ATLANTA - Cryptococcus gattii, a fungal pathogen previously found only in tropical and subtropical areas, is emerging as a serious infection in the Pacific Northwestern United States, according to the Centers for Disease Control and Prevention.

It has infected at least 60 people and 52 animals in Washington, Oregon, Idaho, and California, according to Julie R. Harris, Ph.D., a CDC epidemiologist. This is "one of the most interesting emerging infectious diseases in the United States today," she said.

In September 2009, the CDC and various organizations in the affected states began passive surveillance for human and veterinary cases in the Pacific Northwest to understand the extent of the pathogen’s spread and its epidemiology.

Twenty cases were identified in 2009, and she expects that even more cases will be identified this year.

Of the 39 patients on which researchers have data, 89% were hospitalized; 33% died of or with the C. gattii infection, she said. The mean age of infected patients is 52 years (range, 15-95 years); C. gattii appears to affect men and women equally. It's rarely a pediatric disease. Moreover, it appears to infect both immunocompetent and immunocompromised patients, most of whom were not infected with HIV.

The most common symptoms are cough, shortness of breath, headache, nausea and vomiting, fever, and weight loss. The patients developed pneumonia (57%), meningitis (44%), encephalitis (21%), and cryptococcomas in the lung (34%) and the brain (25%).

Emilio DeBess, D.M.V., of the Oregon Department of Human Services, noted that C. gattii spores appear to live in association with certain trees and the soil around those trees. Humans can become infected by inhalation of the airborne fungi. "As far as we know, there is no human-to-human or animal-to-human transmission," he said.

Before 1999, reports of infection were generally limited to tropical and subtropical areas and were most prevalent in Australia. In 1999, it was identified in Vancouver Island, British Columbia and then jumped to the mainland in 2004, and spread to the U.S. Pacific Northwest. Most cases are in Washington and Oregon, but reports of infection also have been identified in Idaho and California, Dr. DeBess said.

One explanation for the recent transmissions is that the spores are carried by trucks on the I-5 corridor, which stretches from British Columbia to San Diego. "There are a lot of theories out there. That's the one we are working with at this point," he said. "Marion County [Oregon] along the I-5 corridor is the Petri dish of C. gattii."

Then again, Dr. DeBess acknowledged that "it's hard to say" whether C. gattii is truly spreading or if more cases are being identified as a result of more intense surveillance.

C. gattii may be underdiagnosed and, as a result, the mortality rate may be inflated, he added. Both he and Dr. Harris noted the U.S. mortality rate is higher than that reported in British Columbia. He hopes to improve surveillance and promote awareness among physicians and veterinarians.

One of the clinical challenges, Dr. Harris noted, is that most labs cannot distinguish between Cryptococcus neoformans and C. gattii.

"We want all physicians to be aware that this is a new possible etiology of cryptococcal infections in the United States, and if infected with C. gattii, their patients might require prolonged therapy with antifungal drugs, or special procedures and follow-up that normally aren't warranted with C. neoformans infections," she said in an interview.

"Although most patients either live in or have visited the Pacific Northwest, we would encourage all physicians to keep Cryptococcus gattii in mind when they see an atypical patient with cryptococcal infection, as we don’t yet know the extent of the endemic area," she said.

Because C. neoformans is so much more common than C. gattii, at this point she is not suggesting submission and speciation of every Cryptococcus isolate. "However, for patients with suspected C. gattii infection, we encourage clinicians to report the cases to their states and submit isolates as requested for further speciation," she said.

Risk factors are poorly defined at this point, she added. "We know anecdotally that many patients live in or near wooded areas or have occupations that involve contact with soil or wood, but we don't have a good group with which to compare these types of exposures. We do plan to conduct a study on this in the near future."

Dr. DeBess and Dr. Harris reported that they had no conflicts.

Cryptococcus gattii Emerges in Pacific Northwest