A blood test for virus does not look for actual virus particles, but actually the antibodies produced in response to infection. So it’s possible to have the virus and not yet have a detectable immune response.
I have wondered if the most recent strain of Ebola had been studied in a sufficiently controlled environment to support the absolutes being offered by Prince Obie’s administration...
Thanks for pointing that out.
It takes one or two weeks for the body to start producing antibodies. While looking for antibodies is a good way to find evidence of past infection, it won't pick up an infection early in the process.
Blood is tested for Ebola by doing a PCR assay, which detects virus RNA. When a person first becomes symptomatic, the PCR test is often negative, but it will be positive a day or so later. Whether this means there is no virus in the blood at that time, or the amount is too low to be detected is an unknown.
Many infections that are diagnosed by PCR of the blood behave the same way--not detectable right away, but are detectable a day or a few days later.