The deadly bacteria linked to recalled eyedrops causing infection and blindness had never been seen in the U.S. until 2022, according to the Centers for Disease Control and Prevention. It has since infected dozens and killed three people. Even though the contaminated bottles have been removed from stores and health care facilities, the CDC expects more cases to be identified.

What has infectious disease experts most alarmed is how this bug — a well-known type of bacteria, Pseudomonas aeruginosa — has evolved in a way that is resistant to nearly all available treatments.

As of April 7, the CDC had identified 68 cases of a new strain of Pseudomonas aeruginosa in 16 states. The investigation is still underway, although the agency has to wait for states to report other cases.

More than half of the cases have been found in long-term health care facilities. Nearly all are linked to contaminated eyedrops that had been imported from India.

Pseudomonas aeruginosa has been around for years. In 2020, there were an estimated 28,800 drug-resistant cases in hospitals in the United States, a CDC investigator not authorized to speak to the media said.

But the new infections revealed a form that had never before been reported in the U.S.: carbapenem-resistant Pseudomonas aeruginosa with Verona integron-mediated metallo-β-lactamase and Guiana extended-spectrum-β-lactamase.

The long name basically shows how its genes have transformed to make it more drug resistant over time.

"This was a Pseudomonas original," Dr. Robert Bonomo, a professor of medicine at Case Western Reserve University in Cleveland who has studied a variety of drug-resistant bacteria since 1990, said in an interview.

The CDC's investigation revealed that the infections linked to the eyedrops may only be treated by one known antibiotic, called cefiderocol.

There's nothing new about the way the mutated bacteria harms the body. It's the drug resistance that makes it so dangerous.

Eye infections have been most common. But because the eyes are directly linked to the nasal cavity, the bacteria can move into the respiratory tract and lead to pneumonia.

"Pseudomonas aeruginosa can affect pretty much any tissue in the body as travels through the blood, and it can cause sepsis," said Dr. Guillermo Amescua, a cornea specialist at the Bascom Palmer Eye Institute of the University of Miami Miller School of Medicine.

Amescua's team has treated seven patients affected by the outbreak.

The Connecticut Department of Public Health investigated its first case in June 2022. Since then, a department spokesman said, the agency has identified 26 patients. Most have been in long-term health care facilities.

Otherwise healthy people can spread the bacteria without ever knowing they carry the bacteria on their skin, although there is no evidence of person-to-person spread outside of health care facilities, the CDC expert said. Most cases have been linked directly to the contaminated eyedrops.

What eyedrops have been recalled?

EzriCare artificial tears was the brand most commonly reported among those who later became ill. Those drops have since been recalled, along with Delsam Pharma's Artificial Tears and its Artificial Eye Ointment.

Three patients have died. Eight needed corneal transplants. Four have had at least one eye removed.

The CDC first alerted the public to the potential danger surrounding the eyedrops in a statement on Jan. 20. But physicians across the country had been reporting cases of the new bacterial infections since at least last summer.

On Monday, the Food and Drug Administration released a preliminary report from an inspection at the Global Pharma Healthcare facility in India, finding problems with the manufacturing process and the factory's measures to assure sterility, according to reporting from The Associated Press.

Most of the infections were not caught until they were advanced.

This occurred in the case of Juan Lopez, 93, of Miami, Florida. He'd been using the now recalled EzriCare artificial tears for months before developing an eye infection in January. His doctor prescribed antibiotic eyedrops.

But by the beginning of February, Lopez developed a 103 degree fever and was hospitalized. Blood tests revealed drug-resistant Pseudomonas aeruginosa.

Lopez was successfully treated, and advises others to pay attention to unusual symptoms. "Don't delay. Definitely go get checked," he said.

The mutated strain of Pseudomonas underscores the growing risk of antibiotic resistance.

"These bacteria were on the planet way before we were, and over millions and millions of years, they've evolved mechanisms by which they can survive," said Bonomo, the Cleveland professor.

"We like to think we can keep up, but they have the propensity to be one step ahead," Bonomo said. "This puts us in a bad place."

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This article was originally published on NBCNews.com