Influenza

Influenza is typically characterized by the abrupt onset of fever, chills, headaches, severe myalgias (muscle pains), malaise, and loss of appetite. These are evident after an incubation period of one to two days. In the first three days of illness, headache and muscle pain are usually the most bothersome symptoms, with the severity of these complaints reflecting the magnitude of the fever. Dry cough, severe sore throat, and nasal obstruction and discharge are usually also present, although they may be overshadowed by the systemic complaints. The fever typically resolves after approximately three days, but the cough, sore throat, and hoarseness may persist for three to four days after the fever resolves. It is important to remember that in frail older adults disease presentation can be atypical. For example, some individuals might present only with fever, lack of energy, or confusion, and without any evidence of respiratory illness. Influenza should be considered in any illness characterized by fever in an elderly person during influenza season.

Without complications, influenza is a self-limited illness lasting five to eight days. Elderly patients and patients with high-risk medical conditions, including chronic lung or heart disease, kidney disease, problems with the immune system, cancer, or other chronic medical problems are at risk for developing complications from influenza. Pneumonia caused by the influenza virus itself and secondary bacterial pneumonia are the most common and serious complications of influenza. Patients with influenza pneumonia, a complication which is fortunately quite rare, will present with typical signs and symptoms of influenza but go on to develop severe cough, shortness of breath, and cyanosis. Chest X-rays will usually show bilateral findings most consistent with adult respiratory distress syndrome, and gram stains of sputum will not identify a bacterial pathogen. Death, due to diffuse hemorrhagic pneumonia, is high even with prompt antiviral therapy.

Secondary bacterial pneumonia is indistinguishable from community-acquired pneumonia in the absence of influenza, except that it typically occurs in elderly patients or patients with chronic heart or lung problems after recovery from a classic influenza illness. Patients will usually describe a recurrence of fever, cough, and sputum production four to fourteen days after their initial recovery from influenza. Physical examination and chest X-ray usually reveal a focal area of lung infection. Microbiological examination of the sputum often shows bacteria such as Streptococcus pneumoniae or Haemophilus influenzae. Treatment of community-acquired pneumonia as a secondary complication of influenza infection is not different than in any other setting, and requires antibiotic drugs.