Usefulness of Influenza Rapid Antigen Test in Influenza A (H1N1)

Purpose : The aim of this study was to examine the sensitivity and specificity of the influenza rapid antigen test, in comparison with reverse transcription polymerase chain reaction (RT-PCR), according to the time of the test from symptom onset and the clinical manifestations in the patients tested for suspected infection of the influenza A (H1N1) at a second hospital. Methods : A total of 529 pediatric patients, aged between 6 and 12 years old, who visited the emergency department from October 1, 2009 to December 31, 2009, received the influenza rapid antigen test and RT-PCR. We examined the sensitivity and specificity of the influenza rapid antigen test in comparison with RT-PCR according to the time of the test from symptom onset (˂24 hours, 24 to 48 hours, 48 to 72 hours, ˃72 hours) and clinical manifestations (fever, cough, rhinorrhea·nasal obstruction, sore throat, gastrointestinal symptoms, and general symptoms) in a retrospective study based on hospital charts. Results : The sensitivity of the influenza rapid antigen test at elapsed times of less than 24 hours, 24 to 48 hours, and 48 to 72 hours after the onset of the symptoms was 53.9%, 61.4%, and 62.1% respectively. When the elapse time was greater than 72 hours, the sensitivity was 31.6%; thus, the sensitivity of the influenza rapid antigen test tended to decrease with elapsed time. The sensitivity of the test was 79% in patients presenting with gastrointestinal symptoms, which was the highest, but there was no statistical difference according to the clinical manifestations of the patients. Conclusions : Our study suggests that more accurate results might be gained when the influenza rapid antigen test is performed within 72 hours after symptom onset. [Pediatr Allergy Respir Dis(Korea) 2012;22:71-77]