Table 3 Key Variables and Sources of Information for Hospitalized and Non-Ill Infants
| Â | Hospitalized Infants | Non-Ill Infants | ||
|---|---|---|---|---|
Enrollment | 3–5 Week Follow-Up | Hospital Records | Enrollment | |
Specimens | ||||
 Combined nasal and oropharyngeal swabs | √ |  |  | √ |
 Blood (Sera) | √ | √ |  |  |
 Endotracheal aspirate (for intubated infants) | √ |  |  |  |
Infant illness | ||||
 Date of illness onset and resolution | √ | √ |  |  |
 Maternal-reported symptoms | √ | √ |  |  |
 Ambulatory and self-care for illness | √ | √ |  |  |
 Clinical signs at admission and per day |  |  | √ |  |
 Clinical diagnoses |  |  | √ |  |
 Clinical interventions |  |  | √ |  |
 Clinical laboratory results |  |  | √ |  |
 Clinical radiographic information |  |  | √ |  |
 Readmission to hospital |  | √ | √ |  |
 Other hospitalizations post-discharge |  | √ | √ |  |
Infant characteristics | ||||
 Demographic (sex, birth date, race, ethnicity) information | √ |  |  | √ |
 Current weight | √ | √ | √ | √ |
 Current length | √ | √ | √ | √ |
 Perceived overall health and functioning | √ | √ |  | √ |
 Influenza vaccination status (from vaccination cards when available) | √ | √ | √ | √ |
 Delivery characteristics (including gestational age, birth weight, complications and abnormalities) | √ |  | √ | √ |
 Diagnoses and history of care for chronic conditions | √ |  | √ | √ |
 Diagnoses and history of care for prior acute illnesses | √ |  | √ | √ |
 Results of previous laboratory tests |  |  | √ |  |
 Other immunization status | √ | √ | √ | √ |
 Daycare attendance | √ |  |  | √ |
Household characteristics | ||||
 Age of each household member | √ |  |  | √ |
 Education and occupation of parents (or guardians) | √ |  |  | √ |
 House size and number of rooms | √ |  |  | √ |
 Subjective social status | √ |  |  | √ |
 Household wealth index | √ |  |  | √ |
 Household smoking | √ |  |  | √ |
Maternal characteristics | ||||
 Subjective health status | √ | √ |  | √ |
 Medical conditions | √ |  |  | √ |
 Pregnancy history and complications during study infant’s gestation | √ |  |  | √ |
 History of and current breastfeeding | √ |  |  | √ |
 Influenza vaccination status (from vaccination cards when available) | √ | √ | √ | √ |
 Knowledge of and worry about influenza illness |  | √ |  | √ |
 Knowledge of and attitudes toward influenza vaccine for infants aged ≥6 months |  | √ |  | √ |