Academic journal article Journal of Environmental Health

Conducting Effective Foodborne-Illness Investigations

Academic journal article Journal of Environmental Health

Conducting Effective Foodborne-Illness Investigations

Article excerpt

Abstract

Hazard analyses during an outbreak investigation must focus on identifying the source and mode by which the implicated food has been contaminated, as well as on the situations that have allowed the contaminants to survive heat processing or other potentially lethal processes and that have permitted or promoted propagation of the pathogen. This article offers practical techniques for detecting such events. The information can be used to prevent further occurrences at the location where a mishandling has occurred and to build a surveillance database. Factors that contribute to foodborne outbreaks can be incorporated into the database, which can guide inspections, hazard analyses, promulgation of food regulations, training of public health personnel and food workers, and education of the public.

Introduction

Epidemiologic data generated from calculations of rates and statistical analyses may suggest hypotheses of etiologic agent, place of eating, perhaps a meal, and perhaps a food. The task of the field investigator is to prove or refute the validity of these hypotheses, or to gather data from which to formulate other hypotheses.

Investigative Procedures

Anticipating from Initial Data Where to Focus Attention

At the outset of an on-site investigation at the place of a presumed mishandling, investigators should concentrate on contamination, survival, and/or propagation of the etiologic agents under suspicion. If there is a microbial- or chemical-caused disease, contamination with the etiologic agent has to have occurred. If the disease is microbial, either there was no heat process (e.g., fresh produce or shellfish was eaten raw) or the pathogen survived a process such as cooking or heat processing or the contamination occurred after the process. If the disease is bacterial, the pathogen (unless highly virulent or affecting highly susceptible persons) must propagate to attain a population or to produce a quantity of toxin that overwhelms the susceptibility/resistance threshold of the host. If the disease is parasitic, the parasite may have to develop into an infectious stage. Therefore, at the sites of production, processing, and/or preparation, priority activities will be

* to find the source (whether within the food establishment or from before the food arrived there) and mode of contamination;

* to determine whether the process killed the pathogens, reduced their populations, or permitted survival; and

* to determine whether the pathogen propagated rapidly, slowly, or not at all.

With this attitude and with appropriate equipment and supplies, an investigator is ready to work on site [1]. Table 1 shows sources and modes of contamination, and further help is available in a manual of procedures for investigating foodborne illness; the procedures involve anticipating contamination, survival, and growth [1].

Proving the Illness Has Been Caused by the Etiologic Agent Under Consideration

In this step, investigators will need to obtain stool, blood, or other appropriate specimens from those who are ill and whose syndrome and incubation period are typical of the disease under consideration. The specimens then can be analyzed for the suspected etiologic agent [1,2]. This step is essential in confirming a diagnosis; otherwise the investigation will result in the classification "unknown etiology." After isolation of a pathogen, if applicable (as in cases of Salmonella and Escherichia coli contamination), investigators should request that isolates be typed to identify the serovar or strain. Further identification of the strain is possible with markers such as phages, DNA probes, and antibiograms, or with a number of other techniques [1].

Confirming the Vehicle and Eliminating Other Possible Vehicles

The next step is to calculate attack rates for those who have eaten specific foods and those who have not. …

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