Window period is a term used to describe the period of time between the point at which a person is infected with a disease and the point at which a test can reliably detect the infection. This term is often used when discussing sexually transmitted infections, such as HIV or strains of hepatitis. During the window period, an individual is still at risk for passing on an infection despite testing negative for the condition.
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Window periods vary from infection to infection. For example, in antibody-based testing, the window period depends on the time it takes for seroconversion, when the antibody is detectable and the corresponding antigen can no longer be detected.
The window period for some diseases, such as HIV, varies depending on the testing method. Depending on the type of test administered, and the quality of the administration, this window period may be as short as 12 days (when using new tests) or as long as three months.
The window period for some conditions can also vary from person to person, depending on their genetic makeup.
The window period is important to ensure safe sex strategies. Individuals who have been tested and wish to be with new partners cannot be entirely sure they are free of sexually-transmitted diseases until that window period has passed. The window period is also integral to blood and organ donation, as individuals must not give blood or organs if there's a chance they could be contaminated.
Window periods should be used as a guide only. It’s best to use a waiting period longer than the stated window period to ensure that a person is disease-free. Abstaining from sex while a person is in a window period, or only just outside the window period, is safest. If you do want to have sex during the window period, condoms should certainly be used.