Im no expert but isnt this mincing definition of pneumonia. Pneumonia is a organism that causes fluid in lungs. That organism can be many things. If the flu virus causes the lungs to fill with fluid then its the flu causing pneumonia.  But to me its a moot point. If the flu wrecks your lungs and allows a normally peaceful bacteria to get out of hand and then kill you because your lungs got their ass beat, is it the flu that killed you or that little faggot that stomped your head after the big guy knocked you out? To correct the problem do you go after the little guy or big guy? Id say the big guy (flu) but at this point were splitting hairs.