infectious diseases
Influenza
Key Points
Minor antigenic drift in H and/or NA antigens produces strains that cause seasonal epidemics; rare antigenic shifts resulting in new combinations of H and NA antigens can cause a pandemic with significant mortality. Influenza itself may cause pneumonia, or patients with influenza may develop secondary bacterial pneumonia. Diagnosis is usually clinical, but sensitve and specific RT-PCR assays can differentiate influenza types and subtypes and thus help select antiviral therapy and determine whether outbreaks of respiratory disease are due to influenza. Treat most patients symptomatically. Antiviral drugs given early can slightly decrease duration and severity of symptoms but are typically used only in high-risk patients; different influenza types and subtypes are resistant to different drugs. Vaccinate annually everyone aged ≥ 6 months who does not have a contraindication; antiviral drugs can be used for prevention in immunocompromised patients (who may not respond to vaccination) and patients with contraindications to vaccination. 