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False Negatives (ELISA) and HIV-2
Apr 1, 1997
Doctor, Thank you for providing an invaluable and highly appreciated
service. I have two questions: 1. The ELISA test can return a 'false
negative' if the test is done too soon. The second time is after the
body no longer is producing the antibodies the test looks for. How long
after seroconversion does this second phase usually take? Would symptoms
be in place before that time? 2. What is the difference (other than
geographic) between HIV-1 and HIV-2 (time to seroconversion, symptoms)?
Thanks again for a great service!
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Response from Mr. Sowadsky
Hi. Thank you for your question.
When a person is infected with HIV, it can
take up to 6 months to show positive on the test (Average = 25 days, usual
time = 3 months, maximum time at 99% accuracy = 6 months). If a person gets
tested prior to 6 months, the antibody tests may not detect the infection (a
false negative). At 6 months and beyond, the ELISA/Western Blot tests will
normally show positive for the rest of the persons life. In some cases, at
the very terminal stages of AIDS, the immune system could be so damaged, that
the antibody tests could revert back to a negative result. But I must
emphasize that this would occur at the very terminal stages of AIDS.
As far as HIV-2 is concerned, this virus is only rarely found outside of
Western Africa. This is a separate virus from HIV-1 (not a strain of HIV-1).
Both HIV-1 and HIV-2 cause the same disease, and are transmitted the same
way. The only people who would be at risk for HIV-2 would be West Africans,
and sex/needle sharing partners of West Africans. In the United States, as
of June 30, 1995, there were only 62 reported cases of HIV-2 infection. This
compares to the estimated 650,000-900,000 cases of HIV-1 in the USA. The
vast majority of these 62 cases were in West Africans, or persons having sex
or sharing needles with West Africans.
The only routine testing for HIV-2 is
in the blood supply. However, DO NOT DONATE BLOOD TO BE TESTED FOR HIV-2! If
you have been at risk for HIV-2 (as described above), discuss this with your
physician, who can then order an HIV-2 test, if it's necessary. Because
HIV-2 is so rare outside of Western Africa, most testing clinics do not do
HIV-2 testing. Home tests are also limited to HIV-1 testing only. But a
physician can specially order the test if the need is there. However, if
you didn't have a West African connection, you would not be considered at
risk for HIV-2. The 6 month window period for HIV-1 testing should apply for
HIV-2 as well.
The studies I have seen state the amount of virus found in the body is
generally lower for HIV-2, as compared to HIV-1. One can generally assume
that HIV-2 may be less infectious than HIV-1. In addition, this lower amount
of HIV-2 in the body may account for the longer period of time it takes for
HIV-2 to lead to full-blown AIDS, as compared to HIV-1. HIV-1 takes an
average of 10 years before it leads to full-blown AIDS. HIV-2 generally
takes longer than 10 years to become full-blown AIDS.
If you have any further questions, please feel free to call the Centers for Disease Control at 1.800.232.4636 (Nationwide).
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