What two things are necessary to prove an exposure occurred

When assessing a possible exposure, it is necessary to note both the portal of entry and the mode of transmission. In simple terms, exposure to communicable disease requires two components. First component is a method of transmission wherein a pathogen enters the body. For example, a needle stick incident, the needle is the method of travel. The infected material travels from the host patient to the employee by way of the needle. The second component is the portal of entry. It is the path through which the infected material gains entry into the body. Referring to our example earlier, in the needle stick incident, the place where the needle punctures the skin is the portal of entry for the disease.

More than 600. i'm just guessing