Objective: Evaluate the performance of clinical data and the rapid influenza diagnostic test (RIDT) in diagnosing influenza H1N1, and analyze the cost-benefit of using this diagnostic tool.
Methods: The RIDT was used for patients who came to four hospitals in Mexico City with an influenza-like illness (ILI) in October and November 2009. The diagnostic performance of the ILI clinical data and the RIDT was compared to that of the real-time reverse transcription polymerase chain reaction (rRT-PCR) test. The rRT-PCR test was conducted in a reference laboratory and blinded to the results of the RIDT. An economic evaluation also was conducted to estimate the budgetary impact of using the RIDT.
Results: The study included 78 patients, 39 of whom tested positive for influenza H1N1 and 6 tested positive for seasonal influenza A, according to the results of the rRT-PCR. The ILI clinical data yielded a sensitivity of 96% and specificity of 21%; the RIDT yielded a sensitivity of 76% and specificity of 82%; and the ILI clinical data and RIDT together yielded a sensitivity of 96% and specificity of 100%. The positive likelihood quotient for ILI-headaches was 31.5 and that of ILI-odynophagia, 330. The use of RIDT yielded savings of US$12.6 per each suspected case.
Conclusions: Use of the RIDT to aid in the diagnosis of influenza H1N1 increases certainty and lowers the average cost per suspected and infected patient.