Originally Posted by birdgirl73
				
			
			Well, sometimes people who get the flu, which is caused by a virus and so can't be treated with antibiotics in the same way that a simple bacterial infection such as a sore throat or bronchitis, get "seconday" bacterial infections. That is, they're weakened and susceptible during or after the flu and so pick up bronchitis or a bacterial sore throat or sinus infection or something like that in addition to the original, primary flu. So it's simply secondary to the primary illness, which was the viral influenza. It's often hard to distinguish one disease from another, especially when you're still actively sick from the flu because that particular virus pretty well infects everything from your respiratory system to your digestive system to your joints and muscles. But once the flu has run its typical two-week course and someone is still sick, particularly still running fever of some kind, that's often an indication that a secondary infection has taken hold. (I know this because both times I've had the flu, I also ended up with secondary bronchitis.) 
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