Household Influenza Transmission Study

Inclusion Criteria: * Child, 1 month through 15 years of age * Resident of Bangkok Metropolitan Area * Outpatient of Queen Sirikit National Institute of Child Health Children's * Hospital seen during HITS' active study period * Positive influenza rapid test result from patient presenting with influenza-like illness * In addition to the index case, consent must be obtained from at least 2 household members ≥1 month of age who plan to sleep inside the house for a period of at least 21 days from the time of enrollment Exclusion Criteria: * Illness onset 48 hours or more before presentation and influenza testing at Queen Sirikit National Institute of Child Health Children's Hospital * Treatment with influenza antiviral medications since it may decrease secondary attack rate * Children who are at high risk for severe influenza disease (e.g., chronic lung disease, renal disease, chemotherapy for cancer, long-term aspirin therapy) * A history of influenza-like illness in another household member that precedes the index case by 7 days or less will lead to exclusion of the household because the source of influenza infection for secondary cases is uncertain. * Receipt of influenza vaccine by any household member during the preceding 12 months. * Prior participation in HITS.