If you are exposed to certin viruses but do not contract them, can you still test positive?
All of us are exposed to bacterial and viral pathogens on a daily basis. Depending on a number of factors, we may or may not get ill and show clinical manifestations of the illness. Further, when you are exposed to pathogens, you may or may not "contract" them. Usually the bodies immunologic response prevents us from getting ill. Said another way, you may be exposed to organisms that can make you sick. Even if these pathogens do not make you ill, you can still be a carrier of the pathogen.
When you contract a virus you may or may not show laboratory test evidence of receiving that virus. A good example is influenza. When you are exposed to the flu virus you may or may not contract it and even if you contract the virus, you may or may not get sick. If you were to perform a flu swab (lab test) the test may or may not be positive. It's interesting because some people who have clinical signs and symptoms of the flu do not test positive on the test (flu swab).
Laboratory testing is a very valuable tool in diagnosing and treating disease but many times for various reasons you will have a false positive or a false negative. In other words, the test may be positive, but you may not have the disease or the test may be negative but you have all the signs and symptoms of having the disease.