Given high seroprevalence rates in endemic areas, it appears that most people develop subclinical infections.

• After an incubation period of 4-8 days, pts develop fever (75-100%), myalgia (77%), headache (82%), and malaise (97%).
• Severe complications—respiratory distress, a toxic shock-like syndrome, and opportunistic infections—occur most often in elderly pts.
• On laboratory examination, pts are found to have leukopenia (55%), thrombocytopenia (75%), and elevated serum aminotransferase levels (83%).