Once enrolled, study procedures will consist of: collection of nasal swabs and fluid, stool specimens, and optional throat swabs, at enrollment visit (first week of life), 3-5 weeks of age (Visit 2), 3-5 months (Visit 3), and 12 months +/- 2 months (Visit 4); blood draw at Visits 3 and 4; spirometry will be performed at Visits 2, 3 and 4: non-sedated infant pulmonary function tests will be conducted at all visits for all cohorts; at Visits 3 and 4, sedated infant pulmonary function tests are optional for Cohorts 1 and 2 only. Finally, surveys will be completed about every two months starting at about two months, then four weeks after Visit 3, and about every 8 weeks until Visit 4, to review infection history, medication (including antibiotics) history and wheezing history.