Japanese Journal of Infectious Diseases, Vol.65(2) : 105~110, 2012
Public health authorities recommend that isolation precautions for influenza should be continued for 7 days after illness onset or until 24 h after the resolution of symptoms, whichever event lasts longer. However, little data are available regarding the duration of isolation for patients with 2009 pandemic H1N1 (pH1N1). We recruited patients with confirmed pH1N1 virus infection at a 2,000-bed tertiary care center. Influenza viral loads from oropharyngeal swab specimens were serially determined by reverse transcriptase quantitative polymerase chain reaction every other day, and the risk factors for prolonged viral shedding were investigated. To evaluate the current recommendations for isolation precautions, we measured the intervals between symptom onset and the last viral RNA detection, and that between the last viral RNA detection and the point at which the patient was symptom-free for 24 h. From November 2009 to January 2010, 26 patients were enrolled, and viral RNA was detected in more than half of the eligible patients (10 of 19, 52.6%) for ≥7 days after symptom onset. While evaluating the policy for lifting quarantine, we found that viral RNA was detected in 4 of 15 patients (26.7%) beyond the recommended duration of isolation. In conclusion, viral RNA was detected in a substantial proportion of hospitalized patients even when they fulfilled the recommended conditions for lifting quarantine, and we believe that more prudence is required in this aspect.