In the United States, flu activity usually peaks between December and February, but cases can occur as early as October and as late as May.
Influenza A and B viruses are the primary cause of seasonal cases. Influenza A viruses are further classified into subtypes (e.g., A(H1N1), A(H3N2)).
Everyone 6 months of age and older is recommended to receive an annual flu vaccine, with a few exceptions:
Those who have had an allergic reaction after a previous dose on influenza vaccine, has any severe life-threatening allergies, or has ever had Guillain-Barré Syndrome (GBS) should not receive the Influenza (inactivated) vaccine
Those who are younger than 2 years or older than 49 years of age, are pregnant, has had an allergic reaction after a previous dose of influenza vaccine or any severe life-threatening allergies, children who are receiving aspirin or aspirin- or salicylate- containing products, have a weakened immune system, children who are between the ages of 2 and 4 years who have asthma or a history of wheezing in the last 12 months, children 5 years or older who have asthma, have taken influenza antiviral medication in the past 3 weeks, severely immunocompromised people, do not have a spleen or a non-functioning spleen, have a cochlear implant, have a cerebrospinal fluid leak, or have had GBS within 6 weeks after a previous dose of influenza vaccine should not receive the Influenza (live) vaccine.
Get your flu shot. Annual influenza vaccination is the most effective way to reduce influenza risk among healthcare personnel and patients.
Implement standard and droplet precautions for the duration of illness. Place patients in private rooms when available or cohort those with the same diagnosis.
Wear a face covering within 6 feet of a patient with suspected or confirmed flu, use gloves and gowns when exposure to respiratory droplets is likely, and perform hand hygiene before and after all patient contact.
No. Exclude healthcare personnel with influenza-like illness until at least 24 hours after fever has resolved without the use of fever-reducing medication.
Testing
Rapid molecular assays and RT-PCR are preferred for higher sensitivity and specificity compared to rapid antigen tests. Specimens should be collected prior to antiviral medication administration.
No. Start antiviral treatment as soon as possible for high-risk patients and those with severe illness – do not wait for test results.
Limit visitors to those essential for patient support. Ask them to wear a face covering, practice hand hygiene, and avoid visiting if they have respiratory symptoms.
Clinical specimens suspected of containing influenza viruses should be handled under Biosafety Level 2 (BSL-2) conditions, with standard precautions to prevent exposure.
Yes. Novel or highly pathogenic strains (e.g., avian influenza) may require BSL-3 practices or additional enhancements. Follow CDC and your facility’s biosafety committee guidance.
A nasopharyngeal swab in viral transport medium (VTM) is preferred. Some laboratories also accept combined nasal/oropharyngeal swabs or lower respiratory specimens.
Rigid outer packaging with appropriate labeling and UN 3373 marking
RT-PCR is the gold standard for influenza typing and subtyping. Some labs also use rapid molecular assays, viral culture, or immunofluorescence depending on capacity.
No. Report type and positivity results as soon as available; forward subtyping data when complete.
Not typically. Virus isolation should be performed only in appropriate facilities for specialized purposes.
