Dr. Braden emphasized that the benefits of CIDTs are impressive, especially for clinical care. In addition to yielding results faster, he stressed that culture-independent diagnostic testing is probably more sensitive than culture testing; a single test can also detect or rule out multiple types of pathogens (such as bacteria, viruses, and parasites); and this technique is often the only practical way to detect viral pathogens, he said.
However, these tests also have drawbacks, said Dr Frieden. They do not provide some of the more detailed information that culture tests can provide. For example, because CIDTs do not yield isolates that can be further tested, these tests cannot help clinicians to determine whether a bacterial pathogen is resistant to certain antibiotics.
Reflex culturing (culturing a specimen after CIDT produces a positive result) is therefore often needed to further characterize the pathogen and tailor treatment, Dr Braden added.
CIDT also involves other drawbacks, he noted, especially because positive results can be difficult to interpret in some situations. For example, even DNA from dead microorganisms can produce a positive result. Clinicians may therefore be challenged to know whether a patient is still contagious, and may therefore be unclear about whether an adult patient should return to work, or a child patient to a day care facility. Also, because a single test can detect multiple pathogens, it may identify some that are not causing the patient’s current illness. According to one study, more than 30% of positive tests detected multiple enteric pathogens, said Dr Braden.
Nevertheless, pathogen characterization is an important component of food safety. “Each year, 48 million people get sick, 128,000 are hospitalized, and 3,000 die from food-borne diseases,” Dr Braden emphasized.