Rising use of culture-independent diagnostic tests led to more reported cases of Cryptosporidium and non-O157 Shiga toxin–producing Escherichia coli (STEC) last year when compared with previous years, according to data from The Centers for Disease Control and Prevention’s (CDC) Foodborne Diseases Active Surveillance Network, also known as FoodNet.
Jennifer Huang, MPH, of the Division of Foodborne, Waterborne, and Environmental Diseases in the National Center for Emerging and Zoonotic Infectious Diseases at the CDC, and colleagues wrote in Morbidity and Mortality Weekly Report that the confirmed infections per 100,000 people of STEC non-O157 E coli increased by 40%, and Cryptosporidium reports increased by 57%. The researchers reported that no substantial changes were seen in other types of infections.
The researchers noted a large increase in the number of laboratories that test for STEC non-O157, which rose to 74% in 2015 compared with 55% in 2012.
According to the report, FoodNet detected 20107 cases of foodborne illness infections in 2015, which resulted in 4531 hospitalizations and 77 deaths. Salmonella accounted for the highest number of cases, with 7728 confirmed. Of the 88% of Salmonella cases that were serotyped (6827), the most common were Enteritidis (20%), Newport (12%), and Typhimurium (11%).
The next highest cause of foodborne illness infection was Campylobacter with 6309 cases. Shigella accounted for 2688 cases, Cryptisporidium 1612, STEC non-O157 796, STEC O157 463, followed by Vibrio (192), Yersinia (139), Listeria (116), and Cyclospora (64), according to the CDC researchers.
“Increasing use of culture independent diagnostic tests (CIDTs) affects the interpretation of public health surveillance data and the ability to monitor progress towards prevention efforts,” the researchers wrote. This is important, because Foodnet only uses confirmed data from cultures to measure incidence.
There were some limitations to this study, specifically that increased use of CIDTs might affect the number of infections reported, which would affect incidence. Next, the researchers noted that CIDT test brand quality varies, and this could also affect results. Third, healthcare-seeking behaviors and access to care may be a factor affecting outcomes. Fourth, the researchers stated that some of these infections that have other methods of transmission may not have been caused by food, and lastly, these could be year-to-year variations rather than long-term trends.
Despite these limitations, CIDTs are extremely useful because of their ability to rapidly detect infection and their ability to detect diseases not currently identified by current laboratory methods, such as enterotoxigenic E coli, according to the researchers.
In an interview with Infectious Disease Advisor, Mary Patrick, MPH, an epidemiologist in CDC’s Enteric Diseases Epidemiology Branch, said that the strongest implications of these findings are for public health practice.
“Without a bacterial culture, public health officials cannot get the detailed information about the bacteria needed to help find outbreaks, check for antibiotic resistance, and track foodborne disease trends,” she said. “The increased use of CIDT could affect public health officials’ ability to monitor trends and detect outbreaks. We encourage clinical laboratories to work with their public health laboratories to make sure a culture is done whenever a CIDT indicates that someone with diarrheal illness has a bacterial infection.”
1. Huang JY, Henao OL, Griffin PM, et al. Infection with Pathogens Transmitted Commonly Through Food and the Effect of Increasing Use of Culture-Independent Diagnostic Tests on Surveillance — Foodborne Diseases Active Surveillance Network, 10 US Sites, 2012–2015. MMWR. 2016;65:368–371.