Rapid Diagnostic Tests for Infectious Diseases

In the context of infectious diseases, the term rapid diagnostic test (RDT) most commonly refers to lateral-flow, immunochromatographic tests used to detect certain infections. More generally, such assays may be described as point-of-care (POC) tests. Although there are no accepted criteria for what constitutes an RDT or POC test, published definitions frequently focus on performance time and simplicity. Pathogen-specific or syndrome-based tests are considered RDTs if they meet either or both of the following criteria:

The test can be incorporated into a POC testing protocol for a given infection or clinical syndrome. Such assays have relatively short performance times, yield results that will affect clinical decision making, and allow management decisions to be made during the same encounter.
The test can be performed under a certificate of waiver under the Clinical Laboratory Improvement Amendments of 1988, so-called “waived” tests (Table 11-5).

Certain tests that meet this definition may not be used in a manner compatible with POC testing. For instance, an increasing number of waived, sample-to-answer molecular diagnostics (nucleic acid amplification tests, such as PCR or RT-PCR) are becoming available. At a given institution, though, such assays might only be performed in a central laboratory at specific times, thereby limiting their utility in a POC testing protocol. These assays typically require dedicated, bench-top equipment for performance. As such, adding capacity at individual clinical sites may not be feasible.

Table 11-5. Selected rapid diagnostic tests for pathogens in the returning traveler
Syndrome	Pathogen	Specimen	Additional information
Lateral-flow immunochromatographic tests and small panels
Systemic febrile illness	Ebola virus ¹	Whole blood	Received emergency use authorization by FDA and WHO. May not be appropriate for excluding illness in early infection.
	Dengue virus ¹	Serum	Not FDA-cleared. Highly variable diagnostic performance. Antibodies may cross-react with other flaviviruses.
	Malaria ¹	Whole blood	Best performance characteristics for Plasmodium falciparum infections. Many versions may be available in endemic areas.
Gastrointestinal infections	Norovirus, rotavirus, adenovirus ¹	Stool sample	Available in the United States individually or in combination. Adenovirus rapid tests are approved for ocular specimens.
Respiratory infections	Group A Streptococcus	Throat swab	Rapid antigen and molecular tests ² available; both are specific but molecular tests have improved sensitivity.
	Influenza	NP or throat swab	Rapid test sensitivity 50%–70%; negative testing should not direct treatment.
	Legionella pneumophila ¹	Urine	Only detects serogroup 1. Recommended by IDSA for patients with more severe disease.
	Respiratory syncytial virus	NP or throat swab	Accurate antigen assays, recommended if results will affect management.
	Streptococcus pneumoniae	Urine	Recommended by IDSA for use in certain patient populations.
Sexually transmitted infections	Chlamydia trachomatis and Neisseria gonorrhea ¹	Urine, vaginal swab	Molecular tests remain gold standard; a sample-to-answer molecular assay is available. ¹^, ²
	HIV	Whole blood, oral fluids	Antibody and antibody/antigen kits available. Molecular testing preferred for acute infection.
	Treponema pallidum	Whole blood	Antibody detection, may not be appropriate for acute infections.
	Trichomonas vaginalis	Vaginal swab	Rapid antigen testing is specific with sensitivity approximately 90%.
	BV pathogens	Vaginal swab	Identifies increased sialidase activity, an enzyme associated with BV pathogens.
Multiplex molecular panels
Gastrointestinal pathogens	Includes common viruses, bacteria, and parasites ¹^, ²	Stool sample	Sensitive, certain positive results may be unrelated to active infection.
Respiratory pathogens	Includes common viruses and atypical bacteria ²	NP swab	Pathogens may have prolonged shedding time; positive results may not rule out infection from other pathogens.
Abbreviations: BV, bacterial vaginosis; FDA, US Food and Drug Administration; IDSA, Infectious Disease Society of America; NP, nasopharyngeal; WHO, World Health Organization.
¹ Not waived by Clinical Laboratory Improvement Amendments.
² Not immunochromatographic assay.

Assays that characterize a host response (such as C-reactive protein and procalcitonin) show promise in limiting unnecessary antibiotic use in certain clinical settings. However, their use and interpretation are complicated and can be confusing in the setting of returning travelers with potentially severe, nonbacterial tropical infectious diseases such as malaria and dengue.

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