Answer:
C. After they become infected even if they look and feel healthy.
Step-by-step explanation:
HIV is a virus and even when you don't have symptoms, if you have it, you can still infect others. Not taking an HIV test doesn't mean you don't have it, it just means that you don't know that you have it. And I don't think an opportunistic infection would really change the affect of a virus spreading.
A virus can spread no matter the circumstances, it doesn't care what type of person you are or what background you have; and it's kind of like cancer in that way.