Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/30/2007
Publication Date: 7/1/2007
Citation: Elvinger, F., Akey, B., Senne, D.A., Pierson, F., Porter-Spalding, B., Spackman, E., Suarez, D.L. 2007. Characteristics of diagnostic tests used in the 2002 low pathogenicity avian influenza H7N2 outbreak in Virginia. Journal of Veterinary Diagnostic Investigation. 19(4):341-348. Interpretive Summary: During 2002 an outbreak of low pathogenic H7N2 avian influenza virus (AIV) occurred in Virginia, North Carolina and West Virginia. During this outbreak two new diagnostic methods, real-time RT-PCR and a commercial virus detection kit were employed because of their rapid formats as compared to the standard method of virus detection, virus isolation. In this report, the two new methods are statistically compared with virus isolation and with each other to evaluate their performance as diagnostic tests for AIV. The conclusions are that the real-time RT-PCR test is highly sensitive and specific and that it could be useful for rapid and sensitive AIV detection. Additionally, although the virus detection kit is much less sensitive than either virus isolation or real-time RT-PCR, when applied properly its speed and portability could assist in controlling an AIV outbreak. The specific considerations for the implementation of each test in future outbreaks are also discussed.
Technical Abstract: An outbreak of low pathogenicity avian influenza (LPAI) H7N2 occurred in 2002 in the Shenandoah Valley, Virginia, a high density poultry production region. A combination of clinical signs, and laboratory diagnostic tests designed to detect avian influenza (AI) antibodies, virus, or H7 specific RNA were used to identify infected flocks. In this report fitness for purpose of three virus/RNA detection assays used during the outbreak is examined: antigen capture enzyme immunoassay (AC-EIA), real-time reverse transcription - polymerase chain reaction (RRT-PCR) and virus isolation (VI). Results from testing 762 turkey and 2,216 chicken tracheal swab specimens were analyzed to determine diagnostic sensitivities and specificities of these tests under field conditions using Bayesian techniques for validation of diagnostic tests in the absence of a “gold standard.” Diagnostic sensitivities of the AC-EIA, RRT-PCR and VI [with 95% probability intervals] were 65.9[50.6;81.3]%, 85.1[71.9;95.7]%, and 92.9[78.0;98.8]% (in reference to AC-EIA) or 88.7[76.0;97.2]% (in reference to RRT-PCR), in turkeys, and 75.1[45.6;94.2]%, 86.3[65.9;97.1]%, and 86.2[65.8;97.1]% or 86.3[66.4;97.2]% in chickens. Specificities were 99.1[97.9;99.8]%, 98.9[98.0;99.5]% and 98.6[97.4;99.4]% or 98.8[97.8;99.5]%, in turkeys and between 99.25% and 99.27% with probability intervals of about 0.4% for all tests in chickens. Simultaneous use of AC-EIA and RRT-PCR tests contributed significantly to the rapid control of the outbreak. However, the AI RRT-PCR assay, with its high sensitivity and specificity, combined with relatively low cost and fast turnaround, could be used as the sole diagnostic test in outbreaks of LPAI.