• U.S. Department of Labor
  • Occupational Safety and Health Administration
  • Directorate of Enforcement Programs
  • Office of Health Enforcement

Workplace Precautions Against West Nile Virus

Safety and Health Information Bulletin

SHIB 08-29-2003 (B);
update 08/12

This Safety and Health Information Bulletin is not a standard or regulation, and it creates no new legal obligations. The Bulletin is advisory in nature, informational in content, and is intended to assist employers in providing a safe and healthful workplace. Pursuant to the Occupational Safety and Health Act, employers must comply with hazard-specific safety and health standards and regulations promulgated by OSHA or by a state with an OSHA-approved state plan. In addition, pursuant to Section 5(a)(1), the General Duty Clause of the Act, employers must provide their employees with a workplace free from recognized hazards likely to cause death or serious physical harm.


OSHA has developed this safety and health bulletin on Workplace Precautions against West Nile Virus to provide relevant information regarding this illness to employers, workers, and other interested parties.


West Nile Virus (WNV) infection is a potentially serious illness transmitted to humans primarily by mosquitoes. WNV is known to infect birds and other animals as well as humans. While it is not known exactly how long this virus has been in the United States, the Centers for Disease Control and Prevention (CDC) has documented over 30,000 human cases of the infection in the U.S. since 1999. It is considered a seasonal epidemic that flares up in the summer and continues into the fall. Up-to-date information on the number of cases and fatalities due to WNV infection can be obtained on the CDC's WNV web page.

CDC reports that in four out of five cases, persons infected with WNV show no symptoms.  In almost 20% of the cases, infections result in very mild flu-like symptoms, called West Nile fever. These mild cases of West Nile fever normally last only a few days and are not believed to cause any long-term effects. According to the CDC, severe cases occur in one out of 150 people infected with WNV and result in "West Nile encephalitis," an inflammation of the brain, "West Nile meningitis," inflammation of the membrane around the brain, or "West Nile meningoencephalitis," an inflammation of the brain and the membrane around it. The signs and symptoms of severe disease may last several weeks and may have permanent neurological effects.

The typical time from infection to the onset of signs and symptoms is 3 to 14 days. Signs and symptoms of the milder West Nile Fever illness can last a few days to several weeks and include:

  • Headache
  • Fever
  • Tiredness
  • Body aches
  • Nausea and vomiting
  • Sometimes, swollen lymph nodes
  • Sometimes, a skin rash on the body

The CDC reports that with more severe infection (West Nile encephalitis or meningitis), the signs and symptoms lasts several weeks, sometimes resulting in permanent neurological problems, and include:

  • Headache
  • High fever
  • Stiffness in the neck
  • Nausea and vomiting
  • Stupor or Disorientation (in very severe cases, coma)
  • Tremors and convulsions
  • Muscle weakness (in very severe cases, paralysis)
  • Loss of vision

There is no specific treatment for WNV infection. In mild cases the symptoms resolve on their own. In more severe cases, people usually need to go to the hospital where they can receive supportive treatment including intravenous fluids, help with breathing and nursing care. Pregnant women and nursing mothers should discuss with their doctor if there are concerns or if they develop symptoms that could be WNV.

Although the infection has been documented in laboratory workers working with the virus itself, most documented human cases in the U.S. have resulted from mosquito bites. The risk of getting infected with WNV can often be reduced or eliminated with use of preventive measures that minimize or eliminate mosquito bites. To lessen the chances of mosquito bites:

  • Reduce or eliminate mosquito populations by disrupting mosquito breeding grounds (i.e., get rid of sources of stagnant or standing water weekly; mosquitoes can breed in any stagnant puddle that lasts more than 4 days).
  • Cover as much of the skin as possible by wearing shirts with long sleeves, long pants and socks whenever possible.
  • Use insect repellent containing an EPA-registered active ingredient.
  • When possible, consider staying indoors before dawn and after dusk; many mosquitoes are most active during these hours.
  • Have functional screens on your workplace's windows and doors to keep mosquitoes out.

These and other methods of reducing risk of WNV-infection are discussed in the sections that follow.

What occupations are at risk?

In general, WNV is transmitted to humans via mosquito bites, therefore workers primarily working outside are at risk, particularly in warmer weather (when mosquitoes are more likely to be present). In regions of the U.S. with warm climates, workers are at risk for a longer period. At risk occupations include farm workers, loggers, landscapers/groundskeepers, construction workers, painters, summer camp workers, pavers, and other outdoor workers.

In at least two cases, laboratory workers handling WNV-infected fluids or tissues have become infected; therefore, these workers should also take precautions against WNV infection. An exposure may occur due to a needlestick, an accidental cut, or an existing open wound that comes in contact with infectious fluid or tissues. Laboratory workers who work with WNV- infected animals or who handle other tissue, fluid or other WNV-infected material should report to their supervisors if they believe they may have had an exposure that could result in infection. Laboratory workers handling human blood or other potentially infectious material require protection as described in OSHA's Bloodborne Pathogens Standard, 29 CFR 1910.1030.

As of August 28, 2012, OSHA is not aware of any documented cases of healthcare workers who have become infected following treatment of patients with WNV infection. Nevertheless, healthcare workers and emergency response personnel must continue to use universal precautions to protect against exposure to human blood and other potentially infectious materials (OPIM) as required by OSHA's Bloodborne Pathogens Standard, 29 CFR 1910.1030.

How can employers protect workers?

As with all workplace hazards, employers should use the following hierarchy of control- measures to minimize or eliminate WNV infections among their workers:

Engineering/Administrative Controls

Employers with outdoor workers:

  • Be aware of outside working conditions, i.e., the presence of equipment or areas where water may accumulate.
  • Inspect work areas and, where possible, get rid of sources of stagnant or standing water to remove a potential breeding ground of mosquitoes.
  • Encourage workers to take extra precautions whenever mosquitoes are present and biting (for example, mosquito swarms are often present at dusk or at dawn).
  • Workers should avoid touching dead birds. Instead, have them report dead birds and forward the report to local authorities. The local authorities may tell you how to dispose of the bird properly after they log your report. (CDC has links to state and local government sites on their web page).

Healthcare/Laboratory employers:

  • Use of standard precautions is recommended.
  • If workers are exposed to blood and/or other potentially infectious materials, OSHA's bloodborne pathogens standard, 29 CFR 1910.1030, must be followed, including establishing and implementing a workplace Exposure Control Plan and the providing sharps with engineered sharps injury protection (SESIP) to avoid sharps-related injuries.
  • Monitor and record incidents as well as actual injuries in laboratories involving possible exposure to WNV. Encourage workers to report injuries and illnesses that occur in laboratories where WNV-infected tissues or fluid is present. Keep track of workers who report symptoms that are consistent with WNV infection in labs where WNV is present.

Worker Training

Employers should provide training to workers who may be at risk. Training should cover the potential hazards and the risks of WNV exposure and infection. Knowing key steps that workers themselves can take to minimize the risk of getting bitten by mosquitoes can help to reduce the risk of WNV infection. Workers who work outdoors in warm climates should be made aware of the appropriate personal protective equipment and work practices that protect against mosquito bites. Workers should also be made aware that mosquitoes are more likely to swarm during late evening and early morning hours and extra precautions should be followed at these times. Workers should also be encouraged to report dead birds and should be instructed not to pick up dead birds with bare hands.

Personal Protection

Employers with outdoor workers:

In warm weather, encourage workers who work outdoors to wear light-weight, loose clothing. This type of clothing protects workers against the sun's harmful rays, and also provides a barrier to mosquitoes. Employers may also want to have insect repellents available for workers to protect against mosquitoes.

Healthcare/Laboratory employers:

In laboratories and healthcare settings employers must provide gloves. As some workers may have allergies to latex gloves, employers should also make available non-latex gloves as an alternative. In workplaces where animal studies are performed on WNV-infected animals, employers must provide gloves that will prevent cutting injuries (e.g. stainless steel mesh gloves). Under 29 CFR 1910.132 , employers must evaluate the work environment and, where there is a potential for skin or mucous membrane contact with blood and or other tissues, also provide additional personal protective equipment (PPE) to affected workers (e.g., safety glasses, and/or face shields, where appropriate, and gowns). OSHA's bloodborne pathogen standard has provisions requiring the use of PPE when working with human blood.

How can employers reduce or eliminate mosquito breeding grounds?

Employers should keep in mind that eliminating mosquito breeding grounds is a highly effective way of reducing mosquito populations and the number of mosquito bites. Mosquitoes lay eggs in standing water. Take the following steps to eliminate standing water in the workplace:

  • Avoid leaving containers that can accumulate water in an uncovered or upright position, such as, wheelbarrows, drums, buckets, cans, tarps and other containers.
  • Drain or pump out collected water from newly constructed swimming pools, rain gutters and ditches.
  • Properly store any open containers in the work area that are not being used such as buckets and cans.
  • Create holes to drain water from containers that cannot be thrown out.
  • Fill in any potholes, patches and other areas where water is likely to accumulate.
  • Frequently check ponds, birdbaths, animal feeding and drinking troughs and other bodies of standing water. Use aeration, wherever possible, as a way to prevent mosquito growth.
  • Change water in animal feeders every few days.

How can workers working outdoors protect themselves?

It may not always be possible to eliminate all potential mosquito breeding grounds. For example, workers in logging operations may not be able to determine all areas of water accumulation in their work environment. Knowledge of some key steps that workers can take to minimize the risk of mosquito bites is, therefore, important in reducing the risk of WNV infection. Workers who work outdoors should be aware that the use of personal protective equipment and techniques is essential to preventing mosquito bites. Especially when working at sites where mosquitoes may be active and biting, workers should use the following steps to minimize the likelihood of getting bitten:

  • Cover as much of your skin as possible by wearing shirts with long-sleeves, long pants, and socks whenever possible (use light weight clothing to minimize the potential for heat-induced illnesses).
  • Avoid use of perfumes and colognes when working outdoors during peak times when mosquitoes may be active; mosquitoes may be more attracted to individuals wearing perfumes and colognes.
  • Use insect repellent containing an EPA-registered active ingredient. All of the EPA-registered active ingredients have demonstrated repellency however some provide more longlasting protection than others. Research suggests that repellents containing DEET (N,N-diethyl-m-toluamide) or picaridin (KBR 3023) typically provide longer-lasting protection than the other products, and oil of lemon eucalyptus (p-menthane-3,8-diol) provides longer lasting protection than other plant-based repellents. Permethrin is another long-lasting repellent that is intended for application to clothing and gear, but not directly to skin.
  • Choose a repellent that provides protection for the amount of time that you will be outdoors. In general, the more active ingredient (higher concentration) a repellent contains, the longer it will protect against mosquito bites. For example, the more DEET a repellent contains, the longer time it can protect you from mosquito bites, with protection times ranging from 1 hour (4.75% DEET) to 5 hours (23.8% DEET).  However, products with greater than 50% DEET were not shown to offer additional protection and protection times can vary due to temperature, perspiration, and water exposure.
  • To avoid reaction to DEET or other ingredients of insect repellents, read and follow the directions on all insect repellent before use. Spray insect repellent on the outside of your clothing, as it is possible for mosquitoes to bite through thin clothing.
  • Do NOT spray insect repellent on skin that is under clothing.
  • Do NOT apply insect repellent to skin that is already irritated, or to cuts/lacerations.
  • Do NOT spray aerosol or pump products in enclosed areas. Do NOT spray a pump or aerosol product directly on your face. First spray on hands and carefully rub on face (do not allow insect repellent to contact your eyes and mouth).
  • After returning indoors, use soap and water to wash skin that has been treated with insect repellent.
  • Workers should protect themselves from skin contact with dead birds. CDC recommends using gloves or an inverted plastic bag when handling dead birds.

Note: Additional resources are provided below for information on the safe use of insect repellent.

The U.S. Environmental Protection Agency (EPA) provides information on how to safely use insect repellents. Information is located on-line in the U.S. EPA: How to Use Insect Repellents Safely page.

Additional information on the safe use of insect repellents can be obtained from a question and answer document posted on the Centers for Disease Control's (CDC) Website. The document is titled FAQ: Insect Repellent Use & Safety.

The National Pesticide Information Center (NPIC) provides useful contact information for persons with further questions on the use of insect repellents for mosquito control.

What can healthcare/laboratory workers do to protect themselves?

Healthcare workers, emergency personnel and laboratory workers who may be in contact with human blood or OPIM must follow OSHA's Bloodborne Pathogens Standard (29 CFR 1910.1030). These workers who are not exposed to human blood or OPIM, but may be exposed to WNV should follow the recommendations below:

  • Follow workplace standard operating procedures (in other words, workplace exposure control plans) and use the engineering controls and work practices available in the workplace to prevent exposure to blood or other potentially infectious materials.
  • Do NOT bend, recap, or remove contaminated needles or other contaminated sharps.
  • Use sharps with engineered sharps injury protection (SESIP) to avoid sharps-related injuries.
  • Minimize the aerosolization of blood or body fluids as much as possible.
  • Always wash hands after removing gloves and prior to leaving the workplace.
  • Use personal protective equipment (i.e., gloves, gowns, safety glasses, and/or face shields, where appropriate).
  • Report all needlesticks, lacerations, and other exposure incidents as soon as possible to supervisors.

Where can I get additional information on West Nile Virus?

OSHA has a Fact Sheet and a Quick Card.

Several public health agencies have published information on the prevention of WNV infection. Information published by the Centers for Disease Control and Prevention can be obtained at the CDC WNV Home Page.

Contacts for state and local health departments are listed.

The National Institute for Occupational Safety and Health offers information for employers and workers at West Nile Virus.