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PulseNet Ups Ante In Food Safety Battle

Jim Prevor’s Perishable Pundit, October 6, 2006

The reason the industry is going to have to get much better at food safety is because unless we do, publicly reported outbreaks are going to become more frequent and more severe.

This is not because things will be less safe; it is because the states are getting better at the use of PulseNet. What is PulseNet?

PulseNet is a national network of public health and food regulatory agency laboratories coordinated by the Centers for Disease Control and Prevention (CDC). The network consists of: state health departments, local health departments, and federal agencies (CDC, USDA/FSIS, FDA).

PulseNet participants perform standardized molecular subtyping (or “fingerprinting”) of foodborne disease-causing bacteria by pulsed-field gel electrophoresis (PFGE). PFGE can be used to distinguish strains of organisms such asEscherichia coliO157:H7, Salmonella, Shigella, Listeria, or Campylobacter at the DNA level. DNA “fingerprints,” or patterns, are submitted electronically to a dynamic database at the CDC. These databases are available on-demand to participants — this allows for rapid comparison of the patterns.

Why do we have something called PulseNet?

In 1993, a large outbreak of foodborne illness caused by the bacterium Escherichia coli O157:H7 occurred in the western United States. In this outbreak, scientists at CDC performed DNA “fingerprinting” by pulsed-field gel electrophoresis (PFGE) and determined that the strain ofE. coliO157:H7 found in patients had the same PFGE pattern as the strain found in hamburger patties served at a large chain of regional fast food restaurants. Prompt recognition of this outbreak and its cause may have prevented an estimated 800 illnesses. As a result, CDC developed standardized PFGE methods and in collaboration with the Association of Public Health Laboratories (APHL), created PulseNet so that scientists at public health laboratories throughout the country could rapidly compare the PFGE patterns of bacteria isolated from ill persons and determine whether they are similar.

For most of human history, foodborne illness was typically traced back to public events. You would read in the papers about a convention or catering hall in which everyone had dinner and a lot of people got sick.

This is not because most foodborne illness took place at communal gatherings. It is because only those types of events produced the critical mass of people going into the same doctors and hospitals to allow tracing back to a source.

In other words, if you get 10,000 people sick but they are evenly spread across the country due to a product issue, and those who go to doctors and hospitals go to a random selection of doctors and hospitals who don’t know anything about the other sick people, you would have never known that a product got 10,000 people sick.

On the other hand, if you have 1,000 people get sick at a big local fund-raising banquet, they go to the one or two local hospitals and a few local doctors, you will probably quickly discover a pattern showing that all these people were at this event.

PulseNet recently identified cases within the spinach/E. coli outbreak. The Idaho Department of Health & Welfare explained it this way:

In the recent E. coli outbreak, Wisconsin, Oregon and Idaho shared test results over PulseNet. PulseNet, an internet-based system, allows the posting of genetic test results on a secured database shared by all states and the CDC in Atlanta. Using this web-based approach, matching lab results were linked between states much faster than the traditional approaches allowed. This resulted in a much quicker public health response. By utilizing lab results, health officials were able to contact the affected people and determine that fresh spinach consumption was the likely source of the E. coli infections. The faster the source of the contamination can be discovered the more quickly health officials can move to prevent others from getting sick.

Before PulseNet was available, the traditional answer to determining a source of contamination was lengthy interviews with individuals about where they had eaten, when they had eaten, what they had eaten and with whom they may have had contact. The information would at some point be shared with other states if a potential link was suspected. Given enough interviews, experienced epidemiologists might discover a common source of infection. PulseNet and the rapid sharing of information over the web have increased the accuracy and speed of the lab process and provided opportunities to reach the public more quickly.

“This is a huge improvement in our efforts to protect people and provide safe sources of food,” concludes Hudson. “This is really about good science and really good public health.”

You can read the press release here.

Although PulseNet was conceived over 10 years ago, the states have become much more adept at its use in the last several years. We can expect the technology to speed up and the skill level with which PulseNet is used to improve. This has two consequences for the perishable food trade:

First, many foodborne illnesses that in the past were never identified as part of any official “outbreak” will now be so classified.

Second, whereas in the past, most outbreaks that were identified were not identified until after the “use by” or “expire” dates had passed and so recalls were pointless — now we can expect quick identification of problems and an enormous increase in recalls.

In financial terms, this means the cost of occasional outbreaks of foodborne illness just went way up. So it will now pay to spend a lot more money to reduce their frequency and intensity.

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