Testing for ebola; negative vs not positive


  • Specializes in Critical Care. Has 10 years experience.

It's important to remember when someone is tested for ebola and the result is negative, it doesn't mean they don't have ebola, it just means they haven't tested positive, which is very different from confirming someone is ebola-free. Prior to developing symptoms, a negative result isn't particularly useful.

Tests to detect ebola antibodies are more common than PCR tests, but are only useful for determining if ebola-like symptoms are in fact ebola. They are not useful in testing for whether or not someone who is still asymptomatic will eventually develop ebola symptoms and eventually have a detectable antibody level.

PCR tests can show a positive result just prior to the onset of symptoms, but will also show a negative result during the majority of the incubation period for ebola even when someone has actually contracted ebola. It's important to remember that a virus is not technically a living organism and has no real metabolism of it's own, making RNA detection unlikely until it has finished it's incubation period and entered the bloodstream.

In someone who does actually have ebola, both the antibody test and the PCR will show a negative result during the majority of the incubation period, so a "negative" result is better described as "not yet positive". Of course it also doesn't mean that the person has contracted ebola or that they are contagious while being asymptomatic.




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According to the following article, which quotes Dr. Beutner, a Nobel-prize winning physician who did his research on the immune system, and which also quotes the New England Journal of Medicine, 13% of Ebola patients exhibit no symptoms at all. Dr. Beutner thinks it's entirely possible for these asymptomatic Ebola patients to spread the disease. For this reason I support a quarantine of everyone who has had contact with an Ebola patient until the incubation period is up. http://www.nj.com/politics/index.ssf/2014/10/christies_quarantine_policy_attacked_by_aclu_cdc_and_even_the_un_is_embraced_by_2011_nobel_prize_win.html#incart_river