Another person has died in an outbreak of extensively drug-resistant bacteria linked to contaminated eye drops, the Centers for Disease Control and Prevention reported in an update on Thursday.

The outbreak now totals 81 cases across 18 states. In addition to the four deaths, health officials have tallied reports of 14 people with vision loss and an additional four people who have had their eyeballs surgically removed (enucleation) due to infection.

The bacteria behind the outbreak is a strain of Pseudomonas aeruginosa dubbed VIM-GES-CRPA. This unwieldy acronym stands for a carbapenem-resistant P. aeruginosa (CRPA) with Verona integron-mediated metallo-β-lactamase (VIM) and Guiana extended-spectrum-β-lactamase (GES). It is an extensively drug-resistant strain of bacteria that, until this outbreak, had never been seen in the US before.

US health officials have traced the bacteria's origins to contaminated eye drops, with EzriCare artificial tears being the most common product used by people infected during the outbreak. The Food and Drug Administration reported a recall of these drops in February after the CDC released a health alert about 55 cases and the link to the eye drops. The manufacturer of EzriCare eye drops, India-based Global Pharma, also recalled two other products it makes: Delsam Pharma’s Artificial Tears and Delsam Pharma’s Artificial Ointment. The CDC and the FDA advise people to stop using these products immediately if they haven't already.

Before the recalls, the eye drops were readily available nationwide and sold through Amazon, Walmart, eBay, and other retailers. Clinical samples indicate the contamination spans from at least May 2022 to April 2023, though the CDC has advised health care professionals to report any suspect clinical samples dating back to January 2022.

This week's outbreak update includes 13 new cases since the last outbreak update in March, six of which had samples collected prior to the recall and are now confirmed and added to the tally. Of the seven other newly added cases, most either resided in long-term care facilities with other known cases or reported continued use of one of the recalled artificial tears, the CDC reported.

Public health threat

CDC officials previously told Ars that the outbreak strain is particularly concerning because it can spread quietly from person to person and share drug-resistance genes with other pathogens.

"To date, extensively drug-resistant Pseudomonas with genes that rapidly spread resistance, like VIM and GES, have been rare in this country," Marissa Grossman, a CDC epidemic intelligence service officer, told Ars. "The widespread introduction of the outbreak strain… threatens to undermine efforts to prevent these highly resistant organisms from becoming more common."

Based on bacterial isolates collected during the outbreak, the strain of P. aeruginosa is resistant to antibiotic drugs: cefepime, ceftazidime, piperacillin-tazobactam, aztreonam, carbapenems, ceftazidime-avibactam and ceftolozane-tazobactam, fluoroquinolones, polymyxins, amikacin, gentamicin, and tobramycin, the CDC reported. Based on three isolates that underwent antimicrobial susceptibility testing, the strain still appears susceptible to the drug cefiderocol. But the CDC advised doctors to work with specialists to determine treatment plans for the extensively drug-resistant pathogen.

The agency also highlighted that researchers at the University of California at San Diego’s Center for Innovative Phage Applications and Therapeutics (IPATH) and the Yale Center for Phage Biology and Therapy have identified bacteriophage with activity against the outbreak strain. Bacteriophage (or just phage) are viruses that selectively infect and destroy bacteria, and researchers have for decades explored ways to use them to treat bacterial infections. Interest in the therapy has increased as pathogenic bacteria have become more and more resistant to our largely stagnant collection of antibiotic drugs.

While doctors and researchers work to treat the tenacious infections, some patients have already filed lawsuits against EzriCare, Global Pharma, and retailers. The FDA posted an inspection report of Global Parma's facility, finding a slew of manufacturing violations, slime on equipment, and a lack of measures to ensure sterility.