CDC answers your questions about
HANTAVIRUS
Public Information Area
Part Three:
How Do I Prevent HPS?

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How Do I Prevent HPS?

Eliminate or minimize contact with rodents

Make your home, workplace, vacation home or campsite unattractive to them!

Why is this so important? If rodents don't find that where you are is a good place for them to be, too—that means lots of easy-to-get-food and nesting material—then you're less likely to come into contact with them. And recent research results show that many people who have beome ill with HPS got the disease after having been in frequent contact with rodents and/or their droppings around a home or a workplace. In addition, many people who become ill reported that they had not seen rodents or their droppings at all. Therefore, if you live in an area where the carrier rodents like the deer mouse are known to live, it makes sense to try to keep your home, vacation place, workplace—and as far possible, campsite—clean.

So, that said, what can you do?

Tips For Preventing HPS:  Prevention Indoors and Outdoors

Indoors:

• Keep a clean home, especially kitchen (wash dishes, clean counters and floor, keep food covered in rodent-proof containers).
  
• Keep tight-fitting lid on garbage, discard uneaten pet food at the end of the day.
  
• Set and keep spring-loaded rodent traps. Set traps near baseboards because rodents tend to run along walls and in tight spaces rather than out in the open.
  
• Set EPA-approved rodenticide with bait under plywood or plastic shelter along baseboards. These are sometimes known as "covered bait stations." Remember to follow product use instructions carefully, since rodenticides are poisonous to pets and people, too.
  
• If bubonic plague is a problem in your area, spray flea killer or spread flea powder in the area before setting traps. This is important. If you control rodents but do not control fleas as well, you may increase the risk of infection with bubonic plague, since fleas will leave rodents once the rodents die and will seek out other food sources, including humans.
  
• Seal all entry holes 1/4 inch wide or wider with steel wool, cement, wire screening or other patching materials, inside and out.

Outdoors:

• Clear brush, grass and junk from around house foundations to eliminate a source of nesting materials.
  
• Use metal flashing around the base of wooden, earthen or adobe homes to provide a strong metal barrier. Install so that the flashing reaches 12 inches above the ground and six inches down into the ground.
  
• Elevate hay, woodpiles and garbage cans to eliminate possible nesting sites. If possible, locate them 100 feet or more from your house.
  
• Trap rodents outside, too. Poisons or rodenticides may be used as well, but be sure to keep them out of the reach of children or pets.
  
• Encourage natural predators such as non-poisonous snakes, owls and hawks.
  
• Remember, totally getting rid of all rodents isn't feasible, but with ongoing effort you can keep the population very low.

Tips For Preventing HPS:   Clean up infested areas, using safety precautions:

• Put on latex rubber gloves before cleaning up.
  
• Don't stir up dust by sweeping up or vacuuming up droppings, urine or nesting materials.
  
• Instead, thoroughly wet contaminated areas with detergent or liquid to deactivate the virus. Most general purpose disinfectants and household detergents are effective. However, a hypochlorite solution prepared by mixing 1 and 1/2 cups of household bleach in 1 gallon of water may be used in place of commercial disinfectant. When using the chlorine solution, avoid spilling the mixture on clothing or other items that may be damaged.
  
• Once everything is wet, take up contaminated materials with a damp towel, then mop or sponge the area with disinfectant.
  
• Spray dead rodents with disinfectant, then double-bag along with all cleaning materials and bury or burn—or throw out in appropriate waste disposal system. If burning or burying isn't feasible, contact your local or state health department about other disposal methods.
  
• Finally, disinfect gloves before taking them off with disinfectant or soap and water. After taking off the clean gloves, thoroughly wash hands with soap and warm water.

When going into cabins or outbuildings (or work areas) that have been closed for awhile, open them up and air out before cleaning.

Strength and Quantity of Hyperchlorite Solutions: How Much Is Enough?

Strength of Hyperchlorite Solution

Special Pathogens Branch recommends a 10% bleach solution be used to inactivate hantaviruses.   A 10% solution corresponds to 1 and a half cups of household bleach per gallon of water, or 1 part bleach to ten parts water.

Why a 10% solution?  Household bleach is made of 5.25% Sodium Hypochlorite (52,500 ppm); therefore, a 1% bleach bleach solution is 525 ppm. Some experiments have shown that 200 ppm (or even less in some experiments) will inactivate most viruses. Therefore it would seem that a 1% solution of household bleach might be adequate. However, hypochlorite is substantially and quickly inactivated in the presence of organic matter. So, although 1% may be adequate for surface decontamination, a 10% dilution may be a better choice for inactivation of virus when one is cleaning out areas which have been infested by rodents. This 10% concentration is currently supported in CDC Infection Control recommendations.

Amount of Hyperchlorite Solution

No matter what concentration of solution is used, only the outside layer of the material to be disinfected is bound with the chlorine molecules in the bleach solution, unless the object is entirely soaked through. Complete soaking is more easily achieved when greater quantities of water are used. Therefore, it is recommended that the material being sprayed or poured over be thoroughly drenched, in order to maximize penetration of the material.

References with Regard to Hyperchlorite Solutions

Garner JS, Favero MS. Guidelines for handwashing and hospital environmental control, 1985. MMWR, 1987;36(25 Supplement). MMWR 1988;37(24). Available online at CDC.

Favero MS, Bond WW. Sterilization, disinfection, and antisepsis in the hospital. 1991. In: Manual of Clinical Microbiology, American Society for Microbiology. Washington, D.C. Chapter 24: 183-200.

What if my house or workplace is heavily infested with rodents?

You should get help from a professional exterminator if you see lots of droppings or rodents—you may have a bad infestation problem. Or you can contact your local health authorities for advice.

CDC has recommendations for how heavy infestations may most safely be handled. See below!

What if I work around rodents frequently? What should I do?

You may wish to read the CDC recommendations for "Workers in Affected Areas Who Are Regularly Exposed to Rodents".  See below!

Why all the fuss about spraying disinfectant, washing traps with bleach, and such?

These viruses are surrounded by a lipid (fatty) envelope, so they are somewhat fragile. The lipid envelope can be destroyed and the virus killed by fat solvents like alcohol, ordinary disinfectants and household bleach. That is why one of the most important ways to prevent transmitting the disease is to carefully wet down dead rodents and areas where rodents have been with disinfectant and/or bleach. When you do this, you are killing the virus itself and reducing the chance that the virus will get into the air.

Summing up:  How to prevent HPS

• make your home, workplace, vacation home unattractive to them
• clean up infested areas using safety precautions
• wet down infested areas with bleach/disinfectant to kill the virus before it aerosolizes
• in other words: AIR OUT, SEAL UP, TRAP UP, CLEAN UP

Special Precautions for Homes of Persons with Confirmed Hantavirus Infection or Buildings with Heavy Rodent Infestations

Special precautions should be used for cleaning homes or buildings with heavy rodent infestations in areas where HPS has been reported. If you are attempting to deal with such an infestation, it is recommended that you contact the responsible local, state, or federal public health agency for guidance.

The special precautions may also apply to vacant dwellings that have attracted numbers of rodents while unoccupied and to dwellings and other structures that have been occupied by persons with confirmed hantavirus infection.

Workers who are either hired specifically to perform the clean-up or asked to do so as part of their work activities should receive a thorough orientation from the responsible health agency about hantavirus transmission and should be trained to perform the required activities safely.

Precautions To Be Used:

• A baseline serum sample, preferably drawn at the time these prevention activities are initiated, should be available for all persons conducting the clean-up of homes or buildings with heavy rodent infestation. The serum sample should be stored at -20 C.
• Persons involved in the clean-up should wear coveralls (disposable if possible), rubber boots or disposable shoe covers, rubber or plastic gloves, protective goggles, and an appropriate respiratory protection device, such as a half-mask air-purifying (or negative-pressure) respirator with a high-efficiency particulate air (HEPA) filter or a powered air-purifying respirator (PAPR) with HEPA filters. 

  Please note:  the HEPA classification recently has been discontinued.  Please read "Update On the Nomenclature and Use of Respirators as a Precaution for Hantavirus Infection, February, 1999" for details.  See below!

• Personal protective gear should be decontaminated upon removal at the end of the day. If the coveralls are not disposable, they should be laundered on site. If no laundry facilities are available, the coveralls should be immersed in liquid disinfectant until they can be washed.
• All potentially infective waste material (including respirator filters) from clean-up operations that cannot be burned or deep buried on site should be double bagged in appropriate plastic bags. The bagged material should then be labeled as infectious (if it is to be transported) and disposed of in accordance with local requirements for infectious waste.
• Workers who develop symptoms suggestive of HPS within 45 days of the last potential exposure should immediately seek medical attention. The physician should contact local health authorities promptly if hantavirus-associated illness is suspected. A blood sample should be obtained and forwarded with the baseline serum through the state health department to CDC for hantavirus antibody testing.

Precautions for Workers in Affected Areas Who are Regularly Exposed to Rodents

Persons who frequently handle or are exposed to rodents (e.g., mammalogists, pest-control workers) in the affected area are probably at higher risk for hantavirus infection than the general public because of their frequency of exposure. Therefore, enhanced precautions are warranted to protect them against hantavirus infection.

Precautions To Be Used:

• A baseline serum sample, preferably drawn at the time of employment, should be available for all persons whose occupations involve frequent rodent contact. The serum sample should be stored at -20°C.
• Workers in potentially high-risk settings should be informed about the symptoms of the disease and be given detailed guidance on prevention measures.
• Workers who develop a febrile or respiratory illness within 45 days of the last potential exposure should immediately seek medical attention and inform the attending physician of the potential occupational risk of hantavirus infection. The physician should contact local health authorities promptly if hantavirus-associated illness is suspected. A blood sample should be obtained and forwarded with the baseline serum through the state health department to CDC for hantavirus antibody testing.
• Workers should wear a half-face air-purifying (or negative-pressure) respirator or PAPR equipped with HEPA filters when removing rodents from traps or handling rodents in the affected area.  (Please note:  the HEPA classification recently has been discontinued.  Under the new classification system, the N-100 filter type is recommended.  Read the Federal Occupational Safety and Health Administration (OSHA) directive online, at "OSHA Directives: CPL 2-0.120 - Inspection procedures for the Respiratory Protection Standard".)
• Respirators (including positive-pressure types) are not considered protective if facial hair interferes with the face seal, since proper fit cannot be assured. Respirator use practices should be in accord with a comprehensive user program and should be supervised by a knowledgeable person.
• Workers should wear rubber or plastic gloves when handling rodents or handling traps containing rodents. Gloves should be washed and disinfected before removing them, as described above.
• Traps contaminated by rodent urine or feces or in which a rodent was captured should be disinfected with a commercial disinfectant or bleach solution. Dispose of dead rodents as described in the section on Eliminating Rodents inside the Home.
• Persons removing organs or obtaining blood from rodents in affected areas should contact the Special Pathogens Branch, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, [telephone (404) 639-1115] for detailed safety precautions.

Precautions for Other Occupational Groups Who Have Potential Rodent Contact

Insufficient information is available at this time to allow general recommendations regarding risks or precautions for persons in the affected areas who work in occupations with unpredictable or incidental contact with rodents or their habitations. Examples of such occupations include telephone installers, maintenance workers, plumbers, electricians, and certain construction workers. Workers in these jobs may have to enter various buildings, crawl spaces, or other sites that may be rodent infested. Recommendations for such circumstances must be made on a case-by-case basis after the specific working environment has been assessed and state or local health departments have been consulted.

Update On the Nomenclature and Use of Respirators as a Precaution for Hantavirus Infection
February, 1999

The CDC Interim Recommendations for Risk Reduction for Hantavirus Infection(1)  describe precautions for persons who are involved in the cleanup of homes of confirmed cases of hantavirus infection or of areas with heavy rodent infestation and for workers in affected areas who are regularly exposed to rodents. Among these precautions is the wearing of one of the following types of respirators(2) equipped with a high-efficiency particulate air (HEPA) filter:

Recent changes in the nomenclature and certification of the type of filters used in these respirators include the discontinuation of the HEPA designation and the designation of new classes of filters.  As shown on the chart below, the N-100 (99.97) is equivalent to the previous HEPA filter.

Use of an N-100 filter should provide the same protection as the HEPA filter. Due to the nature of the virus, no studies have been able to test the efficacy of either the HEPA or N-100 filters in protecting against HPS transmission. Available evidence suggests that HPS is transmitted by inspiring small (less than 5 micron) viral particles in aerosols which the N-100 is the most effective in removing.

Cautions: As described in CDC Interim Recommendations for Risk Reduction for Hantavirus Infection, all negative-pressure respirators are fit-dependent. Anything that interferes with the respirator’s face seal, such as facial hair, will allow ambient air to bypass the filter medium in the respirator(3). Ideally, users should be fit-tested with the same make, model, style, and size of respirator that will be actually used. Respirator practices should follow a comprehensive user program and be supervised by a knowledgeable person.

New Classes of Filters for Respiratory Protection Devices(4)

†† number indicates % efficiency in removing monodispersed particles 0.3 micrometers in diameter.

Authority for testing and certifying these respirators has been given exclusively to NIOSH. For additional information:

• contact the Industrial Hygiene Section, Office of Health & Safety, CDC at 404 639-3112.
• Read the NIOSH directive online, at "OSHA Directives: CPL 2-0.120 - Inspection procedures for the Respiratory Protection Standard".

(1) MMWR Recommendations and Reports, July 30, 1993; 42 [RR-11]: 1-13)

(2) All of these respirators can be purchased from commercial suppliers of laboratory safety equipment.  The items displayed here are intended to show the general design of the respirator and do not constitute endorsement of any particular brand of respirator.

(3) MMWR 47(40): 1045-1049, demonstrates importance of fit testing for all negative-pressure respirators.

(4) As described in NIOSH 42, CFR 84.

Precautions for Campers and Hikers in the Affected Areas

There is no evidence to suggest that travel into areas where HPS has been reported should be restricted. Most usual tourist activities pose little or no risk that travelers will be exposed to rodents or their urine and/or droppings.

However, persons who do outdoor activities such as camping or hiking in areas where the disease has been reported should take precautions to reduce the likelihood of their exposure to potentially infectious materials.

Useful Precautions:

• Avoid coming into contact with rodents and rodent burrows or disturbing dens (such as pack rat nests).
• Air air, then disinfect cains or shelters before using them. These places often shelter rodents.
• Do not pitch tents or place sleeping bags in areas in proximity to rodent droppings or burrows or near areas that may shelter rodents or provide food for them (e.g., garbage dumps or woodpiles).
• If possible, do not sleep on the bare ground. In shelters, use a cot with the sleeping surface at least 12 inches above the ground. Use tents with floors or a ground cloth if sleeping in the open air.
• Keep food in rodent-proof containers!
• Promptly bury (or--preferably--burn followed by burying, when in accordance with local requirements) all garbage and trash, or discard in covered trash containers.
• Use only bottled water or water that has been disinfected by filtration, boiling, chlorination, or iodination for drinking, cooking, washing dishes, and brushing teeth.
• And last but not least, do not play with or handle any rodents that show up at the camping or hiking site, even if they appear friendly.

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1999, Special Pathogens Branch
Division of Viral and Rickettsial Diseases
National Center for Infectious Diseases
The Centers for Disease Control and Prevention (CDC)
U.S. Department of Health and Human Services