How do hantavirus symptoms differ from the flu?

Early hantavirus and flu symptoms overlap: both cause fever, fatigue, muscle aches, and headache. CDC clinical sources note four differentiators. (1) Hantavirus muscle pain is severe and concentrates in large muscle groups (thighs, hips, lower back); flu pain is more diffuse. (2) Hantavirus rarely causes upper respiratory symptoms early on (no runny nose, sore throat); flu commonly does. (3) Hantavirus progresses to rapid respiratory deterioration 4-10 days after onset (HPS phase) — a hallmark not seen in flu. (4) Hantavirus has no seasonal pattern; flu peaks in winter. CDC clinical guidance specifies that a history of rodent exposure or travel to an endemic region is the key information that triggers consideration of hantavirus testing.