Performance of influenza rapid point-of-care tests in the detection of swine lineage A(H1N1) influenza viruses

Abstract

Background: In April 2009, an A(H1N1) influenza virus of swine lineage was detected in humans in the USA, and in just over a month has infected over 10,000 people in more than 40 countries.

Objectives: To determine the performance of the Binax Now, BD Directigen EZ, and the Quidel QuickVue influenza rapid point-of-care (POC) tests for the detection of the recently emerged swine lineage A(H1N1) virus.

Methods: Swine lineage A(H1N1) and human seasonal influenza strains were cultured and then diluted to specific infectivity titres. Viral dilutions were assayed by the rapid POC tests and by real-time RT-PCR.

Results: All three of the rapid POC tests successfully detected the swine lineage A(H1N1) viruses at levels between 10(3) and 10(5) TCID(50)/ml (tissue culture infectious dose(50)), with the BD Directigen test demonstrating marginally greater sensitivity than the other two tests. Viral infectivity and RNA load data for viruses at the detection limit of the rapid test kits, suggested that both the Quidel and the Binax tests were less sensitive for the detection of swine lineage A(H1N1) viruses than for human seasonal strains. In comparison the BD Directigen demonstrated similar sensitivity when detecting swine lineage A(H1N1) and human seasonal viruses.

Conclusions: The three rapid POC tests all detected the emergent swine lineage A(H1N1) virus when it was present at high virus concentrations. Early diagnosis of infection can assist in the rapid treatment. However the tests are significantly less sensitive than PCR assays and as such, negative results should be verified by a laboratory test.

Figure 1

Comparison of the sensitivity of rapid point‐of‐care (POC) tests with viral RNA levels in swine lineage A(H1N1) virus‐positive clinical specimens. Mean cycle threshold (Ct) values ± standard deviations were derived from the Ct values determined by real‐time RT‐PCR for either the three swine lineage viruses or the three human seasonal strains at the detection limit for the respective rapid POC test. Circles indicate the Ct values (derived from the same influenza A matrix real‐time RT‐PCR assay as used for the other experiment) for 10 different clinical specimens that were swine lineage A(H1N1) virus‐positive.