FoodNet has conducted population-based surveillance for laboratory-confirmed cases of infection caused by Campylobacter, Listeria, Salmonella, Shiga toxin-producing Escherichia coli (STEC) O157, Shigella, Vibrio, and Yersinia since 1996 (a 6 month pilot program was conducted between July-Dec 1995); Cryptosporidium and Cyclospora since 1997; and STEC non–O157 since 2000. FoodNet is an active surveillance system, meaning that public health officials routinely communicate with the >650 clinical laboratories serving the surveillance area to identify new cases and conduct periodic audits to ensure that all cases are reported.
A case is defined as isolation (for bacteria) or identification (for parasites) of an organism from a clinical specimen. Once a case is identified, FoodNet personnel at each site collect information about core variables and enter this information into an electronic database. They transmit data to CDC monthly. Hospitalizations occurring within 7 days of the specimen collection date are recorded, as is the patient’s status (alive or dead) at hospital discharge (or at 7 days after the specimen collection date if the patient is not hospitalized). Whether the patient traveled abroad within 7 days of illness onset is captured routinely for all Salmonella and STEC O157 cases.
FoodNet also conducts surveillance for cases of hemolytic uremic syndrome (HUS) through a network of pediatric nephrologists and infection-control practitioners who report all illnesses diagnosed as HUS on the basis of clinical findings. FoodNet staff review hospital discharge data for pediatric HUS cases to validate surveillance reports and identify additional cases. HUS cases are identified using ICD-9-CM codes specifying HUS, acute renal failure with the hemolytic anemia and thrombocytopenia, or thrombotic thrombocytopenic purpura with diarrhea caused by an unknown pathogen or E. coli.
In addition to routine surveillance, special surveillance projects are conducted. In 2002, two sites conducted population-based surveillance for reactive arthritis associated with Campylobacter, Salmonella, Shigella, Yersinia, and STECinfections. In 2009, FoodNet began to collect information on STEC and Campylobacter casesthat are identified by culture-independent methods. These data will allow FoodNet to monitor the use of these methods and assess the need for multi-level case definitions. Also in 2009, a pilot surveillance program for community-acquired Clostridium difficile infections was conducted in Connecticut and New York. In 2010, a pilot surveillance program for Cronobacter sakazakii infections was conducted in selected sites.
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