(CNN) The number of cases of an emerging and often multidrug-resistant fungus in the United States has grown from seven to 122 over the past nine months, according to a field report in the Morbidity and Mortality Weekly Report issued Thursday by the US Centers for Disease Control and Prevention.

The fungus, Candida auris , can cause severe illness with high mortality, especially among high-risk patients, including those in intensive care units, those with a central venous catheter and those who have received antibiotics or antifungal medications.

"It seems to affect the sickest of the sick patients, particularly those in hospitals and nursing homes with other medical problems," said Sharon Tsay, lead author and an Epidemic Intelligence Service officer at the CDC.

A total of 77 US clinical (in hospitals) cases of C. auris were reported in seven states. After the patients' close contacts were screened, an additional 45 cases were identified, resulting in 122 US patients with the fungal infection as of May 12. Among the 77 clinical cases, the patients' average age was 70, and more than half, 55%, were men.

None of the infections reported in the US was resistant to all available antifungals, Tsay said.

Paige Armstrong, an Epidemic Intelligence Service officer for the CDC, said the multidrug-resistant fungus has been causing outbreaks in health care facilities worldwide.

"This is a fungus that's acting a lot like some super bacteria that we've seen previously," she said.

'Very concerning'

The CDC issued its first alert in June of last year , telling US hospitals to be aware of this fungus based on reports of spreading infections in health care facilities around the world.

The clinical cases, all identified through cultures taken as part of routine patient care, occurred in New York (53 cases), New Jersey (16), Illinois (four) and one each in Indiana, Maryland, Massachusetts and Oklahoma.

The patients who were identified by screening because they were contacts of the initial cases, though colonized with the fungus, do not show any symptoms of an infection. Most of these people were patients on the same ward in health care facilities.

"Most cases of C. auris that have been reported have been from the blood," Tsay wrote in an email, though she noted that it has also been seen in urine, the respiratory tract, wounds, bile fluid and the ear.

"The fact that it has been found in other sites may also reflect its ability to persist on a patient's body and be spread in the environment around them -- one of (the) reasons that C. auris is causing outbreaks," Tsay said.

First identified in Japan in 2009, C. auris has now been named as the cause of reported infections in more than a dozen countries. In August, the CDC described the first seven cases of infection in the US, most dating to the previous year and one in 2013.

Some strains of C. auris are resistant to all three major classes of antifungal drugs. But most cases that have been seen in the US have been treatable with antifungal drugs.

Armstrong recently investigated an outbreak in Colombia, working with health authorities there to learn more about how C. auris spreads.

The fact that this fungus is showing resistance to the existing three classes of antifungal drugs, "leaving no medication to treat" patients, is "obviously very concerning," Armstrong said. Multidrug resistance has not been seen in other species of Candida.

"The fact that it's causing outbreaks in hospitals and other health care settings (is) something we typically don't see with fungus," Armstrong said.

Another concern is that testing of patients' rooms identified C. auris on mattresses, beds, windowsills, chairs, infusion pumps and countertops. This ability to linger on the surfaces of health care environments and spread between patients is unlike most of the other 20 species of Candida that cause infections in humans.

Invasive infections

"Typically, fungus and particularly candida species are commensal organisms or organisms that live within us, that live within our guts," Armstrong said.

Infections can occur due to overgrowth, known as candidiasis. If it develops in the mouth or throat, it is called thrush. If it develops in the vagina, it is commonly referred to as a yeast infection. And if the Candida species enters the bloodstream and spreads through the body, this is an invasive candidiasis.

It is possible, though not likely, for an invasive infection to occur at times of surgery, prolonged hospitalization, an ICU stay or while taking a high number of antibiotics, Armstrong said.

"With C. auris, we're actually seeing this happen," she said, and not only among high-risk people.

"We're also seeing it in some patients that don't always fit all those characteristics, and then additionally, we're seeing it spread from person to person or the environment to people, and that's kind of the impetus for the reason why it's causing these outbreaks."

"The reason this is happening, the reason it's causing outbreaks, is because it's colonizing the skin at levels we don't typically see with most other species of Candida," Armstrong said.

Nicole Kirgan, a spokeswoman for the New Jersey Department of Health, said it is tracking cases throughout the state, performing ongoing investigations at some health care facilities, while working with the CDC and remaining "in close correspondence" with New York state.

"Risk factors include recent surgery, diabetes, broad-spectrum antibiotic and antifungal use (broad-spectrum means they protect against a wide variety of bacteria or fungus), and central venous catheter use," Kirgan wrote in an email.

"Infections have been found in patients of all ages, from pre-term infants to the elderly," she said. "The majority of patients identified with C. auris infections have had weakened immune systems."

Cases in New York have been concentrated among hospital patients and nursing home residents in the New York City area, with a single patient in Rochester who'd been treated in a New York City facility, according to a statewide health advisory issued May 5 by New York State Health Commissioner Dr. Howard Zucker.

Among New York state's 71 total cases -- 53 clinical cases, with an additional 18 screening cases -- 20 deaths have occurred as of May 5. Since all the patients had serious underlying medical conditions, it is difficult to attribute any deaths specifically to C. auris.

"It is important for New Yorkers to understand C. auris poses no risk to the general public," Zucker said. "C. auris is an opportunistic infection which primarily impacts patients who are already ill for other reasons."

Origins and prevention

Armstrong said that "whether or not it started in one place and spread to other countries" is of interest to the CDC, which used whole genome sequencing to determine the origins of the fungus causing infections in US patients. Based on the gene data, CDC scientists say, the fungus didn't "look like it started in one place and moved around."

"There are four different families or groups that emerged simultaneously ... and independently," Armstrong said.

Fungus samples in each state were highly related, the new CDC report indicates. All the New York cases, with one exception (plus a related screening case), came from the same genetic group as samples from South Asia. Though distinct from samples in New York, the New Jersey fungal infections were also related to those found in South Asia. Illinois cases showed a relationship to those found in South America.

"Resistance has also varied within those groups. We don't think it's necessarily spreading around the world, so to speak, but at the same time, when it does emerge somewhere, there's obviously concern that it will spread within the health care facilities or person to person," Armstrong said.

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Prevention is often a matter of good infection control and standard precautions , including good hand washing and hygiene, and personal protective equipment.

After a thorough cleaning with a sodium hypochlorite-based disinfectant, the fungus could not be found in the rooms of patients infected with C. auris.

"C. auris is still relatively rare in the United States and CDC is working hard to contain its spread," said Tsay, who noted that most people are at low risk of getting infected. "One of the best ways to prevent the spread of germs like C. auris in healthcare settings is good hand hygiene."