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Window Period!
      #26703 - 01/09/02 07:59 AM

I hope the following information provides the information you seek. The
information is excerpted from a joint paper produced by the state and
NYCity Depts of Health.

Update on the Window Period for HIV Infection
New York State and New York City Joint Recommendations For HIV Testing and

What is the Window Period?

The window period is the length of time after infection that it takes for a
person to develop enough specific antibodies to be detected by our current
testing methods. If an individual engages in unsafe sex or shares drug
injection equipment and becomes infected, the body will make antibodies to
fight HIV. When enough antibodies are developed, the HIV antibody test
will come back positive. Each person=s body responds to HIV infection a
little differently, so the window period varies slightly from person to
person. HIV is most commonly diagnosed in adolescents and adults through
HIV antibody testing. However, there are also tests that diagnose HIV
infection by detecting certain parts of the genetic material of HIV. PCR
(polymerase chain reaction) tests are used to diagnose HIV infection in
infants. Viral culture may also be performed in certain circumstances to
diagnose HIV.

How Has Our Understanding of the Window Period Changed Over the Years?

Early in the epidemic, our testing methods were not as sensitive as they
are today. Doctors and public health officials wanted to make sure that
people who engaged in risk behaviors for HIV were tested long enough after
their risk to be sure that anyone who was actually infected would test
positive. The Centers for Disease Control currently states that people
with possible exposure to HIV, who test negative, should be re-tested six
months after the possible exposure to ensure that sufficient time has
elapsed to make antibodies. However, as early as 1990, the Association of
State and Territorial Public Health Laboratory Directors reached a
consensus recommendation that virtually all seroconversions are complete
within twelve weeks of exposure. Improvements in HIV testing technology
over the last fifteen years, increasing laboratory experience with testing
and the ability to better monitor early infection through PCR testing have
contributed greatly to our understanding of the window period and have
provided increased confidence that virtually all cases of HIV infection can
be detected by three months.

What is the best time for the first HIV test after a possible exposure to

Most people infected with HIV will develop enough antibodies to be detected
by our current HIV antibody tests four weeks after the exposure. This
means that, for example, if a person had unsafe sex and became infected on
January 1, it is likely that he/she will have enough antibodies to test
positive four weeks later. If the person tests positive, this early testing
is beneficial because the person can begin receiving medical care very
early in the course of the infection. Recent advances in care and
treatment for HIV infection have increased the advantages of early
identification and treatment. Therefore, especially when HIV infection is
highly suspected, the first HIV test take place four weeks after the
exposure. In cases of occupational exposure or exposure through sexual
assault, an HIV test is also recommended immediately after the exposure to
establish baseline HIV status. The protocol for testing following
occupational exposure remains unchanged by this new policy with tests
recommended at baseline, six weeks, three months and six months
post-exposure. (See MMWR 1996;45(22):468-472)

How long after a possible exposure to HIV does the person have to wait to
be tested to be sure he/she is not infected?

It is possible that someone who tests negative four weeks after an exposure
may be infected but his/her body has not had sufficient time to develop
antibodies. Therefore, to rule out HIV infection, it is important to
re-test three months after the exposure. It is extremely rare for an
HIV-infected individual to not develop antibodies by three months. An
individual who tests negative three months after an exposure does not
require further testing unless he/she may have repeated exposures or if
their antibody test results are incompatible with their clinical history.

What is the recommendation for testing for individuals who engage in
on-going risk behavior?

The primary focus of our work with individuals who place themselves at
on-going risk for HIV infection must be continued education, behavioral
counseling and harm reduction, such as education about safer injection
practices and referral to syringe exchange programs and drug rehabilitation
services. HIV testing offers no Aprotection@ from HIV infection. When an
individual is engaging in ongoing risk behavior it is not possible to
develop a timeline for re-testing based on a single exposure. An
individual with a negative HIV test who engages in on-going risk behavior
should be offered testing every three months and counseled to avoid risk
behavior. In these cases, the function of testing is to ensure early
access to care in the event that the individual becomes HIV positive.

For more information about the window period, consult the following

Bartlet JG. Serology and Baseline Laboratory Studies for Human
Immunodeficiency Virus Infection Infectious Diseases in Clinical Practice,
Vol. 4, No. 5, pp 334-42.

Busch MP, Lee LL, et al. Time Course of Detection of Viral and Serologic
Markers Preceding Human Immunodeficiency Virus Type 1 Seroconversion:
Implications for Screening of Blood and Tissue Donors. Transfusion, 1995
Vol. 35, No. 2, pp 91-7.

Lackritz EM, Satten GA, et al. Estimated Risk of the Human Immunodeficiency
Virus by Screened Blood in the United States New England Journal of
Medicine, Vol.333, Number 26, pp 1721-25.

Report and Recommendations: Fifth Consensus Conference on Testing for Human
Retroviruses, March 6-8, 1990; Association of State and Territorial Public
Health Laboratory Directors

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