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Infection hits US teaching labs

May 10, 2011 By Erika E Check Hayden This article courtesy of Nature News.

Wave of infections triggers investigation into biosafety practices.

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A spate of lab-associated Salmonella infections has swept across the United States during the past year, prompting public-health officials to examine how closely labs are following infection-prevention protocols.

"The fact that cases seem to be happening all over the country has raised the question of whether there are issues with laboratory safety and appropriate training techniques," says Mack Sewell, state epidemiologist at the New Mexico Department of Health in Santa Fe.

Between August 2010 and March this year, 73 infections due to Salmonella typhi­murium, a relatively common strain of the bacterium, caused illness in people across 35 states and one death, the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, reported on 28 April. The outbreak now seems to have ended, with the number of reported new infections dropping to the usual baseline of 0–4 per week, the CDC says.

The strain of Salmonella involved in the outbreak often causes food-borne illnesses and has been linked to past epidemics. But what sets this recent outbreak apart is that many of the illnesses have been traced back to clinical or teaching laboratories, according to the CDC report.

The agency conducted an in-depth investigation of 32 people made ill during the current outbreak, and found that 60% of them had had some connection with a microbiology laboratory in the week before their illness, compared with 2% of 64 people with other reported illnesses. The New Mexico Department of Health found that the outbreak strain was genetically identical to a commercially available strain used in some of the labs linked to ill workers or students. Furthermore, some victims of the illness reported working with Salmonella at the bench.

Laboratory-acquired infections are relatively common. One voluntary survey of 88 labs between 2002 and 2004 found that 33% had experienced at least one lab-acquired infection during that time, including six Salmonella infections (E. J. Baron and J. M. Miller Diagn. Microbiol. Infect. Dis. 60, 241–246; 2008). In 2008, the CDC convened a panel to look into the incidence of laboratory-acquired Salmonella infections; it has not yet released a report.

But it is unusual for lab-acquired infections to crop up across the country, and the CDC is investigating how this may have happened, in part by surveying the biosafety practices of members of the American Society for Micro­biology, based in Washington DC, and the Association of Public Health Laboratories in Silver Spring, Maryland.

The CDC is also concerned because some of those made ill in the outbreak, such as young children, had never visited a lab but lived with someone who worked in a lab and did not get sick. This suggests that the lab worker carried the pathogenic bacteria home on bags, clothes or other objects, says the CDC's Casey Barton Behravesh. And it raises the question of whether use of this pathogenic Salmonella strain in teaching labs is necessary.

"We are wondering whether there is a non-pathogenic or attenuated strain of Salmonella that could be used in place of this one," Barton Behravesh says.

For now, public-health officials are advising all lab workers to be more careful about observing proper biosafety procedures. Recalling a memorable lesson imparted by his own professor, Sewell suggests one way to cement the importance of those precautions: "He told us that anyone who catches something they're working with gets an automatic 'F'."

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