Influenza virus infections.
D000293:Adolescent; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D005194:Family Practice; D006761:Hospitals; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007251:Influenza, Human / Q000453:epidemiology; D009975:Orthomyxoviridae; D009976:Orthomyxoviridae Infections / Q000453:epidemiology; D012140:Respiratory Tract Diseases / Q000382:microbiology*