Laboratory surveillance stops spread of foodborne outbreaks

Surveillance and tracking systems are not the sole propriety of crime fighters. They have their place in the public health laboratory system, too, where they are put to work fighting the spread of illness.

The Hygienic Laboratory is part of a public health surveillance network that includes physicians, epidemiologists, laboratorians and IT professionals who collect, analyze and transmit data about the incidence of reportable illnesses in Iowa. Among these illnesses are influenza, tuberculosis and foodborne illnesses caused by toxigenic E. coli and Salmonella bacteria.

A key tool used to help identify clusters of bacterial illness is pulsed-field gel electrophoresis, which extracts DNA fingerprints of pathogens. It is especially useful in tracing foodborne illnesses. The Hygienic Laboratory uses pulsed-field gel electrophoresis in its daily work to combat foodborne illness.

"The Lab plays a very important role in stopping the transmission of foodborne pathogens," said Michael Pentella, Ph.D, associate director who leads the Disease Control Division. "By detecting pathogens and further characterizing the isolates by pulsed-field gel electrophoresis to determine if the strains are related, the information serves to tell the epidemiologists if they are on the right track to find the contaminated food stuff."

Similar to fingerprints in a criminal case, these fingerprints from foodborne pathogens are submitted to a central international registry at the CDC known as PulseNet. When DNA fingerprints from bacteria in one part of the world match those from bacteria in another part of the world, it can be an early warning that an outbreak is under way.

Toxigenic E. coli and Salmonella organisms are some of the most infamous causes of foodborne illnesses. The Centers for Disease Control and Prevention estimated in 2011 that approximately one in every six Americans will became sick from foodborne illnesses.

In prominent cases of Salmonella linked to peanut butter and deli meat, Iowa played a key role in the investigations. In both cases, the Hygienic Laboratory was the first to isolate the outbreak strain in the food product that confirmed the cause of the outbreak.

In 2012, one of the most notorious culprits was E. coli linked to raw clover sprouts that sickened people in 11 states from Christmas 2011 through March 3, 2012. Cases of Shiga toxin-producing Escherichia coli serogroup O26 (E. coli STEC O26) were first seen in Iowa where they were detected by the Hygienic Laboratory.

"Lab surveillance was absolutely critical for recognition, source identification, and final recall of the lot of sprouts linked to this outbreak," said Nancy Hall, Environmental Microbiology manager. "This type of E.coli is very difficult to identify in stool cultures, so laboratories must follow CDC's recommendation for sending toxin positive stools to [their public health laboratories] so that this unusual disease-producing E.coli can be isolated and identified for DNA fingerprinting.

"Once patient cases are identified by this means, epidemiologists can then administer questionnaires to discover common sources," Hall adds. "In this outbreak, it was a certain lot of sprouts served at [franchise sandwich] restaurants in more than 11 states, including Iowa."

Through the coordinated efforts of physicians, clinical labs, the Iowa Department of Public Health and the Hygienic Laboratory, the spread of the outbreak was stopped. It was a reminder that sprouts often are repeat offenders in causing foodborne illness.

"There have been many 'sproutbreaks' in the last couple years," Hall said. "The bacteria cannot easily be rinsed off the product because it is encapsulated in the seed. CDC recommends that the very young, very old and pregnant women should not consume raw sprouts."

The CDC maintains an Outbreak Response Team website that tracks the foodborne illnesses, maps the incidence in each state and graphs the epi curve - a daily count of the of people sickened. The website reflects the work of surveillance teams and the commitment of state public health laboratories to arrest the development of foodborne outbreaks.