Respiratory infection caused the most deaths in 1999.
- The proportion of respiratory samples that tested positive for influenza peaked during the 1999–2000 flu season at 33%, while the state and territorial epidemiologists' reports peaked at 44 states reporting either regional or widespread influenza activity.
- It was originally discovered in military soldiers in the US in the spring of 1918.
- One third of the world's population, or roughly 500 million people, are thought to have contracted this virus.
- The lungs, nose, and throat are affected by the flu. High-risk groups include young children, elderly individuals, pregnant women, persons with chronic illnesses, and those with weakened immune systems.
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