Human infections with variant influenza viruses are not common but do sporadically occur, most commonly among people who have direct or frequent contact with pigs (e.g., workers in the swine industry or children near pigs at a fair). Unlike seasonal influenza viruses, which typically circulate widely during October–May, most variant influenza virus cases identified in the United States have occurred during summer months, when seasonal influenza virus activity is low.
Clinical Information
Illness in humans infected with a variant influenza virus is typically mild, with symptoms like those of seasonal influenza. Like seasonal influenza, severe illness resulting in hospitalization and death is possible. People at high risk of serious complications from seasonal influenza and variant influenza include children less than 5 years, adults 65 years and older, pregnant people, and people with certain chronic medical conditions like asthma, diabetes, heart disease, and weakened immune systems.
Variant influenza clinical guidance from CDC:
Public Health Preparation for Annual Agricultural Events
County, regional, and state agricultural fairs are locations where large numbers of people and pigs converge. The opportunity for transmission of variant influenza virus to people is enhanced if pigs with influenza infections are present.
Proactive consultation with fair managers and intervention by public health officials can identify and mitigate opportunities for contact between people and ill pigs.
Local health jurisdictions (LHJs) should be aware of upcoming agricultural fairs in their jurisdictions where pigs will be present and take the following actions, particularly if variant influenza cases have been identified in the area:
Remind providers to be alert for patients with fever ≥38.0° C (100.4° F) and respiratory symptoms, particularly if occurring outside of the regular influenza season. If such patients present for care, providers are recommended to:
Ask about recent (within 10 days of illness onset) contact with pigs (direct, e.g., touched a pig, or indirect, e.g., walked through a barn where pigs were or had been present).
Collect respiratory specimens for influenza testing by a public health laboratory (PHL) if patient had pig exposure (within 10 days of illness onset). For collection and shipping information, see VRDL Test Page - Novel/Avian Influenza Virus (human) PCR.
Provide agricultural officials and managers of fairs in your jurisdiction with disease prevention protocols for animal exhibitions, including monitoring for ill pigs.
Provide education about swine influenza and how to prevent transmission to humans to local 4-H and other youth or agricultural organizations that exhibit pigs at your county fair.
Public Health Response to Suspect, Probable, or Confirmed Variant Influenza Virus Infections
The focus of the public health response to suspected, probable, or confirmed variant influenza virus infections is case finding and identification of ill close contacts.
Testing Criteria
Situations of concern for variant influenza virus infections in humans that should prompt testing by a local PHL or the CDPH Viral and Rickettsial Disease Laboratory (VRDL):
Reports from healthcare providers or residents in your jurisdiction of fever and respiratory symptoms in a person with recent (within 10 days of symptom onset) direct or indirect (such as attendance at an agricultural fair) pig contact.
Reports of clusters of influenza A (or any influenza, if no influenza type information is available) from persons, healthcare providers, schools, camps, etc. within 10 days of a fair or other agricultural event in your jurisdiction where pigs were present.
Reports of respiratory illnesses in pigs at a fair or other agricultural event that are suspected or confirmed to be influenza in the presence of known symptomatic persons; local public health officials should initiate variant influenza case finding among humans.
Testing at a PHL is recommended for reports from clinical laboratories of influenza A positive specimens not known to be a seasonal influenza A subtype. For information on testing, see: VRDL Test Page - Novel/Avian Influenza Virus (human) PCR.
The following information should be obtained for suspect human cases:
Basic demographic information, the patient’s pig contact history, and illness severity should be provided to the COVID Control Branch and VRDL at the time the specimen is shipped to VRDL or a local PHL.
Days, times, and locations of pig exposure.
Knowledge of, or contact with, sick pigs.
Illness symptoms.
Health care received.
Influenza testing results.