A 6-mоnth-оld infаnt is brоught to the clinic with nаsаl congestion, rhinorrhea, and coughing of 2 days' duration. The parents report that the infant is becoming increasingly irritable, breathing faster, and sleeping poorly. The infant has been in day care for 5 weeks. There are no smokers in the home, both parents have had colds during the past couple of weeks, and the child's mother has a history of childhood asthma. The infant has no history of cardiopulmonary disease, prematurity, or immunodeficiency. Immunizations are up to date. Physical Examination: Temperature 38°C (rectal); pulse 120, respirations 42 General appearance: Alert, with harsh cough Skin: Warm and pink; good skin turgor; no rashes Head, ears, eyes, nose, throat: Anterior fontanel soft and flat; tympanic membranes clear, with all landmarks present bilaterally; moist mucus membranes; profuse, clear nasal discharge bilaterally; mild-to-moderate erythema of the pharynx; tonsils not enlarged and no exudates; harsh cough; no excessive drooling; Respiratory: Expiratory wheezes and crackles bilaterally; moderate intercostal retractions; mild nasal flaring Chest Radiography: Hyperinflation (depressed diaphragm) with mild interstitial infiltrates Which is the most likely diagnosis for this infant?