Identification of influenza A virus by shell vial culture and two commercially available antigen detection methods.
BACKGROUND
Effective use of amantidine and rimantidine for treating patients and for reducing transmission requires rapid diagnosis of influenza A. Rapid culture methods require 1-2 days to detect influenza A virus. Direct fluorescent antibody (DFA) staining and enzyme immunoassay (EIA) can detect influenza A antigen within 1-4 h.


OBJECTIVE
We compared DFA staining using the Bartels viral respiratory panel and the Directigen FLU-A EIA with shell vial centrifugation culture.


METHODS
Ninety-seven fresh specimens from a variety of respiratory sources and transported from hospitals throughout the USA to our national referral laboratory were tested. A true positive was defined as culture positive or both antigen tests positive.


RESULTS
Fifteen specimens were true 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
These results suggest that the rapid EIA is useful to screen for influenza A, but that critical antigen-negative specimens should be submitted to a virology laboratory for culture for optimal sensitivity and for recovery of other viruses.
Steed
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LL
Diagnostic Virology Laboratory, Associated Regional and University Pathologists, Inc., Salt Lake City, UT 84108, USA.
Salmon
V C
VC
Overall
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JC