(NEXSTAR) – A deadly fungus spreading in more than half of U.S. states is so concerning in part because of the way it has evolved to be resistant to both antimicrobial cleaning products and anti-fungal drugs, the Centers for Disease Control and Prevention recently warned.

The fungus, Candida auris or C. auris, has mainly spread in health care settings, like hospitals and nursing homes. Counterintuitively, because hospitals are disinfected so frequently, they can be the birthplace of bacteria or fungus that are resistant to cleaning products and to treatments.

“If you think about the amount of cleaning that we do in the hospital versus what you do at home, it’s significantly greater in a hospital setting. So every time we’re spraying Clorox … that just creates the opportunity for more resistance,” Melissa Nolan, an assistant professor of epidemiology and biostatistics at the University of South Carolina, told Nexstar. “Over time, those pathogens have been able to evolve and adapt to resistance.”

Similarly, Candida auris has also developed a resistance to common anti-fungal drugs, which makes it hard to treat.

Echinocandins are the class of drug most commonly used to treat Candida fungi. While that sometimes works against Candida auris strains, the CDC says reports of “pan-resistant cases” are increasing.

Patients being treated for a Candida auris infection need to be closely monitored for signs the infection is drug resistant. “This organism appears to develop resistance quickly,” the CDC tells health professionals in its treatment notes.

“There are a very limited number anti-fungal medications that still work, but these should be verified by an anti-fungal susceptibility test to limit the potential for continued antimicrobial resistance,” Nolan adds. “The concern is if we stop seeing these last remaining medications being effective — then, there will be no remaining medications to treat this disease.”

If an infection isn’t responding to echinocandins, doctors may try to mix types of anti-fungal drugs or up the dosage, according to Mount Sinai Hospital.

When drugs aren’t working, it’s up to the patient’s immune system to fight off the infection. Someone with a healthy immune system will have an easier time beating back Candida auris than someone who is immunocompromised.

Unfortunately, the pathogen is most likely to spread to people who have compromised immune systems because it often enters the body through invasive medical devices like catheters or PICC lines.

The CDC estimates that “based on information from a limited number of patients, 30–60% of people with C. auris infections have died. However, many of these people had other serious illnesses that also increased their risk of death.”