LAUSR

HIV testing is a key component of HIV prevention. It is this critical clinical encounter that serves as the starting point for diagnosing and treating persons who are infected and delivering preventive services to those who are uninfected. Because HIV testing is so important to prevention strategies for controlling the HIV epidemic in the United States, we read with great interest the article by Hurt and colleagues in this issue, which provides an excellent overview of the current options available for HIV testing in clinical, nonclinical, and research settings. Their update highlights recent changes to nomenclature, updated data—particularly on thewindow period of HIV tests—and updates to the laboratory algorithm for diagnosis of HIV infection, at a time when this information is changing rapidly. Hurt et al. refer to changes in the “official nomenclature” of HIV tests. Although the Centers for Disease Control and Prevention (CDC) does not determine official nomenclature for HIV test types, the CDC Division of HIV/AIDS Prevention has recently made changes to Web sites and other documents that refer to the different types of HIV tests. As discussed at the 2016 HIV Diagnostics Conference, the term “generations” began to appear in the literature shortly after HIV tests that used recombinant peptides instead of viral lysate antigens (the “2nd generation”) were developed. However, the “official” nomenclature likely gained traction when Owen et al. published an article including a discussion of generations, and CDC and others largely adopted the term for use in presentations, Web pages, and other documents. Indeed, a complete description of test generations appears in both the updated Clinical & Laboratory Standards Institute standards and the CDC/Association of Public Health Laboratories (APHL) guidelines for the laboratory diagnosis of HIV infection. However, as new HIV tests continued to become available, the lines between generations began to blur. In the 2008 article, the term generation was reserved for laboratory-based, instrumented immunoassays. As Hurt et al. reviewed, single-use, point-of-care rapid tests use different technology and probably should be considered separately. Nevertheless, both test manufacturers and authors evaluating these tests began to use the term generations to describe rapid tests. Originally, the generations described incremental improvements in test sensitivity and specificity. However, some of the newer tests within the same generation have different sensitivity for early infection. These differences can largely be explained by other aspects of test design, for example, whether they are lateral flow or immunconcentrating rapid tests, reagents used for detection of analytes, or the volume of sample required to perform the test. In addition, there are also IgGsensitive rapid tests that differentiate HIV-1 from HIV-2, and new tests that differentiate p24antigen detection from antibody detection, but have the same sensitivity during early infection as tests that report only one signal as “reactive for p24-antigen and/or HIV antibody.” As a result, in the article documenting seroconversion sensitivity on plasma specimens that Hurt et al. referenced, tests were described in terms of the analytes they can detect and the types of technology (instrumented, laboratory-based, vs. single-use, rapid) that they use to do so. These changes have been implemented in CDCWeb pages and documents contained therein. In particular, the advantages/disadvantages of Food and Drug Administration–approved HIV tests guide may be particularly useful for clinicians and others who need to understand differences in characteristics of the tests available in the United States. In addition to changing the way we refer to types of HIV tests, CDC has also updated messaging about test window periods. On the basis of new data highlighted by Hurt and colleagues, information related to retesting after an exposure, when the initial test result is negative, but within the “window period” for the test being performed has been revised. These changes include defining the window period as the time between when a personmay have been exposed to HIVand when a test can tell for sure if they have HIVor not, and defining that time as 45 days for laboratory-based antigen/antibody tests performed on plasma or serum specimens. This is much shorter than the previously recommended 90 days that