Emergence of Cryptococcus gattii— Pacific Northwest, 2004–2010

E DeBess, DVM; PR Cieslak, MD; N Marsden-Haug, MPH; M Goldoft, MD; R Wohrle, DVM; C Free; E Dykstra, PhD; RJ Nett, MD; T Chiller, MD; SR Lockhart, PhD; J Harris, PhD


Morbidity & Mortality Weekly Report. 2010;59(28):865-868. 

In This Article

Editorial Note

C. gattii is an emerging infection in the United States. C. gattii appears to differ from its sibling species, C. neoformans, both in its clinical aspects (e.g., less responsive to antifungal drugs and more likely to cause tumor-like lesions called cryptococcomas) and its ecologic niche.[2,8] In addition, whereas the primary risk factor for C. neoformans cryptococcosis is severe immunosuppression (e.g., from HIV infection), risk factors for C. gattii infection in the United States appear to include both immunocompromise and exposure to specific regions of environmental fungal colonization .[2,8] Many cases of C. gattii infection are likely not recognized because distinguishing between C. gattii and C. neoformans requires plating on differential media not routinely available in clinical microbiology laboratories; therefore, many cryptococcal infections are never speciated. In addition, cryptococcal infections generally are not notifiable diseases in the United States, although C. gattii is now reportable in one state, Washington, as a rare disease of public health importance.

Until 1999, most human C. gattii infections were reported from Australia and other tropical and subtropical regions, including parts of Africa, Asia, the Mediterranean, South America, and southern California.[8] Fungal spores are known to colonize the nasal cavity and spread to other body sites, causing meningitis, pneumonia, and the development of lung, brain, or muscle cryptococcomas.[8] The infection is not known to be transmitted among or within animal species. Although C. gattii had been isolated rarely from environmental sources and patients in the United States before 2004,[2] U.S. outbreaks had not been reported.

Because C. gattii typically has been regarded as tropical or subtropical in geographic distribution, its emergence in a temperate climate suggests that the pathogen might have adapted to a new climatic niche, or that climatic warming might have created an environment in which minimum threshold conditions for C. gattii spore survival and propagation are attained consistently.[1,2] Alternatively, the environmental conditions supportive of C. gattii might be broader than previously suspected, or earlier propagation might have been inhibited by low concentrations of pathogen in the environment. In addition, infections might have occurred in the Pacific Northwest before the recognized increase in human cases, but too rarely to attract attention. However, retrospective speciation of 49 cryptococcal isolates from the Pacific Northwest obtained from 1997 through 2003[7] and 31 isolates from Vancouver Island obtained from 1987 through 1998[9] revealed exclusively C. neoformans, suggesting that the recent increase in reports of C. gattii represent actual emergence of the species in the region and not just an increase in disease awareness and reporting.

Additional systematic surveillance is needed to track C. gattii infection, along with increased awareness of the infection among public health practitioners, physicians, and veterinarians. In 2010, for the first time, surveillance data for C. gattii were reported at the Council of State and Territorial Epidemiologists meeting. The C. gattii Public Health Working Group is continuing disease surveillance and planning to conduct speciation of banked isolates of Cryptococcus. Improved surveillance should enable better assessment of the incidence of the disease and also its clinical manifestation and course.

Physicians should consider C. gattii as a possible etiology of infection when treating patients (particularly those who are HIV negative) who have signs and symptoms of cryptococcal infection, and should ask patients about recent travel to the Pacific Northwest, British Columbia, or other C. gattii–endemic areas. Physicians, particularly in the Pacific Northwest, should report suspected C. gattii infections and submit clinical isolates to their state health departments when requested.


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