infectious diseases
Influenza
Diagnosis of Influenza
Clinical evaluation Sometimes rapid antigen or conventional reverse transcriptase-polymerase chain (RT-PCR) tests Pulse oximetry and chest x-ray for patients with severe respiratory symptoms The diagnosis of influenza is generally made clinically in patients with a typical syndrome when influenza is known to be present in the community. Although many rapid diagnostic molecular tests (antigen detection tests) are available and most have good specificity, their sensitivities vary widely, and they usually add little to patient management. Diagnostic tests should be done when results will affect clinical decisions. Reverse transcriptase–polymerase chain reaction (RT-PCR) tests are sensitive and specific and can differentiate influenza types and subtypes. If this test is quickly available, results may be used to select appropriate antiviral therapy; it should also be done when influenza is suspected in hospitalized patients because antiviral treatment is usually indicated. Also, these tests can prevent the unnecessary use of antibacterial drugs, and identification of the specific influenza virus can be important for infection control. These tests are also useful to determine whether outbreaks of respiratory disease are due to influenza. Cell culture of nasopharyngeal swabs or aspirates takes several days and is not useful for patient management decisions. If patients have lower respiratory tract symptoms and signs (eg, dyspnea, rales noted during lung examination), pulse oximetry to detect hypoxemia and a chest x-ray to detect pneumonia should be done. Primary influenza pneumonia appears as focal or diffuse interstitial infiltrates or as Acute Hypoxemic Respiratory Failure (AHRF, ARDS) . Secondary bacterial pneumonia is more likely to be lobar or segmental. 