Hantaviruses in humans cause 2 syndromes: hantavirus pulmonary syndrome (HPS), a noncardiogenic pulmonary edema; and hemorrhagic fever with renal syndrome (HFRS) (see Hemorrhagic Fevers and Related Syndromes). The prodromal illness of HPS is 3 to 7 days and is characterized by fever; chills; headache; myalgia of the shoulders, lower back, and thighs; nausea; vomiting; diarrhea; dizziness; and sometimes cough. Respiratory tract symptoms or signs usually do not occur for the first 3 to 7 days until pulmonary edema and severe hypoxemia appear abruptly after the onset of cough and dyspnea, and then the disease progresses over a few hours. In severe cases, persistent hypotension caused by myocardial dysfunction is present.

The extensive bilateral interstitial and alveolar pulmonary edema and pleural effusions are the result of a diffuse pulmonary capillary leak and appear to be caused by immune responses to hantavirus in endothelial cells of the microvasculature. Intubation and assisted ventilation usually are required for only 2 to 4 days, with resolution heralded by the onset of diuresis and rapid clinical improvement.

The severe myocardial depression is different from that of septic shock; the cardiac indices and the stroke volume index are low, the pulmonary wedge pressure is normal, and systemic vascular resistance is increased. Poor prognostic indicators include persistent hypotension, marked hemoconcentration, a cardiac index of less than 2, and abrupt onset of lactic acidosis with a serum lactate concentration of greater than 4 mmol/L (36 mg/dL).

The mortality rate for patients with HPS in recent years has been 30% to 40%. Asymptomatic and mild forms of disease are rare in adults, but limited information suggests they may be more common in children. Serious sequelae are uncommon.