Hantavirus Pulmonary Syndrome: Symptoms, Stages and Survival

Hantavirus pulmonary syndrome - HPS in North America, HCPS in South America where cardiovascular collapse features more prominently - is one of medicine's clearer staged illnesses. It moves in three phases, often over a single week, and recognising which phase a patient is in informs everything from triage to ventilator strategy.

Phase 1 - the prodrome (days 1 to 5)

The opening act is profoundly unspecific: fever, deep muscle aches in the large muscle groups (thighs, hips, back, shoulders), headache, fatigue. Around half of patients develop gastrointestinal symptoms - nausea, vomiting, abdominal pain, diarrhoea. There is usually no significant respiratory symptom in this phase, which is precisely why the diagnosis is missed.

Two clinical pearls separate hantavirus prodrome from ordinary influenza: profound thrombocytopenia (a sharp drop in platelet count) and an unusually high haematocrit (haemoconcentration as plasma leaks into the lungs). A clinician with a high index of suspicion can pick this up on a basic panel before the chest x-ray shows anything.

Phase 2 - the cardiopulmonary phase (days 4 to 10)

This is the cliff edge. The transition from prodrome to severe disease is often abrupt - sometimes a matter of hours. The triggering event is capillary leak in the pulmonary vasculature: fluid floods the alveoli, oxygenation collapses, and the patient develops non-cardiogenic pulmonary oedema.

Clinical features at this stage:

• Dyspnoea (shortness of breath) that progresses over hours, not days
• Tachycardia, often disproportionate to fever
• Hypotension; in HCPS specifically, frank cardiogenic shock
• Diffuse interstitial and alveolar infiltrates on chest imaging
• Severe hypoxaemia, often requiring intubation

Most deaths occur in this window. The 38% case-fatality rate that gets quoted refers, very specifically, to patients who have reached cardiopulmonary symptoms. Patients identified and supported before they reach this phase do considerably better.

Phase 3 - diuresis and convalescence (week 2 onwards)

Survivors of phase 2 enter a diuretic phase in which the body sheds the fluid it has accumulated, sometimes producing four to six litres of urine in a day. Oxygenation improves rapidly. Most patients are weaned off mechanical ventilation within a week of crossing into this phase.

Convalescence is slow. Fatigue, reduced exercise tolerance and patchy lung-function abnormalities can persist for months. Long-term outcomes are generally good - there is little evidence of permanent lung damage in the majority of survivors.

What treatment looks like

There is no approved antiviral specific to hantavirus. Care is meticulously supportive:

• Early recognition and transfer to an intensive care unit, ideally one with extracorporeal membrane oxygenation (ECMO) capability
• Cautious fluid management - overhydration in phase 2 is catastrophic
• Vasopressor support for the cardiogenic component
• ECMO has dramatically improved survival in the most severe HCPS cases, particularly in Chile

Why it gets missed

HPS hides inside influenza-like illness for several days. Clinicians outside endemic regions often have no reason to consider it. The MV Hondius outbreak is a useful reminder: in 2026, exposure history can include events that ended in another hemisphere weeks earlier.