Pasteurising temperature and holding time will vary according to the purpose of the final product, e.g. if you want to make cheese, yoghurt, ice cream, it will not be Pasteurised at the same temperature.
The pasteurising unit needs input from various services e.g. steam, water, ice water, compressed air, electricity.
Re-contamination of milk can occur directly. I.e. that the infectious agent is transmitted directly from a sick person to the milk.
Likewise, a disease can be transmitted indirectly. Here the disease is first transmitted to the cow and the milk will contain many bacteria, streptococci, which in humans can cause angina and scarlet fever.
Persons suffering from diseases must be removed immediately from the work of milk extraction, treatment, and distribution
Note: Government regulation for temperature treatment can vary from Country to Country or even from community to community.