Centers for Disease Control and Prevention

Yersinia pestis, the bacteria responsible for the plague, caused the death of a renowned vaccine researcher in 2009, raising fears about laboratory-acquired infections. Though rare, they can be devastating, prompting health experts to remind lab workers of the importance of following protocols.

The death of a University of Chicago scientist who contracted plague while working in his lab is a reminder of the rare –- but real –- risks to researchers who work with potentially dangerous bugs, a new review of the fatality  finds.

An estimated 500,000 workers are employed in laboratories in the United States, where they’re routinely exposed to a range of bacteria, viruses, molds and other infectious agents. No one knows how many get sick each year, mostly because there’s no systematic reporting of laboratory-acquired infections, health experts say.

In the last several months, however, federal health officials have investigated an outbreak of salmonella infections tied to dozens of microbiology students and workers across the country -- and, in several cases, their children and other family members -- who fell ill from a lab bug likely spread by contaminated cell phones, car keys and other personal items.

And now the latest issue of the New England Journal of Medicine updates the case of Malcolm Casadaban, 60, a professor of molecular genetics, who died in September 2009 after falling ill following experiments using a weakened strain of the Yersinia pestis bacteria that cause plague.  It was the first time a lab worker had contracted plague in 50 years and the first reported death tied to a lab, according to the Centers for Disease Control and Prevention.

In both situations, investigators said that said lack of attention to lab protocols might have contributed to the illnesses. Failure to consistently wear gloves when required, or bringing personal items like car keys and MP3 players into the lab environment raises the risk that infections move beyond the petri dish -- and into people.

University of Chicago Medical Center

Malcolm Casadaban, a University of Chicago professor, died in 2009 after working with the plague bacteria in his lab.

“It’s not the lab strain, it’s bad practice,” said Dr. Karen Frank, an assistant professor in the department of pathology at the University of Chicago and author of the latest research letter.

In Casadaban’s case, investigators also concluded that the vaccine researcher had a genetic condition that made him particularly susceptible to infection from the bacteria. He suffered from undetected hemochromatosis, a condition in which too much iron builds up in the body. The plague bacteria had been engineered to be safer by removing some of the germ's iron, but the scientist’s condition added it back.

“He had extra iron, which allowed this organism to make him sicker,” said Frank. It’s not clear how Casadaban was infected, but investigators suspect it was transmitted through contact with skin or mucous membranes.

Casadaban wasn’t identified by name in the NEJM letter or in a previous CDC report, but news accounts at the time and a university obituary indicate he was the respected lab worker who died after an infection.

Such incidents raise public fears of lab bugs escaping to infect the general population, but those fears are unwarranted, Frank said.

“There’s less risk coming from lab workers than from all the people visiting patients in the hospital,” Frank said.

In both of the cases in question, the lab strains of bacteria were found to be as safe as expected, she said. She characterized the level of lab workers’ personal worry about infections as “almost none.”

“As long as you’re doing what you’re supposed to be doing, you should be fine,” she said.

Follow msnbc.com health reporter on Twitter @jonel_aleccia.

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