Between August 2010 and June 2011, the U.S. Centers for Disease Control and Prevention (CDC) counted 109 people in 38 states infected with a commercial strain of Salmonella Typhimurium most commonly found in microbiology laboratories. On Tuesday, the CDC released its final report on the outbreak, which Food Safety News first reported on in April 2011.

The outbreak, which hospitalized 13 individuals and resulted in one death, is notable because of its association with educational and clinical labs instead of food. Sixty percent of the ill reported being in or near microbiological labs in the week before their illness began, compared with two percent of respondents in the CDC investigation’s control group.

The number of ill also included several children living in the same household as someone who worked or studied in a microbiology laboratory, further suggesting that the infections came from neglectful exposure within a lab setting: Individuals likely improperly handled bacteria samples, which they then transferred to themselves or others.

In August 2011, microbiologist and eFoodAlert author Phyllis Entis criticized the labs involved linked to the outbreak, calling on teachers and lab managers to better prepare students and staff to safely handle harmful pathogens.

“My whole take is that there’s been poor training and poor attention to safe, sensible handling in the labs. It’s totally unconscionable,” Entis told Food Safety News Wednesday.

“I think people get careless,” she added. “The mindset is that these are strains meant to be control cultures for teaching or testing, so they must be relatively innocuous. The whole culture of protecting the individual gets lost in the shuffle.”

The CDC report did not identify the specific strain, referring to it only as “strain X,” though the outbreak’s prevalence and even distribution across the country suggests a common commercial source. Educational and clinical labs can purchase bacterial samples from a variety of distributors.

In December 2010, the New Mexico Department of Health first suggested a link between the infections and laboratories when three people — one student and two children of students — became infected with the commercial strain. The students involved were each studying microbiology at two separate community colleges.

Working with state and local health departments and public health organizations, the CDC conducted a survey in May 2011 to determine where staff from outbreak-related labs differed in their safety practices from those in labs not associated with the outbreak. While most standard lab practices appeared to be upheld across the board, the staff in outbreak-related labs had less knowledge of safety training materials and were less likely to train students on the symptoms of Salmonella infection during their safety training.

Regardless of universal rules against food in labs, the Salmonella bacteria could have transferred onto any number of objects brought into labs, including cell phones, pencils or textbooks. The CDC included safety advice for students and laboratory managers at the end of its report, emphasizing handwashing and thorough safety training.

Entis expressed concern that clinical labs were linked to the outbreak, saying that professionals working in a lab setting should be held to a high standard of safety.

“I could see how things could get out of control in educational labs, but that’s still no excuse for it,” she said. “For it to get out of control in a clinical lab is beyond the pale and absolutely unacceptable.”

When asked if similar lab-related infections might occur regularly without receiving national attention, Entis said it was difficult to say, but that carelessness in labs is a continual problem when students might not understand the risks of contamination. She also noted that there were no peaks in the infection graph, meaning the illnesses occurred evenly during the 11-month outbreak window — an indication of a perpetual problem.

Entis said that the ultimate take-away from this investigation was that microbiology teachers and lab managers need to make safety training a priority.

“I hope that the various people involved have learned their lessons in terms of taking sanitation and training seriously,” she said. “We need to remember to treat these lab cultures with the respect that they deserve.”


CDC Outbreak Map