You opened the attic. You saw the droppings. Now what.
Most people, right then, do one of three things. They grab a broom. They grab the shop-vac. Or they pull out a bottle of bleach and a paper towel and start wiping. All three are wrong. All three are how dust from a dead mouse gets into your lungs.
This is a practical guide for the 30 seconds after you find the problem. With hantavirus on every front page this week and the CDC just escalating its MV Hondius response to Level 3, more people are looking up the right answer at the wrong time. Here is what to actually do.
One thing first, before anything else
The hantavirus on the cruise ship is not the hantavirus in your attic. They are different strains.
The cruise ship outbreak is Andes virus, found in Argentina and Chile, and it's the only hantavirus that can spread person-to-person. That's why the WHO is tracing passengers across 17 countries.
The hantavirus that lives in U.S. mouse droppings is Sin Nombre virus, carried by the deer mouse. It does not spread person-to-person. You catch it one way only: by breathing in dust from rodent droppings, urine, or saliva. A neighbor with the flu cannot give it to you. A passenger off the cruise ship cannot give it to you. The mouse nest in your attic can.
Same name on the news, different disease at home. The cleanup steps below matter because of how Sin Nombre travels through dust, not because of anything happening on a boat.
What you're looking at, in order of severity
Not all droppings tell the same story.
A handful of dry, scattered pellets near the back of a closet. That is one or two visits, probably old, probably from a single mouse passing through. Low-volume contamination. Realistically, you can handle it with the right method.
A pile of droppings, a smell, or visible nesting material. That is a nest, or it was. The mouse may be gone, but its urine and saliva are still on the insulation. The contaminated area is bigger than what you can see, because mice mark territory by walking through their own waste and tracking it. Add a 3-foot radius to whatever you found and assume that whole area is hot.
Insulation visibly tunneled, gnaw marks on framing, or any contamination above your head. That is an active or recently active infestation. The dust above you means the air you're breathing has rodent particles in it every time you move. This is the situation that warrants a professional cleanup, not a DIY pass.
The deer mouse is the one you actually need to worry about. Smaller than a house mouse, white belly, two-tone tail, big black eyes. They live in basically every U.S. state and they carry Sin Nombre virus. House mice and rats can carry other rodent-borne diseases, but the hantavirus risk in the United States is a deer-mouse story.
If you cannot tell which species, assume deer mouse. Rural property, cabin, shed, attic with a roof vent. That is deer mouse territory.
The five mistakes that send people to the ER
Every one of these is in the CDC's published cleanup guidance. Every one of these is also what a normal homeowner does instead.
1. The vacuum. A standard vacuum is the single worst tool you own for this job. It picks up dust and blows it across the room through the exhaust. Even HEPA-rated home vacuums are tested to standards that don't cover viral particles in dried droppings. If you've already vacuumed an attic this week and you found droppings later, the air in that attic has been hot for hours.
2. The broom. Sweeping aerosolizes everything. Same problem as the vacuum, slightly more localized. Dry sweeping is the textbook wrong move and the CDC says so explicitly.
3. The mask. A surgical mask filters almost nothing relevant here. A KN95 helps for short exposures in small spaces. CDC and OSHA both call for an N100 or P100 respirator for any heavy infestation, and most homeowners don't own one. The N95s sitting in your COVID drawer are also probably fit-tested for nothing in particular and may not seal on your face today the way they did three years ago.
4. The "wet it down with bleach" assumption. The instruction is right. The assumption underneath it (that you found everything) is usually wrong. In a crawlspace, behind insulation, in a wall void, in a duct chase, you didn't see most of it. The droppings you spotted are the visible 10%.
5. The disposal step. CDC says double-bag the waste in heavy plastic, seal it, and put it directly in a covered outdoor trash can. Most people single-bag it and toss it in the kitchen bin, which puts the dust right back into the indoor air every time the can lid moves.
A real decision tree
Look at what you found and answer three questions in order.
Question 1: How big is the contaminated area?
If it's smaller than a bathroom (a single corner of a closet, the back of one cabinet, one shelf in the garage), you can probably handle it with the right method. Smaller than that means smaller than maybe 30 square feet of contiguous area.
If it's bigger than a bathroom (an attic, a crawlspace, a shed, a basement, an outbuilding, a cabin opened for the season), you are past the size where a careful homeowner cleanup is realistic. The CDC method assumes a contained, fully visible space. Attics and crawlspaces by definition aren't that.
Question 2: How dense is it?
A few scattered pellets in a clean space is one density. A nest, multiple piles, a smell, or visible tunneling through insulation is another. If you're at "nest or worse," skip to a pro. The disease load in nesting material is far higher than in stray droppings.
Question 3: Can you see all of it from one position?
If yes, you know what you're working with. If no, if the contamination disappears behind insulation, into wall voids, along ducts, or into eaves, what you see is a fraction of what's there. Crawlspaces and attic perimeters always fail this test.
If you answered "no" to any of those three, the right move is a biohazard cleanup crew, not a Saturday with a Swiffer.
If it really is small enough to handle yourself
This is the path most homeowners think they're on. Most aren't, but if you're confident you are, do it like this.
Open windows and ventilate the space for at least 30 minutes before you go in. Wear an N100 or P100 respirator (not an N95, not a surgical mask), nitrile gloves doubled, eye protection, and clothing you can wash separately on hot. Spray the droppings and the surrounding area with a 1:10 bleach-to-water solution or an EPA-registered disinfectant. Let it sit for at least five minutes. Wipe up wet, never dry. Double-bag everything in heavy plastic. Put it directly in an outdoor trash can with a lid. Wash your hands and arms with soap and warm water. Wash the clothes you wore on hot, by themselves.
If at any point during that you find more contamination than you expected, stop. The fact that you found more is the answer. Call a pro.
What we actually do on a hantavirus-risk job
A short list, because people ask.
We assess the entire space first, not just the visible part. We set up airflow that pushes contaminated air out of the structure, not into the living area. Full PPE: N100 or P100 respirators, body covering, doubled gloves, eye protection, never improvised. Wet cleanup only, with EPA-registered disinfectant, applied and dwelled for the full label time. Insulation that mice nested in gets removed and replaced, not cleaned. HEPA air scrubbing after wet cleanup, before reentry. Double-bagged biohazard disposal per state regulations. Then exclusion work, because the cleanup doesn't matter if the mice come back next month.
The whole protocol exists because aerosolized particles don't care about your weekend plans.
The 30-second version
If the contaminated area is bigger than a bathroom, call. If you see a nest, call. If you can't see all of it at once, call. If you've already vacuumed or swept, open every window in the building, leave, and call.
Don't sweep it. Don't vacuum it. Don't bleach-wipe it without ventilation and a real respirator. Open the windows, walk away, and let somebody who does this for a living finish the job.
That is what we are here for.
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Related reading
- [Hantavirus 2026: What the Cruise Ship Outbreak Means for Mouse Droppings in Your Attic](/blog/hantavirus-cruise-ship-home-risk). The news context and the deer-mouse / Sin Nombre virus explainer.