Two cases of hantavirus reported in King County since December, 2016: Be aware of health risks associated with deer mouse infestations

Hantavirus can cause a rare but deadly disease called Hantavirus Pulmonary Syndrome (HPS). In Washington State hantavirus is carried primarily by deer mice. Over the last several months, two people in King County have become ill with HPS, and one person died.

A person gets HPS by breathing in hantavirus. This can happen when dust from dried rodent urine, saliva, and droppings that contain hantavirus are stirred up in the air. People can also get infected by touching rodent urine, droppings, or nesting materials that contain the virus, and then touching their eyes, nose, or mouth. It’s also possible to get HPS from a rodent bite. The disease does not spread person-to-person.

Deer mouse: Determined to be one of the reservoirs and transmitters of the hantavirus.

The person who died was a man in his 30s who lived in Issaquah. He went to the emergency room on February 23rd, and died on February 24th. Tests that Public Health received on March 1st revealed he had hantavirus. The other person who was diagnosed with hantavirus lives in Redmond. She is a woman in her 50s and was diagnosed in December, 2016. She has recovered.

Hantavirus is a rare disease in Washington State. The last known case of hantavirus acquired locally in King County was in 2003. The 2003 case and the two cases reported here today are the only known instances of hantavirus infection acquired in King County. There have also been 3 other cases reported to Public Health since 1997 where the people were thought to have been infected outside of the county.

“While it’s a concern that there are two locally-acquired cases relatively closely together, at this point, we do not know whether this indicates a general increase in risk for our area,” said Dr. Jeff Duchin, Health Officer for Public Health – Seattle & King County. “Either way, these cases serve as an important reminder to be aware of the risk of hantavirus, know the symptoms of hantavirus, and how to clean up rodent infestations.”

What animals carry hantavirus?

Hantavirus is carried by deer mice in our state.  In other parts of the U.S., other rodents can also carry the disease. It is not carried by rats in our region.

Who is at risk for hantavirus infection?

Any activity that puts people in contact with rodent droppings, urine, saliva, or nesting materials can place you at risk for infection. Hantavirus is spread when virus-containing particles from rodent urine, droppings, or saliva are stirred into the air. It is important to avoid actions that raise dust, such as sweeping or vacuuming. Infection occurs when virus particles are breathed in.

Rodent infestation in and around the home (including infested sheds, outbuildings, cabins and barns) is the primary risk for hantavirus exposure. Cases of hantavirus associated with rodent-infested automobiles have also been reported. Deer mice live in wooded areas in Washington state and can nest in nearby homes, sheds, cabins, other structures, and cars. A home or building does not need to be old or dilapidated to have a problem with rodents.

Potential risk activities for HPS include:

  • Opening or cleaning previously unused buildings, cabins, sheds, barns, garages and storage facilities (including those which have been closed during the winter) is a potential risk for hantavirus infections, especially in rural settings.
  • Housecleaning activities in and around homes with rodent infestations (see information on safe cleaning in our Hantavirus Fact Sheet).
  • Work-related exposure: Construction, utility and pest control workers can be exposed when they work in crawl spaces, under houses, or in vacant buildings that may have a rodent population.
  • Campers and hikers: Campers and hikers can be exposed when they use infested trail shelters or camp in other rodent habitats.
  • Exposure to cars, trailers, or mobile homes where rodents are living (see specific guidance for cleaning up vehicles).

The chance of being exposed to hantavirus is greatest when people work, play, or live in closed spaces where rodents are actively living. Many people who have contracted HPS reported that they had not seen rodents or their droppings before becoming ill. Therefore, if you live in an area where the deer mice are known to live, take precautions to prevent rodent infestations even if you do not see rodents or their droppings.

Symptoms of hantavirus:

If you have been exposed to rodents or rodent infested buildings and have symptoms, see your doctor immediately and tell them about your possible rodent exposure. Symptoms begin 1-8 weeks after inhaling the virus. It typically starts with 3-5 days of illness that is similar to the flu, including fever, sore muscles, headaches, nausea, vomiting, and fatigue.  As the disease gets worse, it causes coughing and shortness of breath. People with hantavirus are usually hospitalized, and about one out of three people diagnosed with HPS have died.

Preventing hantavirus

Keep wild rodents out of your home and workplace by removing their sources of food, water, and shelter. If you do have a rodent infestation, it’s important to take precautions to safely clean up the area. Learn specifically how to prevent rodent infestation and clean up rodent infestations at Public Health’s hantavirus factsheet and the CDC website

Heavy rodent infestations

Public Health should be consulted (at 206-263-9566) and special precautions are suggested for cleaning homes or buildings with:

  • heavy rodent infestations (piles of feces, numerous nests or dead rodents)
  • vacant dwellings that have attracted rodents while unoccupied
  • dwellings and other structures that have been occupied by persons with confirmed hantavirus infection.

Public Health recommends hiring professional pest control services in these situations.

Rodent infestations in cars

There have been reports of rodent infestations in vehicles as a possible means of hantavirus exposure. The same principles that are described for cleaning a home infested with rodents would apply to cleaning a vehicle infested with rodents. Signs of rodents include a foul odor, chewed wires or other components under the hood, and visible nesting material and excrement in the vehicle. (See guidance on cleaning up after rodents in cars).

More information

For more information and specific instructions to avoid rodents and clean up after an infestation, visit Public Health’s Hantavirus Pulmonary Syndrome website.

The Centers for Disease Control and Prevention (CDC) hantavirus web site  is a good source of information on hantavirus risk, transmission, symptoms and prevention measures.

Information from the Washington State Department of Health on hantavirus is available at

In addition, read the Public Health Insider for our 2015 article about the search for hantavirus.

Originally posted on March 21, 2017.guidance for cleaning up vehiclesguidance on cleaning up after rodents in cars

7 thoughts on “Two cases of hantavirus reported in King County since December, 2016: Be aware of health risks associated with deer mouse infestations

  1. How about include what part of Issaquah this person lived in so we have a better idea of where the danger is.

    1. Hi John,

      Thanks for reaching out.

      Prevention measures for hantavirus are the same regardless of where you may live. But, deer mice tend to live in more rural/semi-rural areas, so some parts of King County may have higher populations of deer mice than others. In urban areas, the house mouse is more likely to cause an infestation. Deer mice tend to not cause infestations in homes as frequently as house mice.

      Therefore, if you live in an area where the deer mice are known to live, take precautions to prevent rodent infestations even if you do not see rodents or their droppings. For more information on rodent prevention and clean up please visit our rat prevention page: and hantavirus factsheet:

    2. 100% of Issaquah has deer mice …. really. Even downtown Issaquah has deer mice. In fact if you live in Sammamish, Woodinville, Renton, most of New Castle, and the eastern sections of Bellevue and Redmond your home is likely to have deer mice in the crawlspace or attic.

      Despite this, and that it is suspect that a high percentage (up to 40%) of deer mice in Washington state carry the Hanta Virus, it does require unique situations for someone to contract the Hanta virus and succumb to it.

  2. I have found deer mice at my garage on Vashon Island. I have trapped several of them over the past months. They seem to come into the garage after the main door has been open for some time, although there may be an infestation within the garage itself. However, no indication of virus or disease exposure.

  3. I have been house hunting in Burien, Tukwila, Des Moines, Kent and Federal Way. But I don’t know if any of these locations have been infested with rats or deer rats. I have been sick. Since this is air born and can be inhaled, is there anything obvious to look for?

    1. Hi Laura,
      In general, you’d have to have considerable exposure to deer mouse droppings or urine and be involved in activity that would stir up dust from dried mouse urine or droppings, like sweeping or moving boxes in a rodent infested area. If you are just entering homes during your house hunting, you’d be unlikely to have that level of exposure.

      If you are concerned about your illness, the period of time from an exposure to hantavirus and developing symptoms is anywhere from one to eight weeks. The earliest symptoms are similar to influenza (“flu”), but if you have been around deer mice and develop symptoms of fever, muscle aches, fatigue, or shortness of breath, see your health care provider and them him/her that you have been around rodents.

  4. I am new to the area and did not know until recently this was an issue. Last week I took my toddler to play in our backyard. I believe that we had an issue and have rodent runways all through the yard. I’m concerned about the exposure to myself and son as we were playing soccer and he laid on the ground at one point. I now know the runways are probably come or deer mice. How can I rule out deer mice?

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