By Craig W. Hedberg, PhD
University of Minnesota
Editor's Note: This commentary is a follow-up to "Commentary: Blame the public health system for prolonging listeriosis outbreak," published Oct 9, 2002.
Nov 27, 2002 – Seven weeks ago, I wrote a commentary that questioned the ability of the public health system to respond to a large, multistate outbreak of listeriosis. The commentary was not meant as a criticism of the professionalism, dedication, or commitment of the investigators to finding the source of this outbreak. It was meant as a challenge to the public health system to develop and use new methods to more rapidly investigate these major public health events so as to identify and control the source. As we move further into the era of bioterrorism threats, this will be more important than ever.
With respect to the current investigation, however, I was mistaken on one important point. In response to previous outbreaks of listeriosis associated with hot dogs and deli meats, the Center for Disease Control and Prevention (CDC) has begun to use a standardized outbreak investigation questionnaire that does seek detailed brand name and location of purchase information for these foods. Thus, the outbreak investigation is designed to test the hypothesis that these foods may be the source. Given the current epidemiology of listeriosis, this is a good thing. It also represents the type of approach I was trying to encourage.
Since my original commentary, the US Department of Agriculture (USDA), CDC, and their partners in the states have identified not one, but two, turkey processing plants as likely sources of the outbreak. The investigation continues. However, the major overall question remains: How can we identify these outbreaks sooner and investigate them more swiftly?
Listeria presents many unique challenges. The long incubation period means that 4 weeks of food history must be assessed. Many of the potential vehicles, such as sliced deli meats, are commodities to the consumer .Typically, the consumer goes to the deli counter and buys a pound of sliced turkey without much concern for when or where it was actually produced. By the time an outbreak is recognized and an investigation begun, many of the details will have passed from memory and many of the records placed in storage, lost, or destroyed. So where do we go from here?
As the incidence of listeriosis has declined, the importance of outbreaks, from both a public health and an economic perspective, has increased.The best way to detect outbreaks is to assure that all human Listeria isolates are rapidly forwarded to public health laboratories, are promptly subtyped, and the subtype information reported to PulseNet and to the respective local, state, and CDC epidemiologists responsible for Listeria surveillance.
The best way to document food histories is to interview the patient as soon as the case is reported. This means that patients should be interviewed before there is any indication that they may be part of an outbreak. If all listeriosis patients were routinely interviewed, comparisons of food histories could be made between outbreak and sporadic cases as soon as an outbreak were identified. This would speed up the investigation process and increase the likelihood of getting reliable information.
We need to improve the speed and completeness of our passive reporting system for Listeria. To do this we need to create meaningful incentives to stimulate prompt and complete reporting. One incentive is to demonstrate that reporting leads to public health interventions that lead to prevention of disease. Another incentive might be to formally recognize the contributions of clinical laboratories and local and state investigators through a special "Listeria Surveillance Award" that could be conferred by CDC. Finally, a special surveillance fund could be established to compensate state and local agencies for their efforts to promptly follow up with individual case reports. At current incidence levels, payment of $1,000 per case would cost less than $1 million. Given the costs associated with current outbreaks and recalls, this would be a modest investment.
It may be a dangerous precedent to establish a system of paying for public health investigations by the case, but the unique challenges of Listeria call for unique responses. As the food safety system reduces the overall risk of Listeria, a higher proportion of cases are likely to be part of detectable outbreaks. Thus, responding to these outbreaks will be ever more important. At the same time, having fewer cases reported to state and local health agencies will mean more competition for public health resources to promptly respond to the few cases that are reported. It is to address this concern that a special case can be made for a unique funding program for Listeria surveillance.
Dr Hedberg is an associate professor in the Division of Environmental and Occupoational Health, School of Public Health, University of Minnesota, Minneapolis.