In a small number of recruiting sites at defined periods during the main study we will use an alternative rapid diagnostic test, namely the HX Diagnostics Influenza A+B test (HX Diagnostics, San Francisco, CA) which is based on 3rd generation lateral flow immunoassay technology and may be more sensitive and specific than the QuickVue test. In this case, subjects with a positive result on the HX Diagnostics Influenza A+B test would be eligible for further follow up as described above. We will calculate the sensitivity and specificity of the rapid diagnostic test in our study setting, using viral culture or PCR of a nose and throat swab as the gold standard. See also 7(c).