Influenza is typically a self-limited illness characterized by fever, dry cough, muscle aches, sore throat, fatigue, and sometimes nausea and vomiting. However, the flu can cause serious complications, especially in people with preexisting health problems. The Centers for Disease Control and Prevention (CDC) reports that roughly 200,000 Americans are hospitalized and 36,000 die annually of influenza-related complications.
Pneumonia and Bronchitis
Influenza is typically an upper respiratory illness. However, the virus may infect the airways lower in the lung, causing bronchitis or pneumonia. With bronchitis, the bronchial tubes are inflamed, which causes productive coughing and wheezing. Note that flu causes a dry cough, so the production of phlegm is a clue that something beyond the typical flu is occurring. Pneumonia is a serious complication of the flu. The deepest part of the lungs, the air sacs, are affected, causing diminished oxygen and carbon dioxide exchange. Productive cough and shortness of breath are typical symptoms. With both bronchitis and pneumonia associated with the flu, the cause may be the flu virus itself or a superimposed bacterial infection. People with chronic heart or lung disease, diabetes, a weakened immune system or another chronic illness are at increased risk for influenza-related pneumonia.
Sinus and Ear Infections
Flu typically causes swelling of the nasal and throat linings, which may block the openings to the sinuses and eustachian tubes (the connections between the upper throat and the ears). These blockages can lead to bacterial infections, specifically sinus or ear infections.
Chronic Lung Disease Aggravation
People with asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis or another chronic lung disease may experience worsening of their disease as a complication of the flu. For this reason, CDC recommends yearly flu vaccination for all people with chronic lung disease.
Heart Attack
People with heart disease are not only at increased risk of pulmonary complications from the flu, they are also at increased risk for a heart attack. In a 2009 review article, "Influenza as a Trigger for Acute Myocardial Infarction or Death from Cardiovascular Disease," published in The Lancet Infectious Diseases, Dr. Charlotte Warren-Gash reported there are consistent associations between influenza and increased heart attack risk.
Guillain-Barré Syndrome
Guillain-Barré syndrome is a rare disorder in which the immune system errantly attacks the nervous system. The syndrome typically begins with weakness and tingling of the legs, which spread to the trunk and arms. In the most severe cases, temporary total body paralysis may occur, requiring ventilator assistance. Full recovery over a period of days to weeks is the norm. Guillain-Barré syndrome can be triggered by the flu.
Reye's Syndrome
Reye's syndrome is an uncommon disorder that causes swelling of the brain and liver. The disease most commonly affects children and typically presents during recovery from a viral illness such as influenza. Common symptoms include vomiting, irritability, combativeness, confusion and seizures. Aspirin has been linked to Reye's syndrome; children with a viral illness should avoid aspirin and aspirin-containing products.
Impaired Blood Glucose Management
Diabetics are aware that an infection can wreak havoc on blood glucose management. Excessively high or low blood glucose levels are common in diabetics with the flu due to changes in activity level and food intake and the metabolic burdens of the illness. Watch your blood glucose levels carefully if you have the flu.
References
- "Principles and Practice of Infectious Diseases, Sixth Edition"; Gerald L. Mandell, M.D., John E. Bennett, M.D., Raphael Dolin, M.D., Editors; 2004
- Centers for Disease Control and Prevention: Flu symptoms and severity
- Centers for Disease Control and Prevention: Flu information for people with diabetes and caregivers of people with diabetes
- Centers for Disease Control and Prevention: Asthma, flu shots--get vaccinated
- Centers for Disease Control and Prevention: HIV/AIDS and the flu
