Hantavirus pulmonary syndrome (HPS) has a case fatality rate of 36%, according to CDC surveillance data covering all confirmed US cases since 1993. That makes it one of the deadliest infectious diseases you can encounter in North America. There is no vaccine. There is no specific antiviral treatment. And the most common way people get infected is by sweeping out a dusty shed.

What is hantavirus?

Hantaviruses belong to the family Hantaviridae, a group of RNA viruses carried by rodents worldwide. Different rodent species carry different hantavirus strains, and the disease they cause varies by region.

In the Americas, the primary concern is Sin Nombre virus (SNV), first identified during a 1993 outbreak in the Four Corners region where Arizona, Colorado, New Mexico, and Utah meet. That outbreak killed 13 of 24 confirmed patients and put hantavirus on the public health map in the United States. Sin Nombre virus causes HPS, which attacks the lungs and can progress from mild flu-like symptoms to fatal respiratory failure in a matter of days.

In Europe and Asia, different hantavirus strains (Hantaan, Puumala, Seoul, and Dobrava viruses) cause hemorrhagic fever with renal syndrome (HFRS), which primarily damages the kidneys. HFRS tends to have a lower fatality rate, roughly 1-15% depending on the strain, but affects far more people globally. China alone reports 20,000-50,000 HFRS cases annually.

How does it spread?

The primary reservoir for Sin Nombre virus in North America is the deer mouse (Peromyscus maniculatus), one of the most common rodents on the continent. Deer mice range across nearly all of the US and Canada except the Southeast and far eastern seaboard. They readily colonize human structures, especially those left unoccupied for periods of time: cabins, sheds, barns, storage buildings, and garages.

Infected deer mice shed the virus in their urine, droppings, and saliva. The virus can remain infectious in dried rodent waste for several days under the right conditions. The primary transmission route is inhalation. When someone disturbs dried droppings or nesting material - by sweeping, vacuuming, or simply walking through an infested space - tiny particles become airborne. Breathing those particles in is enough to cause infection.

This is a zoonotic disease with an important distinction: in the Americas, hantaviruses do not spread from person to person. There has never been a documented case of human-to-human transmission of Sin Nombre virus. This means hantavirus cannot cause a pandemic, but it remains a persistent, deadly threat to individuals who encounter rodent-contaminated environments. In South America, one strain (Andes virus) has shown limited person-to-person spread, but this is the exception.

Who gets infected?

Since 1993, the CDC has recorded approximately 850 confirmed HPS cases in the United States, averaging 20-30 cases per year. The true number is likely higher because mild cases may go undiagnosed. About one in three confirmed patients dies.

Cases cluster in rural and periurban areas of western states. New Mexico, Colorado, Arizona, California, Washington, and Montana report the most cases. The typical patient is someone who encountered rodent droppings during cleaning, construction, or outdoor activities. Cabin owners opening up seasonal properties are at particular risk. So are hikers sleeping in backcountry shelters, agricultural workers in barns and grain storage, and anyone cleaning out a rodent-infested space.

Outbreaks tend to spike following wet winters and springs, which increase rodent food supplies and boost deer mouse populations. The 2012 outbreak at Yosemite National Park infected 10 visitors staying in signature tent cabins where deer mice had colonized the insulation. Three of those visitors died.

Symptoms and progression

HPS typically progresses through two phases. The first phase begins 1-5 weeks after exposure with non-specific symptoms: fever, muscle aches, fatigue, headache, and sometimes nausea and abdominal pain. This phase lasts 2-5 days and is nearly impossible to distinguish from the flu without specific testing.

The second phase arrives abruptly. Within hours, patients develop a cough, shortness of breath, and rapidly worsening respiratory distress as their lungs fill with fluid. This pulmonary edema can progress to complete respiratory failure within 24-48 hours. Patients who survive the first 48 hours of respiratory distress generally recover, but they may need mechanical ventilation and intensive care to get through it.

Early recognition matters. If you develop fever and respiratory symptoms within 6 weeks of exposure to rodent droppings or nesting material, tell your doctor about the exposure immediately. Early supportive care in an ICU setting improves survival rates significantly.

Prevention

There is no hantavirus vaccine approved for human use, and ribavirin (an antiviral sometimes used for other hantavirus infections) has not shown clear benefit for HPS. Prevention comes down to avoiding exposure to rodent waste and keeping rodents out of living spaces.

Cleaning rodent-infested spaces safely. Never sweep or vacuum rodent droppings. This is the single most important rule. Sweeping and vacuuming launch particles into the air at exactly the concentration that causes infection. Instead, ventilate the space by opening doors and windows for at least 30 minutes before entering. Then spray droppings and nesting material with a solution of 1 part household bleach to 10 parts water. Let it soak for 5-10 minutes. Wipe up the wet material with paper towels or rags and dispose of them in sealed plastic bags. Wear rubber gloves throughout. If the infestation is heavy, wear an N95 respirator.

Rodent-proofing your home. Seal any opening larger than 6mm (about the width of a pencil) with steel wool, caulk, or metal flashing. Deer mice can squeeze through remarkably small gaps. Store food (including pet food and birdseed) in sealed metal or thick plastic containers. Clear brush and debris within 30 meters of your home. Don't stack firewood against the house.

Camping and outdoor precautions. Don't sleep in structures with visible rodent droppings. Air out cabins before using them. Store food in rodent-proof containers. Don't set up camp near rodent burrows or woodpiles.

These are straightforward infection prevention steps that cost almost nothing. The gap between knowing them and not knowing them is the gap between a routine cabin opening and a life-threatening infection. For broader strategies on keeping your household ready for health threats, see our outbreak preparedness supplies guide.