“Nightmare bacteria” with the power to resist most antibiotics are popping up across the U.S., but new, aggressive policies can help stop them from spreading, federal health officials said Tuesday.

A new program for testing suspect bacteria turned up unusual antibiotic-resistance genes 221 times in 2017, the Centers for Disease Control and Prevention reported. And 11 percent of people screened for these superbugs carried them, even though they had no symptoms, the CDC said.

“CDC’s study found several dangerous pathogens, hiding in plain sight, that can cause infections that are difficult or impossible to treat,” said the CDC’s Dr. Anne Schuchat. “While they are appearing all over the place, an aggressive approach can snuff them out.”

Antibiotic-resistant germs kill more than 23,000 Americans a year.

They evolve quickly, developing mutations that let them evade the effects of antibiotics. If they are not stopped fast, they spread. Worse, the antibiotic-resistant DNA can be carried in little cassettes of genetic material called plasmids that bacteria can slip in their entirety to one another and to other species of bacteria.

It’s already happened several times in the U.S. — and when one superbug gives new powers to a different superbug, the result can be an infection that is impossible to treat.

“Once antibiotic resistance spreads, it is harder to control—like a wildfire,” the CDC said in a statement.

The World Health Organization has labeled antibiotic resistance a “fundamental threat” to humanity.

The CDC tried out a new system aimed at quickly identifying these superbugs. They’ve helped staff up state health departments and labs to speedily test samples so that hospitals, clinics and other facilities can rapidly isolate patients infected with them.

“We were able to put 500 additional staff across the country to help with this,” Schuchat told NBC News.

CARRYING GERMS, WITHOUT ANY SYMPTOMS

The results were sobering. One in four of the samples sent in carried superbug genes, the CDC team reported. When the facilities involved looked further, they found 11 percent of seemingly unaffected people screened carried such germs without having any symptoms.

“This means the germ could have spread undetected in that health care facility,” the CDC said.

That is what has been happening for decades with all sorts of infections, from methicillin-resistant Staphylococcus aureus (MRSA) to killer Clostridium difficile infections.

Inappropriate overuse of antibiotics is and has been a major factor, said Dr. Lance Price, who directs the Antibiotic Resistance Action Center at George Washington University.

“Healthy people will carry these bugs without symptoms,” said Price, who was not involved in the CDC study. “We can spread them to susceptible people. We can become almost like a human mosquito, spreading these germs.”

Healthy people can unknowingly transmit the germs to a cancer patient, someone getting an organ transplant, a vulnerable newborn or a frail elderly person. That’s when an infection can take hold and kill.

“What the CDC is highlighting is the need, once you identify people carrying these bugs, to screen them and also their contacts to make sure they haven’t passed these bugs,” Price said.

The CDC tested for two of the best-known superbug germs: carbapenem-resistant Enterobacteriaceae or CRE, and carbapenem-resistant Pseudomonas aeruginosa (CRPA) bacteria.

They compared the new strategy to a more limited approach aimed at fighting another type of bacteria that resist antibiotics called extended-spectrum beta-lactamases (ESBLs). The more assertive approach worked better.

“We have seen that an aggressive strategy is needed and it works well,” Schuchat said.

The intensive approach is expensive and time-consuming. It calls for rapid identification of resistance, something that itself requires a specialized lab. Then the affected clinic, hospital or nursing home has to make an infection control assessment and test patients without symptoms who may carry and spread the germ.

“The strategy requires a coordinated response among health care facilities, labs, health departments and CDC through the Antibiotic Resistance Lab Network,” the CDC said.

“This is a very aggressive approach but containment of new resistance germs is really important,” Schuchat added. “Otherwise we could see these new nightmare bacteria become very common and essentially untreatable.”

Funding is key, said Dr. Paul Auwaerter, president of the Infectious Diseases Society of America.

“The efforts detailed in the Vital Signs report were made possible through new congressional funding in 2016 to combat antibiotic resistance,” Auwaerter said. “We urge Congress to sustain and to grow that investment so that further progress will prepare us to meet the future challenges of antibiotic resistance from a position of strength.”

Price said it is already difficult to get doctors, hospitals and clinics to implement other programs that work, which include regular hand washing and disinfection, as well as testing and the appropriate use of antibiotics.

“I am a fan of what they are proposing to do,” he said.

But it will do little to catch superbugs that are already spreading in communities.

“I think what we need to do is not always wait for somebody to get sick. We need an active surveillance system,” Price said.

Plus, doctors need to do the right thing when people do turn up sick.

“They should be getting a culture before they write a prescription for an antibiotic,” he said.

But doctors are not using the quick tests that already exist.

“We need point-of-care tests, so that people can get that answer while they still at the doctor. Until payers start paying for these tests, no one is going to develop them,” Price said.

In the meantime, doctors who want good ratings give patients what they demand: a prescription, even though antibiotics do not help viral infections and are helping drive the evolution of superbugs.

“Nobody is writing a five-star review for that doctor who is a really good steward of antibiotics,” Price said.