According to the National Institutes of Health (NIH), 5 to 20 percent of the U.S. population is infected with influenza each year. The spectrum of disease associated with influenza ranges from mild, self-limited respiratory infection to fatal pneumonia. In addition to the classic symptoms, influenza infection is also associated with some uncommon side effects.
Bacterial Pneumonia
According to "Harrison's Principles of Internal Medicine," the influenza virus attacks the cells lining the respiratory tract. Even when the immune system successfully cleared the influenza infection, the battered airways are still vulnerable to attack by bacteria. In the most common scenario, a person begins to feel better only to feel suddenly worse a few days later. Symptoms of pneumonia include cough, fever, chills and difficulty breathing. Unlike the "dry" cough associated with flu, bacterial pneumonia results in cough productive of green or yellow sputum, often in copious amounts.
Exacerbation of Chronic Disease
Fighting the flu puts extra strain on the heart, lungs and immune system. In healthy people, this is usually not a problem. However, in the elderly and other individuals classified by the NIH as "high risk," the extra burden imposed by influenza infection can induce deterioration in cardiovascular, lung and kidney function. According to "Harrison's Principles of Internal Medicine," in some cases, this is reversible with a long hospital course and aggressive care. In other cases, however, changes are irreversible and lead to death.
Myositis and Rhabdomyolysis
Myositis and rhabdomyolysis are uncommon side effects of influenza infection. The NIH defines myositis as inflammation of the muscle fibers. People with influenza-related myositis may be exquisitely tender to touch--even bedsheets can become intolerable. The lower extremities are most commonly affected. Muscles may be swollen and "boggy" feeling.
In severe cases, myositis may be severe enough to induce spontaneous death of muscle fibers, a condition known as rhadomyolysis. Not only is muscle tissue permanently lost, the release of muscle breakdown products into the bloodstream usually results in acute kidney failure.
References
- National Institutes of Health Influenza Information
- Influenza (Chapter); R. Dolan; In: Harrison's Principles of Internal Medicine, 17th ed.; A.S. Fauci, E. Braunwald, D.L. Kasper, S.L. Hauser, D.L. Longo, J.L. Jameson, J. Loscalzo (eds.); 2009
- National Library of Medicine: Myositis Patient Information
