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Use of culture-independent tests may hinder surveillance of enteric infections
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The increased use of culture-independent diagnostic tests for bacterial enteric infections may be problematic as cultures are necessary for subtyping and public health surveillance, according to a report in MMWR.
Currently, clinical labs obtain culture isolates, which are forwarded to public health laboratories for additional testing, according to the report. As labs increasingly adopt culture-independent diagnostic tests (CIDTs), the burden for cultures will fall on public health labs.
“As more clinical laboratories adopt CIDTs, the collection and detailed characterization of bacterial isolates that support public health activities will fall more heavily on public health laboratories,” CDC researchers wrote. “The increased reliance on CIDTs will create a burden for public health laboratories and will have a significant impact on clinical practice, outbreak detection and the ability to monitor disease burden and trends.”
The researchers examined surveillance data from the CDC’s FoodNet and data from surveys of FoodNet clinical labs to characterize the use of CIDTs and culture for bacterial enteric infections. The surveillance data included culture-confirmed and positive CIDT reports of Campylobacter, Salmonella, Shiga toxin–producing Escherichia coli (STEC), Shigella, Vibrio and Yersinia infections from January 2012 to December 2013. The lab surveys were conducted from January to March 2014.
There were 38,666 culture-confirmed cases and positive CIDTs from 2012 to 2013. Of 5,614 positive CIDTs reported, 46% were not confirmed by culture. There were 2,497 positive CIDTs of Campylobacter, of which 22% were culture confirmed. The incidence of culture-confirmed infections was 14.1 per 100,000 population, compared with 2.1 for positive CIDTs with no culture or negative culture.
Among 2,409 positive CIDTs of STEC, 92% were confirmed by culture. The incidence of STEC was 2.4 per 100,000 population for culture-confirmed infections vs. 0.21 for positive CIDTs with no culture or negative culture. There were 308 positive CIDTs of Salmonella; 37% were confirmed by culture. The incidence was 16 per 100,000 population for culture-confirmed infections, compared with 0.2 for positive CIDT with no culture or negative culture.
From the survey data, the researchers found variety in the use of CIDTs by pathogen, which were most often used for Campylobacter and STEC. For Campylobacter, 45 labs (10%) used only CIDTs to detect the organism, and the remainder used only culture or both methods. For STEC, 73 labs (19%) used only CIDTs to detect the organism.
“With many recent approvals of CIDTs that offer advantages to clinicians and clinical laboratories over traditional culture-based methods, many clinical laboratories are in the process of switching to CIDTs and accelerated use is anticipated over the next year,” the researchers wrote. “Taken together, these findings warrant increased attention to surveillance for all bacterial enteric pathogens and critical examination of the results of CIDTs.” – by Emily Shafer
Disclosure: The researchers report no relevant financial disclosures.
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