![]() Evaluation should be guided by symptoms and may include:.Consider evaluation if there is no improvement within 3–5 days of symptom onset.Clinical deterioration after initial improvement.Evaluate for coinfection (e.g., bacterial superinfection, and/or complications) if any of the following are present:.Normal or slightly elevated inflammatory markersĬonsider bacterial coinfection in patients with elevated inflammatory markers (e.g., CRP). ![]() Blood tests are not routinely indicated, but if performed, may show:.Serologic testing and viral cultures: not recommended for diagnosis.Only indicated if more sensitive tests are unavailable.High specificity but limited sensitivity.Rapid antigen test: can detect various influenza A/B antigens, usually via nasal or pharyngeal swabs.Rapid molecular assay: preferred test for outpatients.Molecular assays are the preferred method for detecting influenza virus infection.Hospitalization for acute respiratory illness and potential exposure to the influenza virus.Onset of acute respiratory symptoms during hospital stay.Hospitalization for acute respiratory illness or worsening of chronic cardiopulmonary disease.Consider for febrile patients with acute respiratory illness (especially those at high risk for complications of influenza).Consider for patients with any respiratory symptoms who are likely to be discharged home.Worsening of chronic cardiopulmonary disease.Acute onset of respiratory symptoms and one of the following:.Patients at high risk for complications of influenza with any respiratory symptoms.Small shifts in a panda's habitat can cause epic dread: Shifts can cause pandemics and drifts cause epidemics. Causes epidemics (limited to a specific population or region).Does not alter the subtype (e.g., H5N1 or “ avian flu”).Minor changes in antigenic structure ( hemagglutinin and/or neuraminidase) via random point mutation.Causes pandemics (limited to a specific time period).Occurs in particular when human pathogenic and animal pathogenic influenza viruses exchange genetic information.Two subtypes of viruses (e.g., human and swine influenza) infect the same cell and exchange genetic segments ( reassortment) to create new subtypes ( e.g., H3N1 → H2N1).Host cell dies → cellular breakdown triggers a strong immune response.Viral neuraminidase (N) cleaves the neuraminic acid → virions exit the cell.The new virus particles travel to the cell membrane → formation of a membrane bud around the virus particles ( budding).The virus replicates in the nucleus of the cell.Viral hemagglutinin (H) binds sialic acid residues (neuraminic acid derivatives) on the host cell membrane → virus fusion with the membrane → entry into the cell.Influenza viruses bind to the respiratory tract epithelium.Hand hygiene, respiratory hygiene, and vaccination can help prevent the spread of influenza. Rarely, patients may develop secondary bacterial pneumonia, most commonly caused by Staphylococcus aureus or Streptococcus pneumoniae. Antiviral therapy may reduce the severity and shorten the duration of symptoms, and reduce the risk of developing complications. However, antiviral therapy may be considered for patients with early or severe disease, especially in those at high risk for complications. Usually, symptoms are self-limited and supportive treatment is sufficient. The diagnosis can often be established based on clinical presentation, but PCR testing may be used to confirm the diagnosis. Inflammatory markers are usually normal or slightly elevated. Symptomatic patients may present with sudden onset of high fever, headache, myalgias, arthralgias, nonproductive cough, and malaise. Influenza viruses frequently mutate, resulting in the emergence of new subtypes and strains. There are various subtypes of influenza A viruses, which are classified based on their hemagglutinin (H) and neuraminidase (N) surface antigens. It is caused by influenza A, B, and C viruses. Influenza is a highly contagious viral infection that typically occurs during the winter months.
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