Healthcare-associated fungal infections: beyond Candida and Aspergillus.
Neofytos et al report a case of infection with one these rare pathogens, Rhodotorula mucilaginosa. (7) Species of Rhodotorula most often isolated from humans include Rhodotorula mucilaginosa, R glutinis, and R minuta. Yeast members of the family Cryptococcaceae, Rhodotorula spp. have been increasingly reported to cause human disease. (8) Immunocompromised patients, especially those with central venous catheters and other indwelling devices, are at highest risk for infection. While Rhodotorula appear to be less virulent than the more common yeast pathogens such as Candida and Cryptococcus neoformans, Rhodotorula infections have been described to cause sepsis syndrome and other significant complications. (8-10) In addition, Rhodotorula are almost uniformly resistant in vitro to two of the most commonly used systemic antifungal agents, fluconazole and caspofungin. (11)
The case reported by Neofytos et al illustrates several challenges associated with the emergence of previously rare fungal pathogens. The first challenge relates to accurate diagnosis. Many clinical laboratories have only recently begun to provide species-level identification of Candida and Aspergillus isolates. The accurate identification of the stunning array of rare and emerging fungi pose an even greater challenge to the microbiologist. Every hospital providing care for immunocompromised patients should either have the ability to identify fungal organisms to the genus (and sometimes, species) level or should have a close relationship with a referral clinical mycology laboratory that can do so. For Rhodotorula, fortunately, the identification is made easier by virtue of the carotenoid pigments they produce, leading to the characteristic color of Rhodotorula colonies (salmon pink to coral red), and by their urease positivity. (12)
A second challenge posed by emerging fungi relates to the determination of their pathogenic roles. As the spectrum of fungal pathogens expands in an ever more immunocompromised patient population, fungi that were traditionally felt to be of low or no pathogenic potential are increasingly isolated in clinical cultures. (6) We should now recognize that almost any fungus can cause disease in a sufficiently immunocompromised host, making it unwise to dismiss the isolation of an unusual fungus as a contaminant. In the patient described by Neofytos et al, the organism appears to have been relatively avirulent, producing little by way of signs or symptoms of infection. Nonetheless, the repeated isolation of the organism from a normally sterile site (bloodstream) clearly established it as a pathogen, and case reports of Rhodotorula spp. causing clinical disease such as ocular infection, peritonitis, and meningitis provide reason enough to institute therapy.
A third challenge posed by emerging fungal pathogens is uncertainty regarding therapeutic options. Unlike Candida and Aspergillus, for which treatment guidelines are available and can be based upon randomized clinical trials data, little or no data exists to guide the therapy of less common fungi. In these circumstances, one must rely upon the combination of case reports, expert opinion, and any existing in vitro susceptibility data from surveillance programs. As reviewed by Neofytos et al, the available data for Rhodotorula infections suggests that the combination of device removal and amphotericin B is the most conservative therapeutic approach, with the possible addition of flucytosine (5FC) to amphotericin B for severe or refractory disease. While it is true that some Rhodotorula spp., including the isolate causing infection in this case, may have low minimum inhibitory concentrations (MICs) to voriconazole or posaconazole, other Rhodotorula may demonstrate high MICs, (11) and insufficient data are available to document efficacy or to suggest whether in vivo emergence of cross resistance is likely to occur among these inherently fluconazole-resistant organisms. Had this patient not been lost to follow-up, it would have been interesting to examine the in vitro susceptibility of any recrudescent Rhodotorula isolated after prolonged exposure to voriconazole.
Finally, this case should remind us of the importance of device removal when fungal infections involve devices. Had the patient allowed it, removal of the infected catheter would have greatly increased the likelihood of clearing the infection. In the absence of follow-up, it is not possible to determine whether failure to clear the organism was due to inadequate antifungal therapy, or to an inability to remove the infected device, or both.
In summary, Rhodotorula spp. are one among several opportunistic yeast-like fungi emerging as causes of infection in immunocompromised hosts (others include Saccharomyces cerevisiae, Trichosporon spp., and Geotrichum capitatum [Blastoschizomyces capitatus]). Given that Rhodotorula spp. are resistant to the two agents most commonly used to treat invasive candidiasis (fluconazole and caspofungin), it is important to recognize these infections so that appropriate therapy can be instituted. The increasing diversity of fungal pathogens will continue to pose considerable diagnostic and therapeutic challenges.
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I You gain strength, courage, and confidence by every experience in which you really stop to look fear in the face ... You must do the thing you cannot do. --Eleanor Roosevelt
Daniel J. Diekema, MD, FACP
From the Departments of Internal Medicine and Pathology, University of Iowa Carver College of Medicine, Iowa City, IA.
Reprint requests to Daniel J. Diekema, MD, FACP, Clinical Associate Professor, Departments of Internal Medicine and Pathology, University of Iowa Carver College of Medicine, 200 Hawkins Drive, Iowa City, IA 52242. Email: firstname.lastname@example.org
Accepted October 17, 2006.
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|Author:||Diekema, Daniel J.|
|Publication:||Southern Medical Journal|
|Date:||Feb 1, 2007|
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