From the San Francisco AIDS Foundation:
What's the specific window period for different types of HIV tests?
Antibody tests ("Rapid" tests) ? give a positive result based on antibodies to HIV, not the virus itself.
2-8 weeks (up to 2 months) after infection, most people will have enough antibodies to test positive
12 weeks (3 months) after infection, about 97% of people will have enough antibodies to test positive
Antigen tests (RNA tests) ? show a positive result based on the presence of the virus. These tests are more expensive than anitbody tests, so are not offered in as many places.
1-3 weeks after infection, there will be enough viral material for a positive result
Regardless they should quarantine the first & possibly second generation exposures for the full 12 weeks.
