But even the most sensitive tests will fail to detect the early stages of the virus and some people who are infected can keep testing negative for a few days. No test detects the virus immediately after the person becomes infected. The more rigorous PCR test  also manufactured by big companies such as Abbott Labs  takes about 612 hours to analyze in machines that can handle a couple thousand samples at a time. There is no such thing as a 100 percent perfect and instantaneous test  for any disease.AdvertisementSome academic institutions have said that Abbotts ID Now test misses infections 20 to 30 percent of the time. "We know that false negatives do occur, especially early in the course of infection.
At least 20 percent passed by ulterior testing.
( z0 pass :ARG1 ( z1 at-least :op ( z2 percentage-entity :value 20 ) ) :ARG2 ( z3 test :mod ( z4 ulterior ) ) )
(z0 / pass-07
    :ARG1 (z1 / at-least
              :op1 (z2 / percentage-entity
                       :value 20))
    :ARG2 (z3 / test-01
              :mod (z4 / ulterior)))
At least 20 percent passed by ulterior testing .
z2 :value 0
z1 :op1 z2
z0 :ARG1 z1
z3 :mod z4
z0 :ARG2 z3