PulseNet is the network used by the Centers for Disease Control and Prevention (CDC) to match cases of illness to find outbreaks so that officials can find the common source, recall contaminated food, and prevent more illnesses.
The surveillance system is a molecular subtyping network of state public health and food regulatory agency laboratories designed to identify and facilitate investigation of foodborne illness outbreaks.
Results will help public health officials, policymakers, and the public assess the health and economic returns from maintaining, and potentially expanding, the program.
Study backs up anecdotal evidence
John Besser, deputy chief of CDC’s enteric disease laboratory branch, said the work gives it hard figures on what it has known anecdotally for years.
“PulseNet has been making food safer for 20 years and these hard numbers make it easier to show. Improvements in epidemiology help account for some of the effect we saw, investigations by PulseNet create an environment where there is more epidemiological follow-up,” he told FoodQualityNews.
“It is not always possible to demonstrate the benefits like in this study. It is always useful to show success and there is tremendous potential yet to be tapped.
“We will measure the impact of whole genome sequencing and is it cost effective – that is the first priority. Down the road we may examine other pathogens such as Campylobacter and Shigella.
“PulseNet investigations are an important part of the overall food safety program and help us identify a problem that would otherwise not be identified and we are able to provide industry and regulatory agencies with the data they need.”
Two approaches were used: a “Recall” model to assess the direct effects of faster identification of outbreaks on eating contaminated product and resulting illness reduction and a “Process Change” model to capture the indirect effects from enhanced outbreak identification on illnesses averted due to incentives and information used by industry and government.
As PulseNet was adopted by states in different years it creates ideal conditions for evaluation.
It is unclear how many illnesses are prevented because of industry improvements or how many are avoided due to better-informed government and consumers.
Robert Scharff of Ohio State University and Craig Hedberg of the University of Minnesota worked on the study. Scharff said the calculations probably underestimate the impact of PulseNet.
“We did not examine whether illnesses from pathogens outside of the three in question were reduced as a result of industry efforts, though they likely were,” he said.
“We aren’t able to estimate the cost to industry from remedial actions. These could be significant for affected companies, but are lower than the costs of having foodborne illnesses associated with their products.”
Data from 1994 and 2009 were analyzed between 2010 and 2015. Conservatively, accounting for underreporting and under diagnosis, 266,522 illnesses from Salmonella, 9,489 from E. coli, and 56 due to Listeria monocytogenes are avoided annually. This reduces medical and productivity costs by $507m.
Direct effects from improved recalls reduce illnesses from E. coli by 2,819 and Salmonella by 16,994, leading to $37m in costs averted.
Learning from outbreaks
PulseNet identifies about 1,500 clusters of illness caused by E. coli, Listeria and Salmonella, including about 25 multistate outbreaks linked to food every year.
Outbreaks tied to peanut butter have led to standards to keep Salmonella out of processed foods, and outbreaks linked to ground poultry and chicken parts resulted in standards that reduced levels of bacteria in raw poultry.
It uses comparison of pulsed field gel electrophoresis (PFGE) patterns but whole genome sequencing (WGS) is providing more accurate fingerprinting for a better match among bacteria.
“We’re in the midst of an exciting time of technological change that will help stop more foodborne disease outbreaks and help keep people healthy,” said Robert Tauxe, director of CDC’s Division of Foodborne, Waterborne, and Environmental Diseases.
“We’re working on methods that will make PulseNet faster, perhaps allowing patients to learn they’re part of an outbreak within a few days of getting sick.”
However, doctors are increasingly using culture-independent diagnostic tests to diagnose foodborne illness.
These tests present a challenge because they give quick results but don’t provide the living bacteria the network needs to create and analyze DNA fingerprints so it can’t find outbreaks.
CDC said it is working with public health officials, diagnostic labs, test manufacturers, and doctors on the issue.
Tom Frieden, CDC director, said hundreds of thousands of people are able to stay healthy as a result of the early warning system.
“Advanced molecular detection technology, such as whole genome sequencing, is enhancing CDC PulseNet’s ability to save lives right now – and promises to save more American lives in the future.”
PulseNet was created after a 1993 outbreak of E. coli O157 that sickened more than 700 people and killed four children. Experts determined that it could have been stopped sooner if all public health labs did the same DNA fingerprinting tests and shared results.
Source: American Journal of Preventive Medicine
Authors: Robert L. Scharff, John Besser, Donald J. Sharp, Timothy F. Jones, Gerner-Smidt Peter and Craig W. Hedberg