The way you would treat an infectious disease is totally dependent on the causative organism and how badly the patient is doing. 
For instance Streptococcus pneumonia is treated completely different than Clostridium defficile.
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An infectious disease can be treated in the following ways :
1.Reducing the effect of disease : in this method, the side effects or symptoms of the disease are reduced. This includes taking medicines to bring down fever or to reduce the pain,etc. However this method doesn't cure the disease.
2. Killing the cause of disease : it includes taking microbe specific medicines which will eventually kill the microbe. 
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