Posted September 2009 — Currently Under Revision

Update on the Window Period for HIV Infection

New York State Recommendations for HIV Testing and Re-testing

1. What is the Window Period?

HIV is most commonly diagnosed in adolescents and adults through HIV antibody testing. The window period is the length of time after infection that it takes for a person to develop enough antibodies to HIV to be detected by current blood or oral fluid HIV antibody tests. When an individual becomes infected, his or her body will develop antibodies against HIV. Once enough antibodies are developed, the HIV antibody test result will be positive. Most people who become infected with HIV will develop enough antibodies to be detected by current HIV antibody tests 3-6 weeks after the exposure. Each person’s body responds to HIV infection a little differently, so the window period varies slightly from person to person. It is unusual for an HIV-infected individual to not develop antibodies by 3 months after the suspected exposure. A person who tests HIV antibody negative 3 months after an exposure does not require further testing unless he/she has had repeated exposures or if the antibody test results are incompatible with the person’s clinical history.

2. What is acute HIV infection and can it be detected by HIV antibody tests?

Acute HIV infection is the very early, initial stage of HIV infection when the virus is multiplying rapidly and the body has not yet developed antibodies to fight HIV infection. Symptoms of acute HIV infection, if they are present, might include fever, fatigue or malaise, joint pain, headache, loss of appetite, rash, night sweats, myalgias, nausea or diarrhea, and/or pharyngitis. HIV antibody tests will not generally detect HIV infection during this early acute stage of infection. However, there are other tests that diagnose HIV infection by detecting certain parts of the genetic material of HIV. RNA PCR tests (polymerase chain reaction) detect the RNA genetic material of HIV and can be used to diagnose acute HIV infection. These tests should be used when the clinical suspicion is high for acute HIV infection, the standard antibody tests are negative, and the confirmatory Western blot tests are either negative or indeterminate.

3. What is the suggested testing protocol for a person who reports a likely recent exposure to HIV?

For patients who do not present with symptoms of acute retroviral syndrome, HIV antibody testing should be offered at that time. A negative antibody test should be followed up with repeat testing at 3 to 6 weeks. In most cases, HIV antibody testing performed 3 to 6 weeks after the possible exposure will detect HIV infection if it is present. In a small number of cases, someone who tests HIV antibody negative 6 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 perform the HIV antibody test 3 months after the exposure. It is extremely rare for an HIV-infected individual to not develop antibodies by 3 months. Individuals who test negative 3 months after an exposure do not require further testing unless they have had repeated exposures or their antibody test results are incompatible with their clinical history.

For patients who report a possible exposure to HIV and who develop symptoms suggestive of acute HIV infection (e.g., fever, fatigue or malaise, joint pain, headache, loss of appetite, rash, night sweats, myalgias, nausea or diarrhea, pharyngitis), medical evaluation should occur immediately. A plasma HIV RNA assay should be used in conjunction with an HIV-1 antibody test to diagnose acute HIV infection.

4. What is the post-exposure protocol for persons who report an exposure within 36 hours?

There is now guidance available for management of exposures if they are reported immediately. If a patient reports a possible exposure to HIV within 36 hours of the exposure, the patient should be immediately evaluated for post-exposure prophylaxis (PEP). When PEP is initiated immediately after an exposure, it can prevent HIV infection. PEP should be prescribed for patients who present within 36 hours of an HIV exposure; ideally, it should be initiated within 2 hours of the exposure. See HIV Prophylaxis Following Occupational Exposure and HIV Prophylaxis Following Non-Occupational Exposure Including Sexual Assault.

The protocol for testing following occupational exposure recommends testing at baseline, 1 month, 3 months, and 6 months post-exposure. See HIV Prophylaxis Following Occupational Exposure.

5. What are guidelines for routine HIV testing of all adults regardless of risk exposures?

The New York State Department of Health and the Centers for Disease Control and Prevention recommend offering HIV testing to all adults, not just those who engage in risk behaviors, as a routine part of health care.

6. What is the recommendation for testing individuals who engage in ongoing risk behavior?

The primary focus for individuals who place themselves at ongoing risk for HIV infection is continued education, behavioral counseling, and harm reduction. Risk-reduction counseling should include education about safer sexual practices, condom use, safer injection practices, referral to syringe exchange programs, and drug rehabilitation services. HIV testing offers no “protection” 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 ongoing risk behavior should be offered testing every 3 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 and to prevent transmission of HIV to others.

For more information about HIV testing and the window period, consult the following articles:

Branson BM, Handsfield HH, Lampe MA, et al. Revised Recommendations for HIV Testing of Adults, Adolescents, and Pregnant Women in Health-Care Settings CDC Testing 2006. Morb Mortal Wkly Rep MMWR 2006;55(RR-14):1-17. Available at: http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5514a1.htm

Medical Care Criteria Committee. Diagnostic, Monitoring, and Resistance Laboratory Tests for HIV. New York State Department of Health AIDS Institute. February 2011. Available at: www.hivguidelines.org.

Dodd RY, Notari EP, Stramer SL. Current prevalence and incidence of infectious disease markers and estimated window-period risk in the American Red Cross blood donor population. Transfusion 2002;42:975-979. [PubMed]

Patel P, Klausner JD, Bacon OM, et al. Detection of acute HIV infections in high-risk patients in California. J Acquir Immune Defic Syndr 2006;42:75-79. [PubMed]

Stekler J, Maenza J, Stevens CE, et al. Screening for acute HIV infection: Lessons learned. Clin Infect Dis 2007;44:459-461. [PubMed]

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