Many are clearly related to a head injury or a viral illness.

"Someone comes to me with a viral illness, there is a battery of tests we can run," he said.

Sometimes it is difficult to tell whether you have influenza or some other viral illness.

Isolation is most commonly used when a patient has a viral illness.

Even a healthy pregnant woman could get a viral illness, he reasoned.

She pulled out before the tournament began with a viral illness.

Symptoms usually develop 3 to 7 days after the viral illness starts.

Maybe a few kids had a viral illness of some sort, but with most, it was sympathetic.

You become suddenly quite weak following a typical viral illness.

Did it start following a typical viral illness, such as a cold?