The influenza virus causes a respiratory infection with symptoms similar to the common cold, but also often causes more severe symptoms, such as high fever, muscle aches, and weakness.
Symptoms may begin abruptly within one to four days of acquiring the infection. However, an infected person can pass the virus to others before symptoms begin and for approximately one week after the start of symptoms. In most cases, the disease resolves on its own. In high-risk populations, however, influenza can be life-threatening.
Influenza has become a matter of increasing concern due to the recent outbreaks of H5N1 avian influenza ("bird flu"). Birds can carry influenza viruses in their digestive tracts and may transmit the viruses to humans.
- Contact with infected individuals: Direct contact with persons who have an upper respiratory infection permits transmission of the virus. Coughing or sneezing can spread the virus through the air.
- Closed settings: Homes and schools have higher transmission rates, compared with typical work settings.
- Immunocompromise: Persons with compromised immune systems, including those with malnutrition, diabetes, and chronic lung disease, generally have a more severe disease if they are infected by influenza.
- Winter season: Influenza infections more commonly occur in the winter, but cold climates are not necessarily a risk factor for the disease.
- Contact with infected birds: Risk for H5N1 influenza is principally related to contact with infected birds, bird feces, or bird products.
Influenza: Diagnosis and Treatment
- A medical history and physical examination are the first steps. Influenza typically has few physical symptoms and, in mild cases, may be indistinguishable from common colds. Individuals with symptoms of lung infection, such as shortness of breath, should be evaluated for pneumonia. Persons who appear seriously ill may require hospitalization and antibiotic treatment when bacterial pneumonia or severe infection is suspected.
- Rapid influenza tests that identify the influenza virus are often used for diagnosis.
- If pneumonia or other lung diseases are suspected, chest X-ray, blood tests, and cultures may be recommended.
- Preventive measures to avoid infection include covering the mouth and nose when coughing and sneezing, washing hands appropriately, and avoiding touching one's eyes and nose.
- Vaccines do not always prevent influenza and will not protect against new strains of avian influenza. However, annual vaccines theoretically help prevent epidemics by reducing the possibility that individuals can be simultaneously infected with a typical seasonal influenza virus and avian influenza, a scenario that can lead to the development of new viral strains. Exercise (more than 20 minutes, three times per week) appears to improve vaccine response, particularly in the elderly. In addition, some evidence suggests that stress-management interventions can produce better response to the flu vaccination.
- Antivirals, if started within 48 hours of the onset of symptoms, may decrease the length of illness. The following antivirals may reduce symptoms and shorten the course of disease: Amantadine, rimantadine, oseltamivir (Tamiflu), zanamivir (Relenza), and probenicid.
- Acetaminophen (Tylenol), aspirin, and ibuprofen may improve symptoms, particularly fever and muscle aches. However, aspirin should never be used in children with viral infections due to the risk of Reye's syndrome, a deadly disease that primarily affects the brain and liver.
Influenza: Nutritional Considerations
Few research studies have investigated nutritional factors in the risk of developing influenza or its severity after infection. However, black elder, a botanical extract, contains high levels of naturally occurring flavonoids that have been shown to act against influenza and other viruses. Two well-designed clinical trials found that black elderberry extract reduced the duration of influenza by more than 50 percent. Further research is necessary to confirm its effectiveness.