Home HealthTopics Health Centers Reference Library Research
Join us on Facebook Join us on Facebook Share on Facebook


What Is The Window Period For HIV And What Is MEIA?



Thanks a lot for a great job you are doing here. I had protected vaginal intercourse (condom didn`t break nor slip) with an unknown HIV status woman. HIV counseler said there is no risk, even though, I got tested at 12 and 13 weeks, both came back negative, reports said: MEIA NonReactive.

What is MEIA? Is it accurate? I am so confused about window period, is it 12 weeks or 24 weeks? Do I have to get tested at 24 weeks? An HIV counselor in Toronto said that I don`t need any further testing and he said the window period is 12 weeks according to CDC, but I've read so many different answers over the internet Who should I trust? Please help.


You have several questions, which I will attempt to answer in a stepwise fashion. Let us start with the nature of your potential exposure to HIV. You had vaginal protected intercourse with a person of unknown HIV status, with no obvious breakage in the barrier. I assume that no other exchange of bodily fluids took place. Under the described circumstances, the probability of acquiring HIV infection is very low, albeit non-zero. Let me elaborate: a constellation of unlikely eventualities would have to happen:

 1) the Prevalence of HIV in North America general population is below 1%. You did not provide more information about your contact, but the prevalence of HIV among certain populations: sex workers, injection drug users, certain geographic areas is higher, but no more that 20%.

2) The female to male transmission of HIV is less efficient than male to male and male to female.

3) The use of barrier methods further decreases the probability of HIV transmission, but is not 100% effective. Failure to protect is associated with breakage, slippage and undetectable porosity in the condom.

You are still concerned and opted to obtain HIV testing. MEIA stands for Microplate Enzymatic Immunoassay. This is a synonym for ELISA, which is a better known name for the test. MEIA measures the presence of antibodies against HIV proteins, which are produced by the immune system in response to HIV infection. The test becomes positive at a variable number of weeks after the initial infection. The majority (90%) of individuals sero-convert, after 12 weeks of exposure, and >99% after 24 weeks. That is why you see recommendations for testing at 12 and 24 weeks, to account for the remote chance of a "late" seroconversion.

If you want to further assure yourself you did not acquire HIV, you should get a 24 week test. Testing anytime sooner will not provide any more information. It is also important to address the anxiety and fear around HIV infection and disease. Post-testing counseling, a candid interview with your doctor or a knowledgeable person that you trust, debunking of the myths and realities about HIV could be much more helpful than any blood test.

For more information:

Go to the HIV and AIDS health topic, where you can:

Response by:

Francisco   Gomez, MD Francisco Gomez, MD
Assistant Professor
College of Medicine
University of Cincinnati