Hantavirus: What You Need to Know Before You Clean Out the Garage

Most people have heard of hantavirus but assume it's a remote wilderness disease that doesn't apply to their lives. That assumption is wrong in ways that matter. The deer mouse — the primary carrier of Sin Nombre virus, the hantavirus strain responsible for most U.S. cases — lives throughout the continental United States, including suburban and semi-rural areas. It commonly nests in garages, sheds, woodpiles, attics, and rarely-opened storage areas. You don't have to be hiking in Yosemite to be exposed. You have to sweep somewhere a mouse has been.

What Hantavirus Is

Hantavirus Pulmonary Syndrome (HPS) is a severe respiratory illness caused by hantaviruses — a group of viruses carried by certain rodent species. In North America, the primary carrier is the deer mouse (Peromyscus maniculatus), a small brown-and-white rodent found across most of the continent. Infected deer mice shed the virus in their droppings, urine, and saliva. The virus can remain viable in dried material for days.

Transmission to humans happens almost exclusively through inhalation. When dried rodent droppings or nesting material is disturbed — swept, vacuumed, moved — virus particles become airborne and are inhaled. Direct contact with a live or dead mouse is a much less common route. Person-to-person transmission of the North American strains does not occur.

The fatality rate for HPS is approximately 35–38 percent, according to the CDC. That figure has held relatively stable for decades despite improvements in critical care. The reason is that the disease, once it enters its severe phase, progresses extremely rapidly — often within hours — and there is no specific antiviral treatment. Supportive care in an intensive care unit is the only intervention available. Early recognition and immediate hospitalization are what save lives.

Who Is Most at Risk

Anyone who disturbs rodent-contaminated material is at risk. But certain activities and circumstances create much higher exposure likelihood:

• Opening structures after seasonal closure — cabins, vacation homes, sheds, barns, or garages that have been sealed or minimally used through winter. Mice seek shelter in cold months; spring opening can disturb accumulated nesting material.
• Cleaning or reorganizing storage areas — particularly attics, basements, and garages where boxes or items haven't been moved in months or years.
• Agricultural and outdoor work — plowing fields, moving hay bales, working in grain storage areas, or handling wood piles where rodents nest.
• Pest cleanup — removing visible rodent droppings or nesting material without proper precautions is among the highest-risk activities.
• Camping and hiking — sleeping in areas with rodent activity, particularly in enclosed shelters, increases risk.

There is no evidence that age increases susceptibility to the virus itself. However, older adults may be at greater risk of severe outcomes once infected because underlying cardiovascular or respiratory conditions reduce the margin the body has to tolerate the fluid accumulation in the lungs that characterizes the severe phase of HPS. The disease attacks the lungs' ability to oxygenate blood — any pre-existing limitation in cardiorespiratory reserve matters.

Recognizing the Symptoms

HPS unfolds in two phases that are easy to misinterpret as an ordinary illness followed by a sudden, unexpected deterioration.

The early phase (days 1–5): Symptoms are flu-like and nonspecific — fatigue, fever, muscle aches (particularly in the thighs, hips, and back), headache, dizziness, and sometimes nausea, vomiting, or diarrhea. There is typically no cough or runny nose at this stage. This phase is almost indistinguishable from flu or a common viral illness, which is exactly why it gets mismanaged. People feel sick but not alarmed.

The cardiopulmonary phase (days 4–10): This is where the disease becomes life-threatening, and it can arrive with very little warning. Coughing begins. Shortness of breath develops rapidly. Fluid fills the lungs (pulmonary edema) and blood pressure drops. Patients who seemed stable can deteriorate to respiratory failure within hours. This phase requires intensive care — mechanical ventilation and in severe cases ECMO (extracorporeal membrane oxygenation) to support oxygenation while the lungs recover.

The critical window is the transition between phases. The CDC notes that people who survive HPS generally do so because they were already hospitalized and being monitored when the cardiopulmonary phase began, not because they drove themselves to the ER when they felt they couldn't breathe.

If you have had any potential rodent exposure in the past 1–8 weeks and develop fever, severe muscle aches, and fatigue with no other obvious explanation, tell your doctor about the exposure specifically and explicitly. HPS is rare enough that clinicians in non-endemic areas may not immediately consider it without a prompted history. The incubation period ranges from 1 to 8 weeks, with most cases presenting within 2–4 weeks of exposure.

Prevention: What the CDC Actually Recommends

The good news is that prevention is highly effective. The exposure events that lead to HPS are almost always avoidable with proper precautions. The following guidance is adapted from CDC recommendations:

Before cleaning any potentially contaminated space:

• Open windows and doors and allow the space to ventilate for at least 30 minutes before entering. Leave during this ventilation period.
• Wear rubber, latex, or vinyl gloves. Wear an N95 respirator or better — a standard dust mask does not filter particles small enough to block hantavirus-contaminated aerosols. Surgical masks are also insufficient.
• Do not sweep or vacuum dry droppings. Sweeping aerosolizes the material. Dry vacuuming does the same.

The correct cleaning method for rodent droppings:

• Spray droppings, nesting material, and contaminated surfaces with a disinfectant solution (a 10 percent bleach solution — roughly 1.5 cups of bleach per gallon of water — or an EPA-registered disinfectant) and let it soak for 5 minutes before wiping up. The wet method prevents aerosolization.
• Use paper towels to wipe up the material, place in a plastic bag, seal it, and double-bag before disposal.
• Mop floors rather than sweeping after the initial disinfectant cleanup.
• After cleanup, remove gloves carefully to avoid contact with the outer surface. Wash hands thoroughly with soap and water.

Ongoing rodent control:

• Seal entry points into your home — mice can fit through openings the diameter of a pencil (approximately 6mm). Steel wool and caulk are effective short-term; hardware cloth or metal sheeting for permanent sealing.
• Store food (including pet food) in rodent-proof containers.
• Remove woodpiles, debris, and clutter within 100 feet of your home — these are preferred nesting sites.
• Snap traps are more reliable than glue traps for control; use them along walls and in corners where mice travel.

Current Situation in the U.S.

HPS is not a new disease — the Sin Nombre virus was identified after a cluster of cases in the Four Corners region of the Southwest in 1993 — but cases occur every year across the United States. The CDC has recorded approximately 850 cases since 1993, with roughly 36 percent resulting in death. Cases have been reported in 34 states; the highest concentrations are in the western United States, but no region is entirely without risk where deer mice are present.

Case counts fluctuate with rodent population cycles, which are themselves driven by food supply — particularly acorn and seed production. Years with abundant food production drive rodent population spikes the following year, which increases human exposure risk. The disease is not reportable in all states, so CDC figures likely undercount actual incidence.

There is currently no vaccine for hantavirus in the United States (a vaccine is used in parts of Asia for different hantavirus strains). Prevention remains the only tool.

The Bottom Line

This is a disease that kills roughly one in three people it infects, has no specific treatment, and is almost entirely preventable through a set of straightforward precautions that most people simply don't know to take because they've never been told. The tasks that create exposure — cleaning out a shed, opening a cabin, moving old boxes — are so ordinary that the idea of taking precautions doesn't occur to people. That's exactly the problem.

If you live in or near a rural or semi-rural area, have a garage, shed, or outbuilding, or regularly open structures that have been closed through winter: get an N95, buy a jug of bleach, and use the wet-wipe method instead of the broom. The precautions take five minutes to set up. The disease they prevent does not.