Bill Bryson

Making a host unwell has certain benefits for the microbe.  The symptoms of an illness often help to spread the disease.  Vomiting, sneezing and diarrhoea are excellent methods of getting out of one host and into position for boarding another.  The most effective strategy of all is to enlist the help of a mobile third party.  Infectious organisms love mosquitoes because the mosquito's sting delivers them directly into the blood stream.....

It is a mistake, however, to consider the matter too carefully from the position of logic because micro-organisms clearly are not calculating entities.  They don't care what they do to you any more than you care what distress you cause when you slaughter them by the millions with a soapy shower or a simple deodorant.

The only time your continued well-being is of consequence to a pathogen is when it kills you.... if they eliminate you before they can move on, then they may well die out themselves.