Potentially Lethal Cryptococcus gattii Infection Emerging in Pacific Northwest

Emma Hitt, PhD

July 15, 2010

July 15, 2010 (Atlanta, Georgia) — At least 60 people in the Pacific Northwest have been infected with a potentially lethal emerging infection involving Cryptococcus gattii, according to the Centers for Disease Control and Prevention (CDC).

Julie R. Harris, PhD, MPH, a staff epidemiologist with the CDC, and colleagues from the Oregon State Public Health Laboratory, in Portland, and the Washington State Department of Health, in Tumwater, reported the findings here at the International Conference on Emerging Infectious Diseases 2010.

According to the researchers, the number of reports of cryptococcosis caused by C gattii, a fungal pathogen previously found only in tropical and subtropical areas, has increased in the Pacific Northwestern United States since 2004.

Cryptococcosis Reported in Humans and Animals

Of the 60 reports in humans in the United States, most have been in Oregon. A total of 52 cases have also been reported in animals, predominantly in cats and dogs, but also in dolphins, horses, birds, goats, and sheep.

According to Dr. Harris, it is unclear why there is an increase in C gattii in the Pacific Northwest, and in British Columbia. "There are several possibilities, including increased 'seeding' of the pathogen through increases in global trade and travel, new genetic combinations that permit adaptation to different environments, and climate change that supports pathogen colonization and infection in the area," Dr. Harris told Medscape Medical News.

The most common presenting symptoms are cough, dyspnea, headache, nausea/vomiting, fever, and weight loss. Clinical findings have been documented as pneumonia (57%), meningitis (44%), encephalitis (21%), cryptococcomas in the lung (34%), and cryptococcomas in the brain (25%).

Cryptococcosis Fatal in Up to One Third of Infected Patients

Of the 60 patients, 89% were hospitalized, and approximately one fourth to one third of patients have died directly as a result of C gattii infection. The mean age of infected patients is 52.4 years (range, 15 to 95 years), and both men and women appear to be equally affected.

"We are likely to see continued cases of C gattii in the United States, but it is hard to say where the spread will stop," Dr. Harris said. "We do not know what the specific requirements are for C gattii growth yet. We are working to answer this question."

According to Dr. Harris, clinicians should be considering C gattii in their differential diagnoses when they see a patient in the Pacific Northwest, or someone who has traveled to the Pacific Northwest in the previous year with symptoms consistent with the disease. "Clinicians should also consider a diagnosis of C gattii in any HIV-uninfected patient who is positive for cryptococcal antigen," she said.

Speciation of Infection Warranted for Diagnosis

The typical diagnostic test for Cryptococcus species cannot distinguish between the more common Cryptococcus neoformans and C gattii, so a clinician seeing an atypical patient with Cryptococcus should seek out speciation of infection. "This is particularly important, because symptoms and course of disease with C gattii are not the same as with C neoformans," Dr. Harris said. "C gattii causes more cryptococcomas, which are tumor-like fungal growths in the brain, lungs, and other tissues, and is slower to respond to antifungal treatment" than C neoformans.

According to independent commentator, John R. Perfect, MD, C gattii and C neoformans are similar in terms of diagnosis and prognosis. "Much of the outcome depends on the host and the need to identify the infection early," he told Medscape Medical News. "Both of these species cause cryptococcosis but have somewhat different ecological niches," he said.

Dr. Perfect is professor of medicine and acting chief, Division Infectious Diseases, at Duke University Medical Center, in Durham, North Carolina.

Findings in Pacific Northwest Need Context

He added, however, that these findings in the Northwest United States and in Canada need to be put in context. "There remains a major outbreak of cryptococcosis, with an estimated 1 million cases per year and 700,000 deaths, the vast majority of [which are] in sub-Saharan Africa and associated with pandemic HIV infection," he said.

According to Dr. Perfect, clinicians should refer to the 2010 Infectious Diseases Society of America cryptococcal guidelines for evidenced-based diagnosis and treatment recommendations (Clin Infect Dis. 2010;50:291-322).

The authors and commentator have disclosed no relevant financial relationships.

International Conference on Emerging Infectious Diseases (ICEID) 2010: Slide session M. Presented July 13, 2010.