Interim Guidance on Influenza Antiviral Chemoprophylaxis of Persons Exposed to Birds with Avian Influenza A Viruses Associated with Severe Human Disease or with the Potential to Cause Severe Human Disease
For information on the most recent avian influenza developments specific to the United States, please visit the Current Situation Summary page.
This document provides interim guidance for clinicians and public health professionals in the United States on antiviral chemoprophylaxis of persons exposed to birds infected with avian influenza A viruses associated with severe human disease or thought to have the potential to cause severe human disease. Examples of viruses with the potential to cause severe human disease can be found on Bird Flu Virus Infections in Humans. Additionally, more information about specific avian influenza A viruses and past reported human infections with avian influenza A viruses is available. There is limited experience with these newly detected viruses to inform public health guidance regarding use of antiviral chemoprophylaxis. However, these viruses are thought to have the potential to infect people and cause severe illness. A small number of rare human infections with avian influenza A viruses have been documented in the U.S. since 2002. CDC will update this guidance as additional information becomes available.
Persons with recent exposure (within 10 days) to avian influenza A viruses include the following:
- Exposure to A(H5), A(H7), or A(H9) virus infected birds is defined as follows:
- Close exposure (within 2 meters) to birds, with confirmed avian influenza A virus infection by A(H5), A(H7), or A(H9) viruses. Bird exposures can include, but are not limited to handling, slaughtering, defeathering, butchering, culling, or preparation of birds for consumption; OR
- Direct contact with surfaces contaminated with feces or bird parts (e.g., carcasses, internal organs) from infected birds; OR
- Visiting a live poultry market with confirmed bird infections or associated with a case of human infection with avian influenza A virus.
- Exposure to an infected person – Close (within 2 meters) unprotected (without use of respiratory and eye protection) exposure to a person who is a confirmed, probable, or symptomatic suspected case of human infection with avian influenza A virus (e.g. in a household or healthcare facility).
- Laboratory exposure – Unprotected (without use of respiratory and eye protection) exposure to avian influenza A virus in a laboratory.
More information can be found on Case Definitions for Investigations of Human Infection with Avian Influenza A Viruses in the United States.
Infected refers to infection with avian influenza A viruses associated with severe human disease or which have the potential to cause severe human disease. The risk of infection with avian influenza A viruses is higher in people with unprotected exposures (e.g., not using respiratory and eye protection) than in those who used such protective equipment.
Persons with unprotected exposure (e.g., not using respiratory and eye protection) are included in the definition above and on Case Definitions for Investigations of Human Infection with Avian Influenza A Viruses in the United States.
It is not possible to know whether a well-appearing, sick or dead wild bird is infected with avian influenza A viruses until they are tested.
Exposed persons should monitor themselves daily for signs and symptoms of new illness for 10 days after the last known exposure. Signs and symptoms may include fever (temperature of 100ºF [37.8ºC] or greater) or feeling feverish, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, eye redness (or conjunctivitis), shortness of breath or difficulty breathing. Fever may not always be present. Less common signs and symptoms are diarrhea, nausea, vomiting, or seizures.
Any exposed person who has any new illness symptoms, particularly fever or feeling feverish or any respiratory symptoms should be referred for prompt medical evaluation, antiviral treatment, and testing for avian influenza A virus infection.
Chemoprophylaxis with influenza antiviral medications can be considered for exposed persons. Decisions to initiate post-exposure antiviral chemoprophylaxis should be based on clinical judgment, with consideration given to the type of exposure (e.g. without use of respiratory and eye protection), duration of exposure, time since exposure (e.g. less than 2 days), known infection status of the birds the person was exposed to, and to whether the exposed person is at higher risk for complications from seasonal influenza.
If post-exposure antiviral chemoprophylaxis is initiated, treatment dosing for the neuraminidase inhibitors oseltamivir or zanamivir (one dose twice daily) is recommended in these instances instead of the typical antiviral chemoprophylaxis regimen (once daily).4 For specific dosage recommendations for treatment by age group, please see Influenza Antiviral Medications: Summary for Clinicians. Physicians should consult the manufacturer’s package insert for dosing, limitations of populations studied, contraindications, and adverse effects. If exposure was time-limited and not ongoing, the recommended duration is five days (one dose twice daily), from the last known exposure. Chemoprophylaxis is not routinely recommended for personnel involved in culling non-infected or likely non-infected bird populations as a control measure for personnel involved in handling sick birds or decontaminating affected environments (including animal disposal) who used proper personal protective equipment.
1 The highly pathogenic avian influenza A(H5N1) viruses isolated from US wild aquatic birds and domestic poultry is genetically different from the highly pathogenic avian influenza A(H5N1) viruses that have caused sporadic human infections resulting in severe illness with high mortality in several other countries (notably in Asia and Africa).
2 This direct exposure may include: contact with birds (e.g., handling, slaughtering, defeathering, butchering, preparation for consumption); direct contact with surfaces contaminated with feces or bird parts (carcasses, internal organs, etc.); or prolonged exposure to birds.
3 The potential incubation period is unknown for avian influenza A viruses which are not yet known to cause human disease. Available data suggest that the estimated incubation period for human infection with A(H5N1) and A(H7N9) viruses is generally 3 to 5 days but has been reported to be as long as 7-10 days.
4 This recommendation for twice daily antiviral chemoprophylaxis dosing frequency is based on limited data that support higher chemoprophylaxis dosing in animals for avian A(H5N1) virus (Boltz DA, et al JID 2008;197:1315) and the desire to reduce the potential for development of resistance while receiving once daily dosing (Baz M, et al NEJM 2009;361:2296; Cane A et al PIDJ 2010;29:384; MMWR 2009;58:969).