Most people
infected with HIV carry the virus for years before manifesting AIDS.
During that period, infected people will have few, if any, symptoms yet
they can transmit the virus.
The
percentage of women with AIDS has increased steadily, and the percentage
of people infected heterosexually has also increased, surpassing the percentage
infected through injecting drug use.
During 2001, there were 35575 newly diagnosed cases of HIV infection.
The Centers of Disease Control and Prevention (CDC) estimates
now
that 40,000 new cases of HIV transmission occur every year.
Of
the people infected with the virus of AIDS in the USA in the year 2001, 42%
were whites, 37% blacks, 20% Hispanics and <1% Asians and Pacific
Islanders and <1% American Indians and Alaska Natives.
During the 1990s, the HIV epidemic shifted steadily toward a growing
proportion of AIDS cases in blacks and Hispanics and in women.
Human Immunodeficiency Virus
(HIV) is the cause of AIDS (Acquired
ImmunoDeficiency Syndrome).
The presence of HIV in the body can be detected in several ways. The
most common is the HIV-ELISA Antibodies test.
The
HIV-ELISA
looks for the body
response to thevirus
manifested by the
presence in your blood of
Antibodies
to HIV proteins. Antibodies are special proteins that our Immune System
produce in response to the presence of HIV.
The test performed on your
sample actually consists
of two tests: a Screening test and a Confirmatory test. The
screening test procedure is called an
ELISA—Enzyme Linked Immuno-Sorbent Assay
or an EIA (Enzyme Immunosorbent Assay). The
confirmatory test is used in the event your HIV-ELISA is positive and/or
equivocal and is the procedure used is the Western
Blot Assay (WB)
The screening and
confirmatory tests are usually done using small samples of blood. If a
sample of blood tests positive repeatedly in the screening test, it will be
confirmed through the Western Blot test. People will be informed that they are infected
with HIV only after both the screening and confirmatory tests
have shown a positive (reactive) result.
Positive HIV antibody tests results
are over 99% accurate when confirmed. Negative HIV antibody tests are over
99% accurate if it has been at least six months after a contact with a
potentially HIV-infected partner. False negatives or false positives occur
rarely.
Antibodies to HIV can be
detected in the blood, in the urine or in the saliva. People produce
antibodies with different speeds and therefore the time interval between
infection and the development of antibodies to HIV can go from four weeks
to six months from the exposure date or SDC (
Suspected
Date
of
Contact).
The appearance of antibodies in a blood or urine sample of a person which
was known to be negative to HIV is called
Seroconversion.
The HIV Elisa results are usually available in one or two business days.
THE WINDOW PERIOD
The time period between a person’s
contact with the virus (infection) and when HIV antibodies become
detectable in blood or other fluids is called the "window period".
Most people will develop antibodies detectable within 4-6 weeks after infection with HIV. Some people may take
longer; but nearly all (99%) will have antibodies by 6 months following
infection. Therefore, the test may not be accurate if a person gets tested too soon after a potential exposure.
People waiting six months from the time of the exposure before testing
will have a 99% accurate test result. Until now there have been no
studies showing antibodies present in people with longer than six
months exposure to HIV.
In 1986, a second
virus causing the acquired immunodeficiency syndrome (AIDS), human
immunodeficiency virus type 2 (HIV-2), was discovered and found to be
relatively common in parts of West Africa. Because HIV-2 infections are
not always detected by HIV-1 antibody tests, antibody tests for HIV-2
have been developed. Voluntary screening for HIV-2 antibodies by blood
banks is a current acceptable practice. public health Department Clinics
now use a HIV1 and HIV2 Elisa test.
Although most HIV
infections in the United States are of HIV-1 group B subtype, current
ELISAs can accurately identify infections with nearly all non-B subtypes
and many infections with group O HIV subtypes. Infections with HIV-2 and
HIV-1 group O are rare in the United States and routine screening for
these subtypes is not generally recommended as part of diagnostic
testing except in areas where several such infections have been
identified. Routine screening for HIV-2 might be appropriate in certain
populations where potential risk for HIV-2 infection is higher (e.g., in
areas where West African immigrants have settled). Since June 1992, FDA
has recommended routine screening for antibody to HIV-2 (in addition to
HIV-1) for all blood and plasma donations. Clients with clinical,
epidemiologic, or laboratory history that suggests HIV infection and
negative or indeterminate HIV-1 screening tests should receive further
diagnostic testing to rule out HIV infection, potentially including
testing for HIV-1 non-B subtypes and HIV-2 .
Blood centers can
accomplish this either by the use of a single combination test for
HIV-1/HIV-2 or by the use of two independent tests, one for HIV-1 and
one for HIV-2. Screening donated blood and plasma for HIV-2 infection
raises issues concerning appropriate strategies for testing for both
viruses, HIV-2 testing in other settings, and notification of HIV-1 and
HIV-2 test results. What follows are CDC recommendations for the
diagnosis of HIV-1 and HIV-2 infections in persons being tested in
settings other than blood centers and CDC/FDA guidelines for serologic
testing with combination HIV-1/HIV-2 screening ELISAs.
Although HIV-2
appears to have spread in West Africa primarily via heterosexual
transmission, HIV-2 infection has been reported in Europe in homosexual
men, injecting drug users (IDUs), transfusion recipients, and men with
hemophilia. HIV-2 is endemic in parts of West Africa and has also been
reported in other parts of Africa. Apparently as a result of links with
former colonies in West Africa, Portugal and France have reported the
highest number of cases of HIV-2 infection in Europe. As of late 1989,
12.6% of AIDS cases in Portugal were caused by HIV-2. Although most of
these cases were in persons originally from Africa, HIV-2 is also
present among persons in Portugal with no known contacts with Africa.
HIV-2 infection has also been reported in India.
In the Western
hemisphere, rare cases of HIV-2 infection have been reported from
Brazil, Canada, and the United States. Within the United States, CDC and
others conduct surveillance for HIV-2, including serologic surveillance
of blood donors and populations at increased risk of HIV-1 infection.
Since 1987, 32
persons with HIV-2 infection have been reported in the United States.
Fifteen of these 32 were identified by serologic surveillance, and 17
were identified by case reports. Twenty-eight were residing in the
northeastern United States, a frequent destination for West African
immigrants and the area that has been most intensely surveyed using
HIV-2-specific tests. No cases of HIV-2 infection have been reported
among persons known to be IDUs or men reporting homosexual contact. More
than 2,700 serum specimens that were reactive by HIV-1 EIA and
indeterminate by HIV-1 Western blot have been tested for HIV-2 by either
the New York City Health Department or the Maryland Department of Health
and Mental Hygiene. HIV-2 infection was detected in specimens from 11
persons. The Massachusetts Department of Public Health identified two
HIV-2-positive specimens among blood samples from 14,779 childbearing
women. Positive HIV-2 specimens were detected among sera from two of
19,504 clients of sexually transmitted disease clinics, but in none of
the specimens from 6,547 IDUs at drug-treatment centers. In other
studies of populations at increased risk for HIV-1 infection, no cases
of HIV-2 infection have been reported. Of 15 U.S. residents found to be
positive for HIV-2 infection through serologic surveillance, demographic
information was available for seven; six were West Africans and one was
the U.S.-born wife of an HIV-2 infected West African.
