unless someone has a SEVERELY compromised immune system, there is no reason to test beyond 3 months post exposure.
now, frequently catching colds, etc does NOT constitute a severely compromised immune system. this comes from things such as chemotherapy, taking anti-rejection drugs following an organ transplant, and being an CHRONIC, LONGTERM iv drug user.
3 months post exposure for a conclusive result is the CURRENT guideline.
it's been 3 months since 2004