Hantavirus Symptoms: What to Expect

HPS — also called Hantavirus Cardiopulmonary Syndrome (HCPS) — is the form of hantavirus found in North and South America. It is caused primarily by Sin Nombre virus (carried by deer mice) in the U.S. and Andes virus in South America. The figure most often quoted for how deadly it is, 38%, is CDC's: "thirty-eight percent of people who develop respiratory symptoms may die from the disease." That number has a specific denominator, and the section below sets out which figure applies to whom — because CDC publishes three different fatality rates for this disease and they are not interchangeable.

Symptom Timeline

HPS vs. Flu — Key Differences

How Deadly Is Hantavirus? Three Numbers, Three Denominators

"Hantavirus death rate" is the most common search about this disease, and the answer depends entirely on who is counted in the denominator. CDC itself publishes three figures on three different pages — all correct, all describing different populations.

Is HPS becoming less deadly? By five-year block, our tabulation of CDC's case file gives 40.9% (1993–97), 30.1% (1998–2002), 32.7% (2003–07), 39.2% (2008–12), 32.9% (2013–17) and 25.8% (2018–22). The direction is downward but the series is noisy, and the blocks hold only 89 to 162 cases each, so swings of several points are expected from chance alone. CDC's own analysis of 1993–2009 found "no trends suggesting increasing or decreasing case counts or fatality rates" (MacNeil et al., Emerg Infect Dis 2011). We are not claiming an improvement — we are showing the series so the size of the noise is visible.

Hantavirus Death Rate by Age — and What Actually Predicts Death

Intuition says a disease this severe must kill the old and spare the young. For HPS the published data says otherwise. CDC's registry analysis of 510 cases from 1993 to 2009 broke the case-fatality rate down by age and found very nearly a flat line.

Across every band from adolescence to old age the fatality rate sits between a third and 37 per cent, and the statistical test for a difference between groups is as close to null as it gets (p = 0.992). The same paper found no significant difference by sex (33% in men, 39% in women, p = 0.18), by race or ethnicity (p = 0.284 and 0.637), or by region of the country (Southwest 34%, Northwest 35%, Midwest 39%, East 43%, p = 0.773). HPS does not spare healthy young adults. CDC's clinician brief says it plainly: "even healthy individuals are at risk." The under-10 row rests on five children and should not be read as a real difference.

What does predict death is how the illness is going, not who has it. From the same 510-case registry:

Two things follow. Fever and a low platelet count are near-universal in HPS and therefore say nothing about prognosis — but how far the platelets fall, and whether the blood is concentrating and the kidneys are straining, does. CDC's clinician brief adds two bedside thresholds that mark a poor outlook: a plasma lactate above 4.0 mmol/L, or a cardiac index below 2.2 L/min/m². And the timing is unforgiving: in CDC's registry the mean interval from symptom onset to death was 6.4 days (median 5), and without adequate treatment most deaths occur within 24 to 48 hours of the cardiopulmonary phase beginning.

The First Case Series — and Why the Early Numbers Were Worse

The disease was described in April 1994 from the first 17 confirmed patients of the Four Corners outbreak (Duchin et al., N Engl J Med). Their mean age was 32; fever and myalgia were universal, cough or breathlessness in 76%, gastrointestinal symptoms in 76%, headache in 71%; rapidly progressive pulmonary oedema developed in 15 of the 17, and 13 died — a 76% case-fatality rate. That figure is sometimes still quoted as "the" hantavirus death rate. It should not be. It describes the first weeks of an unrecognised disease, before anyone knew to look for it early, before the diagnostic test existed, and before the supportive-care approach now used was worked out. Three decades of surveillance put the real figure at roughly a third — which is still, by any standard, extremely high.

Symptom Frequency: What the Case Series Actually Record

Symptom lists are usually published without numbers. These are the numbers, from three independent sources — and note that the American series and the South American ones differ in what they emphasise.

The consistent signal across all three is the pairing of fever with severe muscle pain, with respiratory symptoms arriving later — which is precisely what makes early HPS look like influenza and precisely why the exposure history matters more than the symptom list. CDC's own summary is that about half of HPS patients also get headache, dizziness, chills and abdominal symptoms, and that the late symptoms appear four to ten days after the illness begins.