Epidemiology of foodborne diseases: a worldwide review

Acute foodborne disease infections and intoxications are much more of a concern to governments and the food industry today than a few decades ago. Some of the factors that have led to this include the identification of new agents that have caused life-threatening conditions; the finding that traditional agents are being associated with foods that were of no concern previously: an increasing number of large outbreaks being reported; the impact of foodborne disease on children, the aging population and the immunocompromised; migrant populations demanding their traditional foods in the countries of settlement; the ease of worldwide shipment of fresh and frozen food; and the development of new food industries, including aquaculture. However, to meaningfully monitor increases or decreases in foodborne disease requires an effective surveillance system at the local, national and international levels. To date, resources have been limited for most countries and regions to do this, and our current knowledge is based, for the most part, on passive reporting mechanisms. Laboratory isolation data and reports of notifiable diseases have some value in observing timely changes in case numbers of some enteric diseases, but they usually do not indicate the reasons for these trends. Special epidemiological studies are useful for the area covered, but it is often questionable whether they can be extrapolated to other areas or countries. Outbreak investigations tell us that a certain set of circumstances led to illness and that another outbreak may occur under similar but not necessarily identical conditions. Control programmes have often been triggered by the conclusions from investigations of specific outbreaks. Unfortunately, the agent/ food combination leading to illness in many of the reported incidents were not predicted from existing databases, and no doubt foodborne agents will continue to surprise food control agencies in the foreseeable future. Nevertheless, data from around the world do show some common elements. Salmonella is still the most important agent causing acute foodborne disease, with Salmonella enteritidis and S. typhimurium being of most concern. Foods of animal origin, particularly, meat and eggs, were most often implicated. Desserts, ice cream and confectionery items were products also mentioned, but some of these would have egg as a raw or incompletely cooked ingredient. Incidents most frequently occurred in homes or restaurants, and the main factors contributing to outbreaks were poor temperature control in preparing, cooking and storing food. Clostridium botulinum, Salmonella and VTEC are more frequently documented in industrialized than in developing countries. ETEC, EPEC, Shigella, Vibrio cholerae and parasites are the main scourges in developing countries, but it is uncertain how many cases are attributed to food, to water or to person-to-person transmission. The apparent decrease of S. aureus and C. perfringens outbreaks in industrialized countries may be related to improved temperature control in the kitchen. An increasing number of illnesses are international in scope, with contamination in a commercial product occurring in one country and affecting persons in several other countries, or tourists being infected abroad and possibly transmitting the pathogen to others at home. For Salmonella, a rapid alert and response coordination is being encouraged through Salm-Net and other international programs. However, unless such a network is worldwide, tracking clusters of illnesses is going to fall on the countries where the first cases occur, and some of these have very limited resources for investigation and control. It was heartening to see funds recently being allocated to foodborne disease surveillance and control in several industrialized countries, but the same commitment is required by the World Health Organization for the international community.