Viral influenza affects 5 to 20 percent of Americans each year, according to the U.S. Centers for Disease Control and Prevention (CDC). In most people, influenza causes mild to moderate self-limited respiratory disease. In others, it can cause severe disease and even death, mainly from influenza-related complications. People at high risk for complications from viral influenza include those over age 65, children under 5 and especially under 2, pregnant women and people with chronic medical problems such as diabetes, heart disease and asthma.
Pneumonia
According to "Harrison's Principles of Internal Medicine," one of the most common complications of viral influenza is pneumonia. Pneumonia related to influenza may be a primary infection (caused by the virus itself), a secondary bacterial infection (caused by bacteria after the lungs are weakened by the virus) or a combination of the two. Regardless of the cause, pneumonia presents as influenza that gets worse instead of better.
The most common symptoms of pneumonia are cough, fever, shaking chills and trouble breathing, notes the American Lung Association. Additional symptoms include sharp or stabbing pain with inhalation, headache, sweating/clamminess and mental confusion, especially in the elderly. Cough that produces scant amount of clear or blood-tinged sputum signals viral pneumonia. Cough that produces copious amounts of sputum or green or yellow sputum is more consistent with bacterial pneumonia.
Reye's Syndrome
Reye's syndrome is a serious complication of viral influenza that has been described in children and teens treated with aspirin. According to MedlinePlus, the onset of Reye's syndrome usually follows a week after the infection has resolved. Symptoms start with vomiting that lasts for several hours. Vomiting is followed by aggressive and irritable behavior, then lethargy, loss of consciousness and seizures. Brain and liver damage may be permanent. Although "Harrison's Principles of Internal Medicine" reports that the incidence of Reye's syndrome has decreased as a result of widespread warnings against aspirin use in children with viral infections, parents should be aware of the danger.
Myositis & Rhabdomyolysis
Myositis and rhabdomyolysis are extremely rare complications of viral influenza, according to "Harrison's Principles of Internal Medicine." The term "myositis" refers to inflammation of the muscle fibers. Although muscle pain is a common symptoms of influenza, true myositis is very different. Patients with myositis complain of exquisite sensitivity to touch--particularly in the legs--often to the point that even the weight of bedsheets may be intolerable. In severe cases, the muscle fibers actually die, a condition known as rhabdomyolysis. Aside from permanent loss of muscle tissue, rhabdomyolysis often is associated with shock and kidney failure.
References
- Centers for Disease Control and Prevention: Seasonal Influenza
- "Harrison's Principles of Internal Medicine, 17th edition" - Influenza chapter; A.S. Fauci, E. Braunwald, D.L. Kasper, S.L. Hauser, D.L. Longo, J.L. Jameson, J. Loscalzo (eds.); 2009
- American Lung Association: Pneumonia
