June 27 is National HIV Testing Day. The CDC has put together several resources for the Sermo community about HIV diagnosis and new screening recommendations. Read more about how CDC HIV Screening Standard Care is helping physicians meet the challenge of identifying persons with HIV through HIV testing e-Inquiry Service. Below is a case study from Philip J. Peters, MD, DTM&H.
If you’re an M.D. or D.O. you can read more from the CDC inside Sermo.
Brief Case Report: A 39-year-old man reports to an emergency department with complaints of fever and abdominal pain. On social history, he reports being married and that his wife has been his only sex partner in the past 10 years. He denies injection drug use. An HIV test is sent with his initial lab panel. A preliminary lab report returned the same day indicates that the Architect HIV Ag/Ab Combo assay was repeated reactive and that the Western blot test result is pending. The Western blot result is reported as negative (no bands) 2 days later.
Question: Persons with a reactive fourth-generation HIV immunoassay test and a negative HIV supplemental test (e.g., Western blot test) should
- be reassured that they are HIV negative
- be offered HIV antiretroviral medications for post-exposure prophylaxis
- be referred to an HIV care provider
- receive HIV-1 RNA testing or follow-up HIV testing in 2 to 4 weeks
Follow-up: An HIV-1 viral load is reported as greater than 10 million copies/mL. The patient has an upper endoscopy this is consistent with esophageal candidiasis, which is treated with fluconazole. The patient is enrolled in HIV outpatient care.
Diagnosing Acute HIV Infection
The highly infectious phase of acute HIV infection—the interval between the appearance of HIV RNA in plasma and the detection of HIV-1-specific antibodies—contributes disproportionately to HIV transmission. Diagnosing acute HIV infection during this interval is critical because individuals are highly infectious (i.e., the HIV viral load often exceeds one million copies/mL), they have de facto recently engaged in high-risk behaviors, and they are unaware that they are infected with HIV.
Because first- and second-generation HIV immunoassay tests were only able to detect immunoglobulin G (IgG)-class antibodies against HIV, they could not be used to diagnose acute HIV infection. In 2011, fourth-generation immunoassay tests were approved by the FDA. These immunoassays can detect both early IgG-class and immunoglobulin M (IgM)-class antibodies as well as the HIV p24 antigen, a major core protein of HIV. The HIV p24 antigen can be detected early, before antibody appears, allowing the fourth-generation HIV tests to identify some HIV infections in the acute phase.
Laboratories are increasingly using fourth-generation HIV tests. However, the assay’s greater sensitivity for acute HIV infection can be diagnostically problematic. The HIV diagnostic algorithm first proposed in 1989 recommends performing two tests in sequence to diagnose HIV infection. The initial screening test is the HIV immunoassay. If this test is reactive, a supplemental test is performed, such as the Western blot. Although there have been advances in screening immunoassays, the Western blot remains unable to detect IgM-class antibody and the HIV p24 antigen.
A New HIV Diagnostic Algorithm
Because the fourth-generation immunoassay tests detect HIV infection earlier than the Western blot test, reactive fourth-generation HIV test results and negative Western blot results early in the course of HIV infection can be interpreted erroneously as negative for HIV infection. False-negative test results may lead to adverse clinical outcomes for patients and to further HIV transmission in the community. To address this problem, CDC is evaluating a new HIV diagnostic algorithm.
The new algorithm includes an RNA test as an additional test, if needed, to resolve reactive fourth-generation immunoassay test results with negative supplemental test results (Figure 1). In a prospective study that evaluated this new algorithm, of the 99 high-risk individuals (predominately men who have sex with men) with a reactive fourth-generation HIV immunoassay test and a negative supplemental test, HIV-1 RNA testing determined that nearly 56% had acute HIV infection; the other 44% were HIV negative.
Improved Diagnosis of Acute HIV Infection
Improved HIV immunoassay tests are an important clinical advance because they have enhanced the ability to detect HIV infection earlier, even during the acute phase of infection when substantial HIV transmission occurs. Specimens with reactive HIV immunoassay test results and negative supplemental test results, however, must undergo additional testing to differentiate acute HIV infection from false-positive results.
As the use of fourth-generation HIV immunoassay tests become more widespread, automatic reflex testing with an HIV-1 RNA test may become more common. In the interim, clinicians can remain vigilant for these discordant test results and either order an HIV RNA test or obtain follow-up HIV testing (in 2 to 4 weeks) to more accurately determine whether HIV infection is present.
Figure 1. New HIV diagnostic testing algorithm evaluated — United States, 2011–2013
Source: Centers for Disease Control and Prevention. MMWR. 2013;62(24):489-494.
Abbreviation: HIV = human immunodeficiency virus.
* Additional testing required to rule out dual infection with HIV-1 and HIV-2.
Alternate Text: The figure above is a flowchart depicting the new human immunodeficiency virus (HIV) diagnostic algorithm, which replaces the Western blot test with an HIV-1/HIV-2 antibody differentiation assay as the supplemental test and includes an RNA test to resolve a reactive immunoassay with a negative supplemental test result.
HIV Screening. Standard Care. TM
The HIV Screening. Standard Care. program, part of CDC’s Act Against AIDS communication campaign, provides free tools and resources for incorporating HIV testing into primary care settings. CDC recommends testing for all patients ages 13-64. The campaign can be found online: http://1.usa.gov/1iddFh7
To learn more about CDC’s HIV screening recommendations in health care settings and the new HIV diagnostic testing algorithm:
- Centers for Disease Control and Prevention, Act Against AIDS. HIV Screening. Standard Care.TM 2014.
- Centers for Disease Control and Prevention. Detection of acute HIV infection in two evaluations of a new HIV diagnostic testing algorithm – United States, 2011–2013. MMWR. 2013;62(24):489-494.
- Pandori MW, Westheimer E, Gay C, et al. The Multispot Rapid HIV-1/HIV-2 differentiation assay is comparable with the Western blot and an immunofluorescence assay at confirming HIV infection in a prospective study in three regions of the United States. J Clin Virol. 2013;58(Suppl 1):e92–96.
Philip J. Peters, MD, DTM&H, is a Medical Officer with the Division of HIV/AIDS Prevention, US Centers for Disease Control and Prevention, in Atlanta, Georgia. Dr. Peters is the activity leader for HIV testing in the Division of HIV/AIDS Prevention’s Epidemiology Branch. He is responsible for conducting epidemiologic and biomedical research activities to evaluate acute HIV infection and his professional interests include improving HIV diagnosis in the clinical setting.
Disclosure: Philip J. Peters, MD, DTM&H, has disclosed no relevant financial relationships.