Influenza
The flu syndrome is a severe illness, lasting from three days to two weeks with convalescence over one to four weeks. Symptoms include the abrupt onset of malaise, prominent
myalgia, headache and high fever (up to 106F, lasting three to seven days), followed by cough, rhinorrhea, pharyngitis and weakness. Complications include prolonged airway hyperreactivity, particularly in patients with asthma and chronic bronchitis. Secondary bacterial bronchitis and pneumonia are seen in up to ten percent of patients, and usually present as purulent or bloody sputum and increased fever after a few days of apparent clinical improvement. The most common cause is
Streptococcus pneumoniae, although
Hemophilus influenza and
Staphylococcus aureus infections (associated with a 50 percent mortality) are also seen. Rare nonpulmonary complications include myositis (with or without myoglobinuria and acute renal failure), Guillain-Barre syndrome, encephalitis, transverse myelitis and Reye's syndrome. Since the flu syndrome can be severe, patients who are elderly, debilitated by chronic disease, immuno- compromised or those with severe dehydration or secondary complications may require hospitalization.
While may viruses can cause "flu," including parainfluenza, respiratory syncytial virus and adenovirus, 85 percent of cases are caused by influenza A or B. Epidemic spread of the influenza virus is due to the appearance of new antigenic variations of the virus in nonimmune populations. Major antigenic variations lead to pandemics and minor antigenic changes cause the nearly annual winter epidemics. Viral transmission takes place through the aerosol route, by sneezing, coughing and talking; the virus has an extremely high attack rate.
Treatment of the flu consists of symptomatic and supportive care, including bed rest, hydration, analgesics, antipyretic agents and antibiotics for secondary bacterial infection. Amantadine and rimantadine are approved for the treatment of influenza A infections, but must be administered within the first 24 to 48 hours if they are to have any effect. In general, patients at high risk for morbidity and mortality who have the "flu syndrome" should be treated with these agents - unvaccinated patients with chronic pulmonary, cardiovascular, neuromuscular, metabolic and immunodeficiency diseases. It may also be appropriate to treat patients involved in critical jobs, such as policemen, firemen and selected health care personnel. Amantadine and rimantadine are not curative; they attenuate disease in patients with influenza A infection by shortening the duration of acute illness by one to two days and decreasing fever by 50 percent.
Given the potential severity of illness, prophylactic measures are recommended for select patients. Recommendations about vaccination are discussed in Chapter 3. Amantadine prophylaxis prevents clinical disease in 70 to 90 percent of patients and should be considered for the same high risk groups outlined above, particularly those in closed settings such as nursing homes.