Dear Sir,

I was wondering if you could answer a few questions for me. I have been perusing several websites on HIV/AIDS, and I have been talking to many people about HIV antibody testing. Some people say 3 months is the length of the window period. Some people say 6 months is the length of the window period. The experts' views on this website have all suggested that at 3 months post exposure, an HIV antibody test is greater than 99 accurate. I have noticed that you yourself posted a Q&A ("Testing?") stating that no one who tested negative on ELISA at 3 months tested positive at 4 to 6 months. So if there is so much consensus that after 3 months an HIV antibody test is good as gold, why would the workers at the local department of health tell me that the HIV antibody test is good only after 6 months post exposure? Why have I read in a couple of places a detectable presence of HIV antibodies may take up to 6 months to develop? Am I just getting confused by people who have incomplete or old data? I have chosen to believe experts like yourself, but I am still wondering why there seems to be so much difference of opinion as to the length of something as free of opinion as the window period.

Thank you.

Because there is opinion, expert opinion and there is objective peered reviewed data. Official agencies (like the CDC), use a combination of information to formulate guidelines. Their guidelines will always be the most conservative.