acid, glutaraldehyde and ortho-phthalaldehyde formulations in routine use. Its recovery from a reprocessed scope therefore points to a failure of process delivery rather than to intrinsic resistance.

The two failure modes most often responsible are inadequate manual cleaning and inadequate drying. Retained bioburden, particularly proteinaceous and lipid-rich material from the gastrointestinal tract, shields organisms from disinfectant contact and is the single most common precursor to a positive channel sample. Drying failure is the second: residual moisture in an elevator channel, an air-water channel or a poorly ventilated storage cabinet allows any surviving cells to resume growth and to establish biofilm on the channel lining. Once biofilm has formed, the standard disinfection cycle is no longer reliably curative, because the matrix and the persister subpopulation described in the biofilm literature blunt the effect of a fixed-duration chemical exposure. This is the mechanism by which an intermittent contaminant becomes a persistent one.

In central sterilising and dental settings the relevance is narrower but real. Dental unit waterlines and their point-of-use fittings are wet, low-flow and often warm, and although yeasts are not the dominant flora of these lines, they can be recovered where line disinfection is neglected. In CSD, the exposure is to final rinse water and to the wet surfaces of washer-disinfector chambers, spray arms and load carriers. Because thermal disinfection cycles readily kill vegetative yeast, a C. albicans recovery from a CSD rinse sample points either to contamination after the cycle, during transfer or sampling, or to a fitting downstream of the disinfection step.

Interpreting a detection

A Candida albicans detection in a water or final-rinse sample should first be assessed for plausibility. This is not a water-system organism, and the base rate of genuine water-loop colonisation is low. The most probable explanation for a single, low-count isolate is contamination introduced at the point of sampling: an ungloved hand on the sample port, a container opened prematurely, a swab or bottle set down on a bench, or a tap disinfected inadequately before collection. The second most probable explanation is contamination of a wet fitting at or immediately upstream of the outlet, which is a genuine finding but a localised one. Colonisation of the treated water loop itself sits well down the list of explanations and should not be the first assumption.

The practical first checks are therefore procedural rather than engineering. Review who collected the sample and against what written method, whether aseptic technique was documented, whether the outlet was flushed and disinfected as required, and whether other samples from the same run were also positive, which would suggest a batch or laboratory issue rather than a plant issue. Confirm the identification, since environmental yeasts are readily misassigned by biochemical panels and a report of C. albicans may on repeat prove to be a different species with different implications. Check whether the sampling point sits before or after any point-of-use filtration, and confirm that filter change intervals have been met.

A single isolate with no clinical linkage, no repeat detection and a plausible handling explanation is managed by correcting sampling practice and repeating the sample. A trend changes the interpretation entirely. Two or more detections from the same outlet or the same scope, detections at rising counts, or recovery of the same organism from both rinse water and a reprocessed device indicate an established niche and warrant investigation of the wet path: hoses, connectors, spray arms, storage vessels, drying cabinet air supply and channel drying performance. Escalation to the facility infection-prevention service and the water safety group is warranted where detection is repeated, where counts are high, where the finding is accompanied by other organisms suggesting a general biofilm problem, or where any patient with device-associated or post-procedural candidiasis can be linked in time to the implicated equipment. In that circumstance the affected device or outlet should be quarantined pending investigation rather than returned to service on the strength of a single clear repeat sample.

Antimicrobial resistance

C. albicans generally remains susceptible to fluconazole and to the echinocandins, and acquired resistance is considerably less common than in Candida glabrata (Nakaseomyces glabratus) or Candida krusei (Pichia kudriavzevii). Where resistance does emerge it is usually associated with prolonged azole exposure and involves ERG11 point mutations, upregulation of the ERG11 target, or overexpression of CDR and MDR efflux transporters. Echinocandin resistance is uncommon in this species and is mediated principally by mutations in the FKS1 hot-spot regions that alter the glucan synthase target; it is seen most often in patients with prolonged echinocandin exposure or a deep-seated focus such as an abscess or a colonised device.

Biofilm-associated cells display a distinct and clinically important phenotype of reduced antifungal susceptibility that is not captured by standard broth microdilution testing of planktonic cells, and no biofilm-specific antifungal agent is currently in routine clinical use. The practical consequence is that a susceptible-looking minimum inhibitory concentration on a laboratory report does not predict the response of yeast growing on a catheter, a prosthesis or the lumen of an inadequately dried channel, and source control remains the decisive intervention.

In the disinfection context the picture is more favourable. C. albicans is a vegetative organism with no spore form and is inactivated by the high-level disinfectants used in endoscope reprocessing, by thermal disinfection cycles in washer-disinfectors, and by chlorine at concentrations used in water treatment. It is markedly more susceptible to chemical disinfection than bacterial spores, non-tuberculous mycobacteria or Cryptosporidium oocysts, and it does not share the disinfectant tolerance that characterises Candidozyma auris. Where the organism survives a reprocessing cycle, the explanation is almost always shielding by retained soil or biofilm, or a shortfall in disinfectant concentration, contact time or temperature, rather than an intrinsic tolerance of the agent used.