When someone is coming to a clinic for a routine HIV test, we usually recommend testing at 6 weeks and 3 months. This is done because 95% of tests are accurate after 6 weeks, but it can take up to 3 months for a final result.
In your case testing is treated differently because it was an occupational exposure. This means that you come under the blood and body fluid exposure management guidelines of your employer.
The testing recommended in the blood and body fluid exposure manual is meant to cover all types of situations, and because several things are being tested at the same times.
For example, HIV testing is recommended at 9 months because the HIV window period can be affected if the person took post exposure prophylaxis (PEP) to try and prevent an HIV infection. Click here for more information about PEP.
Because this is work related, I recommend that you talk with your occupational health department about your situation, and why they recommend follow up testing at 6 and 9 months.
Here is a link to the blood and body fluid exposure management guidelines posted on the BC Center for Disease Control website.
Please leave a comment to let us know if this answers your question or if you need more info.