To determine the burden of Salmonella infections in the United States, Foodborne Diseases Active Surveillance Network (FoodNet) investigators conducted population-based active surveillance for culture-confirmed Salmonella infections during 1996-1999 at FoodNet laboratories. In addition, all clinical microbiology FoodNet laboratories were surveyed to determine their practices for isolating Salmonella. Telephone interviews were also conducted among residents of the FoodNet sites to determine the proportion of persons with diarrheal illness who sought medical care and the proportion who submitted stool specimens for bacterial culture. Using our model, we estimated that there were 1.4 million nontyphoidal Salmonella infections in the United States, resulting in 168,000 physician office visits per year during 1996-1999. Including both culture-confirmed infections and those not confirmed by culture, we estimated that Salmonella infections resulted in 15,000 hospitalizations and 400 deaths annually. These estimates indicate that salmonellosis presents a major ongoing burden to public health.
This study was performed to better understand and more precisely quantify the amount and burden of illness caused by acute diarrhoea in the United States today. A telephone-based population survey was conducted between 1 July, 1996, and 31 June, 1997, in sites of the Foodborne Diseases Active Surveillance Network (FoodNet). The overall prevalence of acute diarrhoea in the 4 weeks before interview was 11%, giving a rate of 1.4 episodes of diarrhoea per person per year. The rate of diarrhoeal illness defined as a diarrhoeal episode lasting longer than 1 day or which resulted in significant impairment of daily activities was 0.7 per person per year. It can be concluded that acute diarrhoea is common and represents a significant burden of illness in the United States. Our data on self-reported diarrhoea, when generalized to the entire nation, suggests 375 million episodes of acute diarrhoea each year in the United States. Many of these episodes are mild. However, our data also indicate that there are approximately 200 million episodes of diarrhoeal illness each year in the United States.
In a large outbreak of E. coli O157:H7 infections among visitors to a dairy farm, predominantly children, high rates of carriage of E. coli O157:H7 among calves and young cattle most likely resulted in contamination of both the animals' hides and the environment.
In 2000, we surveyed microbiologists in 388 clinical laboratories, which tested an estimated 339,000 stool specimens in 1999, about laboratory methods and policies for the routine testing of stool specimens for Salmonella, Shigella, Campylobacter, and Vibrio species, Yersinia entercolitica, and Escherichia coli O157:H7. The results were compared with those of similar surveys conducted in 1995 and 1997. Although these laboratories reported routinely testing for Salmonella, Shigella, and Campylobacter species, only 57% routinely tested for E. coli O157:H7, 50% for Y. entercolitica, and 50% for Vibrio species. The mean proportions of stool specimens that yielded these pathogens were as follows: Campylobacter, 1.3% of specimens; Salmonella, 0.9%; Shigella, 0.4%; and E. coli O157:H7, 0.3%. The proportion of laboratories that routinely tested for E. coli O157:H7 increased from 59% in 1995 to 68% in 2000; however, the proportion of stool specimens tested decreased from 53% to 46%. E. coli O157:H7 should be routinely sought in stool specimens submitted for microbiologic culture.
In 2000, shigellosis traced to a commercially prepared dip developed in 406 persons nationwide. An ill employee may have inadvertently contaminated processing equipment. This outbreak demonstrates the vulnerability of the food supply and how infectious organisms can rapidly disseminate through point-source contamination of a widely distributed food item.
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