CDC Interim Guidance for Workers who are Employed at Commercial Swine Farms: Preventing the Spread of Influenza A Viruses
This guidance is issued with the goal of preventing the spread of influenza viruses from people to pigs and from pigs to people. These recommendations are for people who work with pigs in the commercial production (farm) setting. The following interim recommendations are based on what are deemed optimal precautions for protecting workers exposed to pigs with known or suspected influenza on production premises AND for protecting pigs from people with influenza.
Influenza A viruses that circulate in pigs are different from the influenza viruses circulating in people. Outbreaks of influenza in pigs from infection with swine influenza A viruses are common. In addition, pigs are uniquely susceptible to infection with influenza viruses of human, swine, and avian origin. Because of this, pigs also can serve as hosts in which influenza viruses from different species can change by undergoing reassortment if a pig is infected with two or more different influenza A viruses at the same time. (Pigs are only infected with influenza A viruses.) Reassortment is a process in which influenza viruses exchange genes during replication. The resultant new hybrid influenza A virus could be highly transmissible among animals and to people, possibly leading to an influenza pandemic.
Interspecies influenza virus infections between people and pigs are most likely to occur when people are in close proximity to pigs, such as in swine production barns. Minimizing the transmission of influenza viruses between pigs and people can protect the health of swine workers and is in the best interest of animal and human public health.
The Centers for Disease Control and Prevention coordinates surveillance of influenza among humans with close collaboration from state, local, and territorial health departments.
USDA’s Animal and Plant Health Inspection Service (APHIS), coordinates surveillance of influenza among pigs through the National Swine Influenza Virus (SIV) Surveillance Program. More information about influenza surveillance in swine, including a Swine Procedures Manual, is available at Influenza Surveillance in Swine.
Recognizing the Signs of Influenza in Pigs
People who work with swine should be trained to recognize the signs of influenza in pigs. Typically illness is mild and a combination of signs can occur in infected swine. Signs of influenza in pigs can include any of the following:
- sudden onset of fever
- lethargy, lack of alertness
- going off feed (poor appetite)
- coughing (barking)
- discharge from the nose or eyes, eye redness or inflammation
- breathing difficulties
If pigs exhibit these signs, even mildly, appropriate veterinary care should be provided and preventive measures should be implemented by people working with or in close contact with ill pigs.
Preventing Transmission of Swine Influenza Viruses from Pigs to People
Influenza viruses are thought to spread from infected pigs to people primarily via large infectious droplets expelled by a sick infected pig during coughing or sneezing to a person in close contact with infected pigs. There also is indirect evidence to suggest that swine influenza viruses can be transmitted to people through contact with infected pigs or with surfaces recently contaminated with swine influenza viruses (e.g. touching pigs or handling material contaminated with pig secretions or feces, and then touching one’s mucous membranes). A third possible mode of transmission is via inhalation of small particulates containing swine influenza virus. The relative contributions of these three modes of transmission to the spread of swine influenza viruses to humans are not fully understood.
Basic Infection Control to prevent transmission of swine influenza viruses from pigs to people:
- Workers should adhere to recommendations for use of personal protective equipment (PPE).
- Hand hygiene should be performed after contact with animals or their environment, equipment and surfaces that are possibly contaminated with swine influenza viruses, and after removing personal protective equipment (PPE) and/or possibly contaminated clothing. Good hand hygiene should consist of washing with soap and water for 20 seconds or the use of other standard hand-disinfection procedures as specified by state government, or industry to limit the possibility of transmission of influenza viruses and other pathogens. Workers should avoid touching or rubbing their eyes, nose, and mouth when working around pigs.
- Vaccination of pigs with swine influenza vaccine that is effective against circulating strains in pigs might reduce the risk of influenza in pigs and possibly reduce the risk of people getting infected with swine influenza viruses. However, because multiple strains of swine influenza viruses might be co-circulating among the U.S. pig population and because swine influenza vaccines in pigs are not 100% effective, vaccination of pigs will not eliminate the risk of human infection from swine influenza viruses.
Personal Protective Equipment (PPE)
Swine workers should wear PPE whenever they might be exposed to pigs possibly infected with swine influenza viruses. Adherence to PPE recommendations might lessen a worker’s exposure to swine influenza A viruses and might reduce the chances of carrying contaminated material outside the barn or work site. Workers should be provided with appropriate PPE and instructions and training in PPE care and use. PPE should include fit-tested respirators to reduce inhalation exposure to small particles that might contain influenza viruses (1). National Institute for Occupational Safety and Health (NIOSH)-certified respirators are the only type of PPE that has been demonstrated to protect workers from general inhalation hazards.
Swine workers should adhere to the following practices:
- Wear protective clothing, preferably disposable outer garments or coveralls that are laundered at work after each use. To minimize risk of heat stress, wear lightweight clothing beneath protective clothing when appropriate.
- Wear rubber or polyurethane boots that can be cleaned and disinfected or disposable protective shoe covers.
- Wear disposable gloves made of lightweight nitrile or vinyl or heavy duty rubber work gloves that can be disinfected.
- To protect against dermatitis, which can occur from prolonged exposure of the skin to moisture in gloves caused by perspiration, wear a thin cotton glove inside the external glove.
- Change gloves if they are torn or otherwise damaged.
- Remove gloves promptly after use, before touching non-contaminated items or environmental surfaces.
- Take off disposable gloves by turning them inside out over the hand and placed in the trash after use.
- Wash hands after gloves and other PPE are removed.
- Wear safety goggles to protect the mucous membranes of eyes.
- Wear disposable NIOSH-certified filtering facepiece respirators (e.g., N-95 filtering facepiece respirator) or higher level of protection (e.g. P-100 or N-100 filtering facepiece respirators). These levels of respiratory protection might already be in use in workers at swine operations due to other hazards that exist in the environment (e.g., dusts). Workers must be fit tested to the respirator model that they will wear and also know how to check the facepiece-to-face seal. Workers who cannot wear a disposable NIOSH-certified filtering face piece respirator because of facial hair or other fit limitations should wear a loose-fitting (i.e., helmeted or hooded) powered air purifying respirator (PAPR) equipped with high-efficiency filters.
- Wear disposable, lightweight head or hair covers to prevent contamination of hair if shower-out facilities are unavailable.
- Discard disposable PPE properly, as well as clean and disinfect non-disposable PPE as specified in state government, industry, or USDA outbreak-response guidelines (e.g. non-disposable clothing should be laundered daily or after each use).
- Enforce biosecurity measures and practices to prevent the introduction of infectious agents from one swine housing unit to another. More information on disinfectant use and a list of antimicrobial products registered for use against influenza viruses can be found at the Environmental Protection Agency’s website.
- Shower-out, if facilities are available, into a clean area at the completion of an employee’s shift. If these facilities are not available, workers should change into clean clothes after their shift. Launder work clothes at the site or place in a plastic bag for washing separately from non–work family laundry.
- Wash hands thoroughly for 20 seconds with soap and water after removal of any PPE and/or contact with infected animals or possibly contaminated surfaces.
1Respirators should be used in the context of a comprehensive respiratory protection program as required by the Occupational Safety and Health Administration’s Respiratory Protection standard (29 CFR 1910.134). This includes training, medical evaluation, and fit-testing to ensure appropriate selection and use of NIOSH-certified respirators. To be effective, respirators must provide a proper sealing surface on the wearer’s face. Detailed information on respiratory protection programs is provided at OSHA and .
Surveillance and Monitoring of Workers’ Health
Instruct workers to watch for influenza-like illness signs and symptoms for 7 days after exposure to pigs that are suspected or known to be ill with influenza. The signs and symptoms of illness caused by swine influenza A virus infection in people are similar to the signs and symptoms of seasonal influenza. These can include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills, fatigue, and possibly diarrhea and vomiting.
Employers should consider making arrangements for appropriate medical follow up and treatment so that ill workers can take the following steps:
- Notify their supervisor and their employer’s health and safety representative that they are ill.
- Seek medical care
- The employer should arrange for health care and should notify the health care provider of the worker’s recent exposure to pigs.
- The medical care provider will decide if testing is needed. This could include collecting a nasal swab and a throat swab (which is best to do within the first 4 to 5 days of getting sick to be most likely to accurately diagnose influenza) for influenza testing.
- The medical provider might prescribe an antiviral medication to treat influenza which should be taken for five days. Antiviral medications for influenza treatment work best if started as soon as possible after illness develops, and ideally within 2 days after illness develops.
- Avoid travel and limit contact with other people and pigs as much as possible. Stay home for at least 24 hours after fever is gone (without requiring the use of fever reducing medications) except to get medical care or for other necessities.
- Practice good respiratory and hand hygiene to lower the risk of transmission of swine influenza virus to close contacts.
- Cover mouth and nose with a tissue when coughing or sneezing and put used tissue in a waste basket.
- If tissues are not available, cough or sneeze into the upper sleeve.
- Always wash hands after coughing or sneezing.
- More information about appropriate respiratory and hand hygiene is available on CDC’s “Cover Your Cough” website.
Clinicians taking care of patients who have signs and symptoms consistent with influenza and who had recent exposure to pigs should consult with their local or state health department to coordinate testing for swine influenza viruses. For more information on testing for influenza, see CDC’s Clinical Description & Lab Diagnosis of Influenza.
Persons at Higher Risk for Complications from Influenza
Certain groups are at increased risk of becoming severely ill with seasonal influenza, and are assumed to also be at increased risk for developing complications from swine influenza virus A infection. These groups include children younger than 5 years (but especially children younger than 2 years), persons 65 years and older, and pregnant women. Also included are persons of any age who have certain medical conditions such as chronic pulmonary disease, including asthma, or cardiovascular, hepatic, hematologic, neurologic, or metabolic disorders, such as diabetes, and persons who are immunosuppressed (including those immunosuppressed because of medications or HIV). People who fall into one or more of these groups can choose to request temporary reassignment to lower-risk tasks to avoid direct animal contact during outbreaks of suspected or confirmed influenza in pigs.
Administration of Influenza Antiviral Drugs
CDC’s website provides additional guidance for clinicians about influenza antiviral treatment and chemoprophylaxis. Influenza antiviral medications can be used for treatment of influenza, including illness caused by human infection with swine influenza viruses.
Antiviral chemoprophylaxis can be considered for workers in direct contact with pigs confirmed to have influenza. Chemoprophylaxis consists of taking an antiviral drug daily for the duration of time the worker is exposed to sick pigs, and for 5 to 7 days after the last known exposure.
Preventing Spread of Influenza Viruses from Workers to Pigs
Seasonal influenza viruses are occasionally transmitted from ill people to pigs. Therefore, workers should be educated on the need to prevent the spread of influenza viruses from ill persons to pigs. Workers also should be trained to recognize influenza-like illness signs and symptoms in humans. These include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills, fatigue, and possibly vomiting or diarrhea. A worker who has been diagnosed with influenza, or has similar influenza-like illness symptoms, or reports contact with others who have similar illness (listed above) should avoid contact with pigs. If the worker is essential to the operation and must enter the facilities, enforce their use of properly fitted, valve-less N95 respirators, gloves and other personal protective equipment (PPE) while on the farm. Biosecurity measures and practices (e.g. shower-in/shower-out procedures, PPE, disinfectant footbaths) to prevent the introduction of infectious agents into a swine operation also should be enforced. Recommendations from the Occupational Safety and Health Administration (OSHA) are available in a fact sheet entitled Occupational Safety and Health Administration (OSHA): Influenza in Workers and Pigs: Guidance for Commercial Swine Farmers and Pork Producers [1.6 MB, 2 pages].
Influenza Vaccination of Swine Workers
CDC recommends that everyone aged 6 months and older receive annual seasonal influenza vaccination. This is especially important for persons at higher risk for complications from influenza and household contacts of those persons. Vaccination with seasonal influenza vaccine is unlikely to protect against infection with swine influenza A viruses because these may be substantially different from the human influenza A viruses in the vaccine. However, influenza vaccination of swine workers – regardless of whether or not they have a high risk condition – is important to reduce the risk of transmitting seasonal influenza viruses from ill people to pigs. Seasonal influenza vaccination of workers might also decrease the potential for people or pigs to become co-infected with both human and swine influenza viruses. Such dual infections could result in genetic reassortment of the two different influenza A viruses and lead to a new influenza A virus that has a different combination of genes, and which could pose significant public health concern. Employers should consider providing swine workers with access to annual seasonal influenza vaccination that follow the recommendations for the general public for Preventing Seasonal Flu With Vaccination.
Adiego Sancho B, Omenaca Teres M, Martinez Cuenca S, Rodrigo Val P, Sanchez Villanueva P, Casas I, Pozo F, Perez Brena P. Human case of swine influenza A (H1N1), Aragon, Spain, November 2008. Euro Surveill. 2009 Feb 19;14(7). pii: 19120.
Centers for Disease Control and Prevention (CDC). Swine-origin influenza A (H3N2) virus infection in two children--Indiana and Pennsylvania, July-August 2011. MMWR Morb Mortal Wkly Rep. 2011 Sep 9;60(35):1213-5.
Centers for Disease Control and Prevention (CDC). Limited Human-to-Human Transmission of Novel Influenza A (H3N2) Virus — Iowa, November 2011. MMWR Dispatch;November 23, 2011 /60(Dispatch);1-3.
Cox CM, Neises D, Garten RJ, Bryant B, Hesse RA, Anderson GA, Trevino-Garrison I, Shu B, Lindstrom S, Klimov AI, Finelli L. Swine influenza virus A (H3N2) infection in human, Kansas, USA, 2009. Emerg Infect Dis. 2011 Jun;17(6):1143-4.
Dawood FS, Dong L, Liu F, Blau DM, Peebles PJ, Lu X, Wagers L, Oakland B, Zielenski M, Daly R, Horan V, Swenson SL, Schmitt BJ, Hancock K, Katz JM, Bridges C, Kightlinger L, Finelli L. A pre-pandemic outbreak of triple-reassortant swine influenza virus infection among university students, South Dakota, 2008. J Infect Dis. 2011 Oct 15;204(8):1165-71.
Forgie SE, Keenliside J, Wilkinson C, Webby R, Lu P, Sorensen O, Fonseca K, Barman S, Rubrum A, Stigger E, Marrie TJ, Marshall F, Spady DW, Hu J, Loeb M, Russell ML, Babiuk LA. Swine outbreak of pandemic influenza A virus on a Canadian research farm supports human-to-swine transmission. Clin Infect Dis. 2011 Jan 1;52(1):10-8.
Garten RJ, Davis CT, Russell CA, Shu B, Lindstrom S, Balish A, Sessions WM, Xu X, Skepner E, Deyde V, Okomo-Adhiambo M, Gubareva L, Barnes J, Smith CB, Emery SL, Hillman MJ, Rivailler P, Smagala J, de Graaf M, Burke DF, Fouchier RA, Pappas C, Alpuche-Aranda CM, López-Gatell H, Olivera H, López I, Myers CA, Faix D, Blair PJ, Yu C, Keene KM, Dotson PD Jr, Boxrud D, Sambol AR, Abid SH, St George K, Bannerman T, Moore AL, Stringer DJ, Blevins P, Demmler-Harrison GJ, Ginsberg M, Kriner P, Waterman S, Smole S, Guevara HF, Belongia EA, Clark PA, Beatrice ST, Donis R, Katz J, Finelli L, Bridges CB, Shaw M, Jernigan DB, Uyeki TM, Smith DJ, Klimov AI, Cox NJ. Antigenic and genetic characteristics of swine-origin 2009 A(H1N1) influenza viruses circulating in humans. Science. 2009 Jul 10;325(5937):197-201.
Gray GC, McCarthy T, Capuano AW, Setterquist SF, Olsen CW, Alavanja MC. Swine workers and swine influenza virus infections. Emerg Infect Dis. 2007 Dec;13(12):1871-8.
Gray GC, Baker WS. The importance of including swine and poultry workers in influenza vaccination programs. Clin Pharmacol Ther. 2007 Dec;82(6):638-41.
Gray GC, Baker WS. Editorial commentary: the problem with pigs: it's not about bacon. Clin Infect Dis. 2011 Jan 1;52(1):19-22. Karasin AI, Carman S, Olsen CW. Identification of human H1N2 and human-swine reassortant H1N2 and H1N1 influenza A viruses among pigs in Ontario, Canada (2003 to 2005). J Clin Microbiol. 2006 Mar;44(3):1123-6.
Myers KP, Olsen CW, Setterquist SF, Capuano AW, Donham KJ, Thacker EL, Merchant JA, Gray GC. Are swine workers in the United States at increased risk of infection with zoonotic influenza virus? Clin Infect Dis. 2006 Jan 1;42(1):14-20.
Myers KP, Olsen CW, Gray GC. Cases of swine influenza in humans: a review of the literature. Clin Infect Dis. 2007 Apr 15;44(8):1084-8Newman AP, Reisdorf E, Beinemann J, Uyeki TM, Balish A, Shu B, Lindstrom S, Achenbach J, Smith C, Davis JP. Human case of swine influenza A (H1N1) triple reassortant virus infection, Wisconsin. Emerg Infect Dis. 2008 Sep;14(9):1470-2.
Neumann G, Noda T, Kawaoka Y. Emergence and pandemic potential of swine-origin H1N1 influenza virus. Nature. 2009 Jun 18;459(7249):931-9.
Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team, Dawood FS, Jain S, Finelli L, Shaw MW, Lindstrom S, Garten RJ, Gubareva LV, Xu X, Bridges CB, Uyeki TM. Emergence of a novel swine-origin influenza A (H1N1) virus in humans. N Engl J Med. 2009 Jun 18;360(25):2605-15.
Ramirez A, Capuano AW, Wellman DA, Lesher KA, Setterquist SF, Gray GC. Preventing zoonotic influenza virus infection. Emerg Infect Dis. 2006 Jun;12(6):996-1000.
Shinde V, Bridges CB, Uyeki TM, Shu B, Balish A, Xu X, Lindstrom S, Gubareva LV, Deyde V, Garten RJ, Harris M, Gerber S, Vagasky S, Smith F, Pascoe N, Martin K, Dufficy D, Ritger K, Conover C, Quinlisk P, Klimov A, Bresee JS, Finelli L. Triple-reassortant swine influenza A (H1) in humans in the United States, 2005-2009. N Engl J Med. 2009 Jun 18;360(25):2616-25.
Shu B, Garten R, Emery S, Balish A, Cooper L, Sessions W, Deyde V, Smith C, Berman L, Klimov A, Lindstrom S, Xu X. Genetic analysis and antigenic characterization of swine origin influenza viruses isolated from humans in the United States, 1990-2010. Virology. 2011 Nov 10. [Epub ahead of print]
Terebuh P, Olsen CW, Wright J, Klimov A, Karasin A, Todd K, Zhou H, Hall H, Xu X, Kniffen T, Madsen D, Garten R, Bridges CB. Transmission of influenza A viruses between pigs and people, Iowa, 2002-2004. Influenza Other Respi Viruses. 2010 Nov;4(6):387-96. doi: 10.1111/j.1750-2659.2010.00175.x. Epub 2010 Oct 8.
United States Department of Agriculture. Influenza Virus Surveillance in Swine Program Overview for Veterinarians [1.9 MB, 2 pages].