Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (147 page)

   
Viral culture
is also of limited utility because of long turnaround time as well as the limited availability of the specialized viral cultures required for enteric viruses that may be isolated in culture. Some clinical laboratories may provide viral culture testing to rule out enteric adenoviruses (serotypes 40 and 41).

   
Antigen detection
testing is available for several enteric viruses and provides reliable detection of rotavirus and enteric adenovirus in stool specimens.

   
Molecular diagnostic
tests now play an important role in the detection of enteric virus infection because of their high sensitivity and specificity, as well as short turnaround time for most assays. Many Public Health and Reference Laboratories offer testing for relevant viruses, and an increasing number of approved assays are becoming commercially available.

   
Parasites: O&P testing
is not cost-effective for routine testing of patients with gastrointestinal complaints but should be considered in patients with

   
Persistent diarrhea

   
Specific epidemiologic
risks, like travel to regions with a high endemic rate of enteric parasitic infections, exposure to infants in day care centers, diarrhea in men who have sex with men, patients with HIV infection, and patients who develop diarrhea during a waterborne or other regional outbreak of diarrhea caused by parasitic pathogens

   
Sensitive and specific
stool antigen testing is available for
Cryptosporidium
,
Giardia
, and
E. histolytica
. Antigen testing may serve as cost-effective initial testing for patients who require testing to rule out parasitic infection. Because ova and parasites may be shed intermittently, three specimens for O&P testing should be submitted, separated by at least 24 hours, over 3–6 days,
if needed.

   
Serology
: Detection of specific IgM and IgG is used for diagnosis of acute hepatitis A virus infection. Serology plays a minor role in the diagnosis of acute infection by other enteric pathogens. However, patient seroconversion may provide important diagnostic information during the convalescent phase, especially for epidemiologic investigations regarding the cause or scope of a potential epidemic of gastrointestinal disease.

   
Toxins: C
linical laboratories do not routinely offer testing for detection of specific toxins, like botulinum toxin, in food or patient specimens. Testing for toxins is typically performed by a Public Health Laboratory, or other specialized reference laboratory, and is usually performed only as part of a formal epidemiologic investigation.

   Conclusion

It is important for health care providers to

   Consider the possibility of foodborne illness in evaluating a patient’s illness.