Identification of influenza A virus by shell vial culture and two commercially available antigen detection methods.
BACKGROUND
Influenza continues to be a major cause of morbidity and mortality especially in the elderly and persons with underlying disease. Shell vial cell culture and antigen detection techniques may speed up diagnosis and enable better patient treatment and management.


OBJECTIVE
To compare shell vial centrifugation culture with commercially available direct fluorescence and enzyme immunoassay kits using a variety of respiratory specimens.


METHODS
To detect influenza A virus, we compared direct fluorescent antibody (DFA) staining using the Bartels Viral Respiratory Panel and the Directigen FLU-A enzyme immunoassay (EIA) with shell vial centrifugation culture. Ninety-seven fresh specimens from a variety of respiratory sources, and transported from hospitals throughout the U.S. to our national referral laboratory, were tested.


RESULTS
Fifteen specimens were true positives: culture positive or both antigen tests positive. Sensitivity with culture was 93%, EIA 67%, and DFA 47%. Specificity was excellent with all three methods: 100%, 98%, 99%. Culture detected additional viruses that can cause respiratory tract disease: herpes simplex, cytomegalovirus, respiratory syncytial, influenza B, and adenovirus. Fourteen (70%) of 20 frozen specimens previously positive for influenza A were positive on retest by EIA. Overall sensitivity of EIA compared with culture using 35 positive specimens was 69%.


CONCLUSIONS
The rapid EIA is useful to screen for influenza A, but critical antigen-negative specimens should be submitted to a virology laboratory for culture. Shell vial cultures can provide a sensitive and universal diagnostic system for influenza A and a variety of other viruses.
Steed
L L
LL
Diagnostic Virology Laboratory, Associated Regional and University Pathologists, Inc., Salt Lake City, UT 84108, USA.
Salmon
V C
VC
Overall
J C
JC