Every year, an estimated 23,000 Americans die from antibiotic-resistant superbugs – germs that evolve so quickly, existing treatment options can't eradicate them.

But it's not just deadly drug-resistant bacterial infections that are spreading. We also have to worry about drug-resistant fungal infections, too.

A deadly, drug-resistant fungus called Candida auris is spreading on a global scale and causing what the Centres for Disease Control and Prevention (CDC) calls "urgent threats."

In 2009, doctors first found C. auris in the ear discharge of a patient in Japan. Since then, the fungus has spread not just to the US, but also numerous other countries, including Colombia, India, and South Korea, according to the CDC.

The CDC reported the first seven cases of C. auris in the United States in August 2016. In May 2017, a total of 77 cases were reported in New York, New Jersey, Illinois, Indiana, Maryland, Massachusetts, and Oklahoma. After looking at people in contact with those first 77 cases, the CDC determined that the quick-spreading fungus had infected 45 more.

As of February 2019, there are 587 confirmed cases of C. auris in the United States alone.

People with weakened immune systems have a high risk for infection

Typically, C. auris affects people with weakened immune systems who are in the hospital or have severe illnesses, according to the CDC. In fact, C. auris outbreaks have been reported in hospitals and healthcare centres around the world.

In the UK, an intensive care unit had to shut down after they found 72 people there were infected with C. auris, and in Spain,a hospital found 372 patients had the fungus. Some 41 percent of the Spanish hospital patients affected died within 30 days of being diagnosed.

C. auris worries healthcare experts because it can't be contained with existing drug treatments. It even has the ability to survive on surfaces like walls and furniture for weeks on end, according to the CDC.

People who contract these drug-resistant diseases typically die soon after contracting them because of their untreatable nature.

Most fungal and bacterial infections can be stopped using drugs. But with drug-resistant fungi and bacteria, their genes evolve so quickly that the treatment meant to target them proves ineffective and allows the dangerous disease to spread.

Drug-resistant diseases are difficult to detect

To make matters worse, many people who carry drug-resistant diseases don't show any symptoms and spread them unknowingly. According to the CDC, 1 in 10 people the agency screened for superbugs carried a drug-resistant disease without knowing it.

More specifically, someone may not realise they have C. auris if they are also sick with another illness, the CDC wrote on its website.

Fever and chills that don't go away following drug treatment are common C. auris symptoms, but the only way to diagnose the fungus is through a lab test.

Some experts think our over-reliance on pesticides and drugs creates superbugs

Doctors and researchers are still unsure what causes drug-resistant diseases, but they do know there are different strains of C. auris in different parts of the world, causing them to believe the fungus didn't come from a single place, The New York Times reported.

Some experts think heavy use of pesticides and other antifungal treatments caused C. auris to pop up in a variety of locations around the same time. In 2013, researchers reported on another drug-resistant fungus called Aspergillus and observed that it existed in places where a pesticide that targeted that specific fungus was used.

As pesticides, antifungals, and antibiotics continue to be heavily used on crops and in livestock, it's possible that the fungi and bacteria they're targeting learn how to evolve to stay alive in spite of the treatments.

Until researchers are able to pinpoint the cause of these drug-resistant diseases, the CDC is urging people to use soap and hand sanitizer before and after touching any patients, and reporting cases to public health departments right away.

This article was originally published by Business Insider.

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