Harvard Health Letter

In Brief: How do you know whether it's flu?

On the misery index, flu ordinarily outdoes the common cold. The fatigue, fever, headaches, and muscle aches — they're much worse than the stuffed-up head and nose of the common cold. And the H1N1 virus may add vomiting and diarrhea to the usual flu woes.

Still, especially at the beginning stages, it can be hard to tell whether it's flu or "just a cold." Doctors can test for the presence of a flu virus but usually do so only if patients are grievously ill and may need to be admitted to the hospital, if they haven't been already. Quick recognition is important because antiviral drugs are most effective during the first couple of days of symptoms. And this year especially, you'll want to stay home if flu is a possibility. So here's a quick side-by-side comparison of flu and cold symptoms to help you figure out what's ailing you:

Symptom

Flu

Cold

Fever

A classic flu symptom. Often comes on suddenly and may last for days.

Rarely occurs.

Cough and sore throat

Also classic symptoms. The cough is dry and hacking.

Can be a problem but is usually not that bad.

Stuffy nose

Sometimes.

The defining symptom.

Fatigue

Often hard to shake and may linger for weeks.

Moderate, although impaired breathing can lead to bad sleep.

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