Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1411 page)

   Nasopharyngeal wash specimens, or swabs, are usually associated with the best sensitivity of culture.

   Specimens are typically inoculated onto several different types of cell lines to help ensure growth of all of the target pathogens. Shell vial cultures may be inoculated in addition to tube cultures. Positive cultures are determined by cytopathic effect or by staining with virus-specific tagged monoclonal antibodies.

   
Turnaround time

   Shell vial cultures may be positive within 48–72 hours.

   Most respiratory viral pathogens can be detected in tube cultures by blind staining with immunologic reagents after 7 days of inoculation.

   Interpretation

   
Expected results:
Negative.

   
Positive results:
Positive cultures for specific viruses indicate active infection with that agent.

   
Negative results:
Negative viral culture significantly decreases the possibility but does not rule out respiratory virus infection. Molecular diagnostic techniques should be considered in patients with severe disease.

   Limitations

   Negative cultures may be caused by numerous factors, including poor specimen collection technique, collection of specimens after acute disease when virus concentrations are below the level of detection, or infection caused by a viral pathogen not included in the respiratory virus culture panel used.

   Coinfection with two or more respiratory viral pathogens is relatively common. The impact of coinfection with specific viral pathogens, such as human metapneumovirus, awaits further study.

RESPIRATORY VIRUS DIRECT DETECTION BY ENZYME IMMUNOASSAY (EIA) AND DIRECT FLUORESCENT ANTIBODY (DFA) TESTS

   Definition