They were NOT DECIMATED! far more than 10% of them were carried off by the new diseases. Decimation is the destruction or killing of ten per cent. That is ten out of a hundred. Ninety remain. The Reds practiced decimation back in their Civil War in Russia on units that failed an objective or retreated. An offending unit was formed up, counted off, and every tenth man was shot.
Now don't get me started on "medium/media" ...