The purpose of this study is to determine whether nonpharmaceutical interventions (i.e., handwashing and masks) reduce secondary transmission of influenza in households.

HITS is a multi-year project that will prospectively identify laboratory-confirmed influenza infected children. Secondary influenza infection will then be examined among members of the child's household and effectiveness of non-pharmaceutical interventions to decrease secondary infection will be assessed. The pediatric influenza-infected index case will be identified by rapid influenza testing and their household will then be enrolled and randomized to one of three study arms: control, hand washing (Intervention 1), and hand washing and mask use (Intervention 2). Following enrollment, at days 0, 3 and 7, all household participants will be tested: the index case will be assessed for influenza viral shedding and household members will be assessed for secondary influenza infection. This study is being conducted at Queen Sirikit Institute for Child Health in Bangkok.

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.