This is an official CDC HEALTH advisory.
***Missouri health care providers in the city of St. Louis, please contact the City of St. Louis Department of Health or the Department of Health’s Office of Communicable Disease Control and Prevention and Missouri Senior Services (DHSS) at 573-751-6113 or 800-392-0272 (24/7) with questions regarding this CDC Health Advisory, to report a case of influenza in a patient who recently been exposed to pigs, or to request additional subtype-specific real-time polymerase chain reaction (RT-PCR) testing of influenza isolates at the Missouri State Public Health Laboratory.***
Summary
The Centers for Disease Control and Prevention (CDC) is issuing this Health Alert Network (HAN) health advisory to provide updates on recent infections with the variant influenza virus⸣ and summarize the CDC’s recommendations for the identification, treatment and prevention of variant influenza virus infection for summer and fall 2022.
Background
Five cases of human infection with influenza viruses that typically spread only in pigs, also known as variant influenza virus infections, were reported to the CDC in August 2022. These cases include three infections with variant influenza A(H3N2) (A(H3N2)v) virus and two infections with influenza A(H1N2)v virus. These cases have been identified in West Virginia (3), Oregon (1) and Ohio (1). Four of the five cases reported exposure to pigs or attendance at an agricultural fair prior to illness, and one reported no contact with pigs or attendance at an agricultural fair prior to illness. The clinical features of these cases are similar to those of seasonal influenza infections and include fever, cough, pharyngitis, myalgias and headache. No hospitalizations or deaths have occurred among these five cases, and all patients are recovering or have recovered from their illnesses. To date, no person-to-person spread associated with the five recent variants of influenza virus infection has been identified.
Early identification and investigation of influenza virus variants is important to determine if the virus is spreading effectively among people. Rapid detection and characterization of novel influenza A viruses and efforts to reduce transmission to others remain important components of national efforts to prevent the emergence of novel viruses that could have pandemic potential. To accomplish this, screening for influenza viruses and surveillance for new influenza A virus infections, including variants of influenza virus infection, should continue throughout the year.
People, especially those at increased risk of complications from influenza, can take public health measures to limit their risk of infection (eg, limit exposure to infected animals). Clinicians are encouraged to consider variant influenza virus infection as a possible diagnosis when evaluating patients with acute respiratory illness and exposure to pigs or agricultural fairs prior to illness.
Since 2005, 504 variants of influenza virus infection (of different influenza A virus subtypes) have been identified in the United States; most of these infections have been associated with exposure to pigs or attendance at an agricultural fair prior to illness onset. Agricultural fairs are held annually in the United States, primarily during the summer and early fall. Many fairs have pigsties, where pigs from different geographical areas come into close contact with each other and with people. These places can allow influenza viruses to spread among pigs and between pigs and humans. Infected pigs can spread influenza viruses even if they do not show symptoms (eg coughing or sneezing).
The CDC predicts that state health departments may identify more cases of infection with variant influenza viruses in 2022 as the agricultural fair season continues. Testing for variant influenza viruses should focus primarily on people whose exposure is known to be associated with infection with the variant influenza virus (for example, attendance at agricultural fairs or workers in the hog industry ). New influenza A virus infections, which include those caused by influenza virus variants, are reportable conditions in the United States, and all confirmed cases must be reported to the CDC within 24 hours.
Recommendations for Clinicians
- Outside of traditional influenza season, ask patients with suspected influenza if they have recently been exposed to pigs.
- Clinicians suspecting influenza in people with recent exposure to pigs should:
- Obtain a nasopharyngeal swab or aspirate from the patient,
- Place the swab or aspirate in viral transport medium, and
- Contact their state or local health department to arrange transportation and request prompt diagnosis at a state public health laboratory.
- Recommend antiviral therapy to patients with suspected or confirmed influenza variant virus infection who are hospitalized, have severe illness, or are in a group considered to be at increased risk for influenza complications². Antiviral treatment may also be considered for people who are not at increased risk based on clinical judgment and if treatment can be initiated within 48 hours of illness onset.
Recommendations for public health services and laboratory technicians
- Improve respiratory disease surveillance during the agricultural fair season to facilitate the timely detection and investigation of cases of influenza virus variants.
- Respiratory specimens from persons suspected of being infected with the influenza A variant virus should be collected and sent for subtype-specific real-time polymerase chain reaction (RT-PCR) testing in a laboratory state public health. Although commercially available influenza rapid diagnostic tests (RIDTs) and molecular influenza tests can reliably detect influenza A variant viruses, they cannot differentiate influenza A variant viruses from human influenza A viruses.
- Public health laboratories should immediately send influenza A virus specimens that cannot be subtyped or that are presumed positive for the influenza variant (using the methods described in the instructions for use of the test) to the CDC and submit all samples that are otherwise unusual as soon as possible after identification. Please email [email protected] to notify the CDC that you have a sample to submit.
Recommendations for the public
- People who are at higher risk of influenza complications² should avoid exposure to pigs and piggeries at fairs this year. If you cannot avoid exposure to pigs, you should wear a properly fitted mask that covers your nose and mouth and wash your hands frequently.
- All people should take precautions when engaging in activities that may involve contact with pigs. Precautions include hand hygiene before and after exposure to animals, avoiding eating or drinking in animal areas, and avoiding close contact with animals that look or act unwell.
- Patients with ILI who are at higher risk of influenza complications² should consult their healthcare provider as soon as possible after the onset of symptoms to determine if treatment with antiviral medications is warranted.
- Patients who experience flu-like symptoms from direct or close contact with pigs and seek medical attention should inform their healthcare provider of the exposure.
For more information
⸣Influenza viruses that circulate in pigs are called swine influenza viruses when isolated from pigs, but are called variant viruses when isolated from humans.
² This includes people with certain underlying chronic conditions such as asthma, diabetes, heart disease or neurological disorders, pregnant women and people aged 5 and under and 65 and over, or whose the immune system is weakened.
