Influenza (flu) is an acute, highly contagious viral respiratory infection that is caused by one of three types of myxovirus influenzae. Influenza occurs all over the world and is more common during winter months. The incubation period is 24 to 48 hours. Symptoms appear approximately 72 hours after contact with the virus, and the infected person remains contagious for 3 days.
Influenza is usually a self-limited disease that lasts from 2 to 7 days. The disease also spreads rapidly through populations, creating epidemics and pandemics. Annual estimates are that approximately 20,000 deaths occur as a result of influenza virus and 250,000 to 500,000 new cases occur each year in the United States. Complications of influenza include pneumonia, myositis, exacerbation of chronic obstructive pulmonary disease (COPD), and Reye’s syndrome. In rare cases, influenza can lead to encephalitis, transverse myelitis, myocarditis, or pericarditis.
Symptoms
Initially, the flu may seem like a common cold with a runny nose, sneezing and sore throat. But colds usually develop slowly, whereas the flu tends to come on suddenly. And although a cold can be a nuisance, you usually feel much worse with the flu.
Common signs and symptoms of the flu include:
• Fever over 100.4 F (38 C)
• Aching muscles, especially in your back, arms and legs
• Chills and sweats
• Headache
• Dry, persistent cough
• Fatigue and weakness
• Nasal congestion
• Sore throat
