Most cases of HPS occur in rural areas. HPS was first identified in 1993. Most of the cases have been in Western and Plains states, but states as far east as New York, Pennsylvania, and Vermont have also reported at least one case. More recently, according to the CDC, cases of HPS stemming from related hantaviruses have been documented in Argentina, Brazil, Canada, Chile, Paraguay, and Uruguay.

The hantaviruses that cause HPS are carried by rodents. The deer mouse, the white-footed mouse, the cotton rat, and the rice rat are the most common carriers in the United States. House mice, roof rats, and Norway rats, which are found in urban areas in this country, do not carry hantaviruses that cause HPS. Voles and lemmings also carry hantaviruses, but not those that cause HPS. In Europe and Asia, Old World mice and rats carry other forms of hantaviruses that cause hemorrhagic fever with renal syndrome.

Mice and rats that are infected with the hantavirus leave the virus behind through their urine, droppings, and saliva. The virus is mainly transmitted to people when they breathe in air contaminated with the virus, the CDC says. This occurs when droppings or nesting materials are stirred up, sending the particles into the air. The virus also can be transmitted through breaks in the skin, by touching your nose or mouth after handling contaminated materials, through contaminated food or water, and—rarely—through mouse or rat bites. The types of hantavirus that cause HPS in the U.S. cannot be passed from one person to another, nor do they appear to infect animals such as dogs, cats, or farm animals.

Anything that puts you in contact with rodent droppings, urine, or nesting materials makes it more likely that you will be exposed to the hantavirus. Whether you touch the materials or stir them up and inadvertently inhale them, you are at risk for exposure. People who keep wild mice as pets are at risk. Hikers and backpackers are also at risk when they use shelters infested with rodents or camp in rodent habitats, the CDC says. Even when exposed to hantaviruses, however, the risk for infection by hantaviruses is low.

These are early symptoms, appearing one to five weeks after you become infected with the hantavirus. Other early symptoms include headaches, dizziness, chills, nausea, vomiting, diarrhea, and abdominal pain. Four to 10 days after these symptoms begin, late symptoms appear. These progress rapidly and include coughing and shortness of breath. At this point, the illness becomes life-threatening, as the lung fill with fluid. Prompt medical care is critical.

Because HPS is caused by a virus, antibiotics have no effect. There is no specific cure or treatment. Oxygen therapy helps the patient during severe respiratory distress, the CDC says. A person with HPS usually is placed in an intensive care unit and may need to use a mechanical respirator to breathe. The earlier the illness is recognized and the person brought to intensive care, the more effective treatment is likely to be.

If you live in an area where wild mice may get into your home, follow these CDC-suggested methods of prevention:

• Don't store food in open containers.
• Fix water leaks so the mice don't have a source of water.
• Keep windows and doors closed if you don't have tight-fitting screens.
• Use traps to catch mice that do enter your home.

Outdoors, follow these tips:

• Don't place birdfeeders near your home.
• Keep pet food in rodent-proof containers and don't leave uneaten pet food outside.
• Put trash and garbage in containers with tight-fitting lids.
• Keep grass cut short and bushes trimmed near the home.

You may find rodent droppings in places where you store food, particularly in cupboards and drawers. Droppings may also be inside closets or boxes. You may find rodent nests in cabinets, dressers, in or near boxes, behind and inside large appliances, and inside upholstered furniture, the CDC says. You may find boxes, containers, and plastic bags that have holes nibbled in them. Don't rely on spotting a mouse to know that you have a rodent problem. Rodents are active at night and try to stay away from people.