Influenza surveillance in Pennsylvania.
D000041:Absenteeism; D004196:Disease Outbreaks; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology*; D009787:Occupational Medicine; D009975:Orthomyxoviridae / Q000302:isolation & purification; D010414:Pennsylvania; D011159:Population Surveillance; D011635:Public Health Administration; D012572:School Health Services