A mysterious death of a woman in Russia following a lab accident has stoked fears about plague spreading. But the odds of that actually happening remain very low, with the US Centers for Disease Control and Prevention saying on X Tuesday afternoon that the circumstances of the case remain unconfirmed and that there is “no indication of a broader threat to the United States” at this time.

“We are working across the US government to assess developments as additional information becomes available,” the agency said. “CDC and our interagency partners are prepared and will continue to monitor the situation closely.”

Last week, a young researcher died from severe pneumonia of “unknown” origin after reportedly breaking a test tube at her workplace, the Irkutsk Anti-Plague Institute in Siberia. The hospital that treated her before her death was placed under quarantine, and her coworkers at the lab were isolated, according to Radio Free Europe/Radio Liberty.

Christian Lindmeier, a spokesperson for the World Health Organization, told reporters in Geneva on Tuesday that the group has been in touch with Russian authorities. Based on currently available information, WHO says the ​public health risk to the general population is very low.

“I think that’s the correct assessment,” says Gigi Gronvall, an immunologist and senior scholar at the Johns Hopkins Center for Health Security. “We don’t know anything about anything right now.”

Russian authorities have said contact tracing hasn’t yielded any signs of dangerous pathogens spreading, according to the Associated Press. Infamous for causing millions of deaths in Europe during the Middle Ages, plague is rare today. It is caused by the bacteria Yersinia pestis, which is found in wild rodents and their fleas in many parts of the world. It’s spread to humans through the bite of an infected flea and occasionally through direct contact with an infected animal. Antibiotics can cure plague, but they must be started as soon as an infection is suspected.

Pneumonic plague occurs when a person inhales infectious droplets that contain the bacteria. In July 2025, an Arizona man died from pneumonic plague after exposure to infected cats. It can also spread from person to person through respiratory droplets during close contact. But human-to-human transmission is rare, with the last reported occurrence happening in 1924 in Los Angeles. The possibility, though, is why the CDC says it’s important to rapidly identify cases and treat them.

“Once you know that somebody has been exposed to it, and even if you have a doubt that somebody has been exposed to it, you can immediately start antibiotics to prevent the person getting afflicted with the disease and to avoid the continuous spread of the disease,” says Rutul Dalal, an infectious disease physician at Penn State Health St. Joseph Medical Center.