Unfortunately, the way you have worded your question makes it impossible to answer, because I don't know what you mean by "consider pneumococcal pneumonia as mandatory."  Mandatory for what?   Perhaps you could rephrase the question for us?  

of course, my question is abpout to tried to register all cases of pneumocococal CAP, so we can really known the epidemiology, resistance

I see.  The problem there, as you know, is that ascertaining the cause of pneumonia is not always straightforward.  A positive blood culture or a positive culture of a parapneumonic effusion or empyema are really the only ways to make a sure identification.  

Requiring this would obviously make sure that all cases included were truly pneumococcal but would also, generally speaking, only allow the most severe cases to be identified.  For resistance purposes this is OK but for epidemiologic purposes it would be suboptimal, unless your epidemiologic goal was simply to fully describe/understand the severe end of the pneumococcal pneumonia spectrum.  

Thanks for the clarification.

Thanks for your answer Randall