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\nFor information on the most recent avian influenza developments specific to the United States, please visit the Current Situation Summary page.
\nThis document provides guidance for follow-up and antiviral chemoprophylaxis of close contacts of cases of human infection with novel influenza A viruses associated with severe human disease or with the potential to cause severe human disease.
\nThis interim guidance is based on expert opinion and currently available published and unpublished data for antiviral treatment and chemoprophylaxis of seasonal, pandemic, and novel influenza A virus infections. These recommendations are based on the following considerations:
\nThe public health goal of this interim guidance is to prevent further spread of novel influenza A viruses associated with severe human disease if there are infected persons in the United States. It is specific to a scenario where there are sporadic cases associated with infected domestic poultry or wild bird exposures, and there is concern for possible limited, non-sustained human-to-human virus transmission.
\nClose contacts are defined as persons within approximately 6 feet (2 meters) or within the room or care area of a confirmed or probable novel influenza A case-patient for a prolonged period of time, or who had direct contact with infectious secretions while the case-patient was likely to be infectious (beginning 1 day prior to illness onset and continuing until resolution of illness). 2
\nIn general, decisions to initiate antiviral chemoprophylaxis should be guided by the risk stratification described below,3 based on observational data for reported cases of human infections with avian influenza A(H7N9) and A(H5N1) viruses, and on data from seasonal influenza studies. The risk of infection following close contact with a confirmed or probable novel influenza A case-patient is higher for persons with prolonged, unprotected exposures (e.g., without use of respiratory and eye protection) than for close contacts (e.g., health care personnel) who were wearing recommended personal protective equipment. More information: Recommended Personal Protective Equipment (PPE) [2.9 MB, 3 pages] and Interim Guidance for Infection Control Within Healthcare Settings.
\nHealth care personnel with unprotected close contact to case-patients with novel influenza A virus infection may have higher risk exposures than others through caring for patients of greater illness severity and higher viral levels. Persons with prolonged unprotected exposures outside of a healthcare facility may have a higher risk of exposure than those with short duration of close contact with a mildly ill novel influenza case-patient. Persons with an unprotected exposure to novel influenza A virus associated with severe human disease in a laboratory setting may have a high-risk or moderate-risk exposure, and need to be evaluated case by case.
\nPublic health personnel should attempt to identify as soon as possible and monitor all close contacts of confirmed or probable cases of human infection with novel influenza A viruses associated with severe human disease for new illness. (Visit Avian Influenza A Virus Case Definitions.) Available data suggest that the estimated incubation period for human infection with avian influenza A(H5N1) and A(H7N9) viruses is generally 3 to 5 days, but has been reported to be 7-10 days [1-12]. Limited non-sustained person-to-person transmission of A(H7N9) virus could not be excluded in some family clusters [7]. Limited non-sustained person-to-person transmission of A(H5N1) virus has been reported in several countries following close, prolonged unprotected contact with a severely ill A(H5N1) patient, including in household and hospital settings [6, 10, 11].
\nIdentified close contacts should be monitored daily for 10 days after the last known exposure to a confirmed or probable case. Measured temperature and presence of respiratory symptoms should be assessed daily during this period. Any close contacts of a confirmed or probable case with a measured temperature of \u226538.0\u00b0C (\u2265100.4\u00b0F) or any new respiratory symptoms (e.g., cough, sore throat, shortness of breath, difficulty breathing) should be referred for prompt medical evaluation and testing for novel influenza A virus infection. To facilitate investigation, and if resources are available, close contacts of cases under investigation (especially those with a high index of suspicion) also may be identified and monitored for fever and respiratory symptoms while the results of laboratory testing are pending.
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\nCDC will provide updated information as it becomes available on the CDC website at the Avian Influenza Current Situation Summary and Avian Influenza: Information for Health Professionals and Laboratorians.
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\n1 This guidance is intended to address human infections with novel influenza A viruses that cause severe or progressive disease in otherwise healthy persons resulting in hospitalization and/or death. A number of different subtypes of novel influenza A viruses have been reported to cause severe pneumonia and death, including A(H5N1), A(H5N6), A(H7N7), A(H7N9), A(H9N2), A(H10N3), A(H10N8), and A(H1N1v) and A(H3N2v) viruses; however, in recent years avian influenza A(H5N1), A(H5N6) and A(H7N9) virus infections have caused severe illness in a high proportion of cases and have been reported in substantial numbers.
\n2 Limited data are available regarding the risk of transmission for novel influenza A viruses; however, limited non-sustained person-to-person transmission of A(H5N1) virus has been demonstrated only with close, prolonged, unprotected exposure to a symptomatic A(H5N1) patient either at home or in a hospital [6, 10, 11], and limited non-sustained person-to-person transmission of A(H7N9) virus could not be excluded in some family clusters [7]. To define a close contact, this document uses \u201cwithin approximately 6 feet of an ill person\u201d to include the potential for transmission by large droplets or small particle droplet nuclei within the vicinity of the patient. Three feet has often been used by infection control professionals to define close contact and is based on studies of respiratory virus infections; however, for practical purposes, this distance may range up to 6 feet or more. The World Health Organization defines close contact as \u201capproximately 1 meter;\u201d the U.S. Occupational Safety and Health Administration uses \u201cwithin 6 feet.\u201d For consistency with infection control recommendations for healthcare settings, this document also defines \u201cwithin the room or care area of a novel influenza A patient\u201d as close contact for a health care provider or caregiver.
\n3 Exposure groups adapted from the stratification of risks for human infection with avian influenza A(H5N1) virus from the \u201cWorld Health Organization Rapid Advice Guidelines on pharmacological management of humans infected with avian influenza A (H5N1) virus, 2006\u201d (https://www.who.int/medicines/publications/WHO_PSM_PAR_2006.6.pdf)
\n4 Recommendations for special situations (e.g., travelers potentially exposed to novel influenza A viruses during air travel) will be made in the setting of specific contact investigation protocols.
\n5 Oral oseltamivir is approved by the FDA for treatment of acute uncomplicated influenza with twice-daily dosing for 5 days in persons 14 days old, and for prophylaxis with once-daily dosing in persons 1 year and older. Although use of oral oseltamivir for treatment of influenza in infants less than \u226514 days old, and for chemoprophylaxis in infants less than 1 year of age, are not part of the FDA-approved indications, these uses are recommended by the CDC and the American Academy of Pediatrics. Inhaled zanamivir is approved for treatment of acute uncomplicated influenza with twice-daily dosing in persons aged 7 years and older, and for prophylaxis with once-daily dosing in persons aged 5 years and older. Because this guidance recommends chemoprophylaxis using the twice-daily dosing studied in clinical trials of influenza treatment rather than the once-daily dosing studied in clinical trials supporting approval for influenza prophylaxis, it is recommended that inhaled zanamivir be used only in persons aged 7 years and older. Oral baloxavir (single-dose) is approved by FDA for treatment of acute uncomplicated influenza within 2 days of illness onset in persons aged 12 years and older, and for post-exposure chemoprophylaxis (single-dose) of influenza in persons aged 12 years and older.
\nTable. Follow-up and chemoprophylaxis recommendations according to the case definition category for human infection with novel influenza A viruses associated with severe disease. (Case Definitions for Investigations of Human Infection with Avian Influenza A Viruses in the United States)
\nConfirmed Case
\nAvian influenza A virus infection in a person that is confirmed by CDC\u2019s Influenza Division Laboratory or a CDC designated laboratory using methods mutually agreed upon by CDC and the Council of State and Territorial Epidemiologists (CSTE).
\nMonitor for fever and respiratory symptoms for 10 days after the last exposure to the confirmed case; Consider antiviral chemoprophylaxis based on risk of exposure2
\nSuspected Case (also called Case under investigation)
\nA person meeting criteria for avian influenza A virus infection below and for whom confirmatory laboratory test results are unknown or pending.
\nProbable case
\nA person meeting criteria for avian influenza A virus infection below and for whom laboratory test results do not provide a sufficient level of detail to confirm HPAI A H5 virus infection.
\nMonitor for fever and respiratory symptoms for 10 days after the last exposure to the probable case;
Consider antiviral chemoprophylaxis based on risk of exposure2
1 For specific dosage recommendations for chemoprophylaxis by age group, please visit https://www.cdc.gov/flu/professionals/antivirals/antiviral-dosage.htm.
2 Among close contacts: (1) Highest-risk exposure groups (recognized risk of transmission): Household or close family member contacts of a confirmed or probable case. (2) Moderate-risk exposure groups (unknown risk of transmission): Health care personnel with unprotected contact with a confirmed or probable case. (3) Low-risk exposure groups (transmission unlikely): Others who have had social contact of a short duration with a confirmed or probable case in a non-hospital setting (e.g., in a community or workplace environment)3