Able to simultaneously detect HIV antibody and HIV-1 p24 antigen, fourth generation HIV screening assays are the latest advances in HIV serological testing. Developed to detect both acute and latent infections in a time- and cost-efficient way, most of such fourth generation diagnostic assays (e.g. ELISAs) are laboratory-based and are therefore not appropriate for point-of-care (POC) application or for use in challenging environments such as in less developed countries. Now, the newly developed immunochromatographic rapid test, the Determine HIV-1/2 Ag/Ab Combo test from Inverness Medical means that the benefits of fourth-generation HIV screening can be achieved virtually anywhere, including in POC situations.
by Dr T. Guidasci
Despite decades of aggressive prevention efforts and significant advances in effective treatment, HIV infection and AIDS (Acquired Immune Deficiency Syndrome) remain a worldwide pandemic, with serious socio-economic consequences [1, 2]. HIV affects 33.2 million people worldwide, 2.1 million of whom live in Western and Central Europe and N. America [1]. According to the latest data from The Joint United Nations Programme on HIV/AIDS (UNAIDS), 2.5 million people were newly infected with HIV in 2007 [1]. UNAIDS and the World Health Organisation (WHO) estimate that every day, over 6800 people become infected with HIV and over 5700 people die from AIDS, due to inadequate access to HIV prevention and treatment services [1].
The epidemic proportions of HIV and AIDS are particularly evident in the developing world. Sub-Saharan Africa accounts for 67% of all people living with HIV and for 72% of AIDS-related deaths in 2007 [3]. In addition to the huge medical and social impact of HIV/AIDS in these areas, there is also significant overall economic impact. The situation is made worse by the low availability of antiretroviral treatment and services for patients, including children orphaned or made vulnerable by HIV. Approximately 12 million children under the age of 18 have lost one or both parents due to AIDS in sub-Saharan Africa, and this number is expected to continue to rise [3].
Primary (acute) or recent HIV infection can be difficult to diagnose since it is asymptomatic or presents as a common febrile illness with non-specific symptoms [4]. Typically patients are highly infectious during this acute phase due to the enormous viral burden in blood and genital secretions [4, 5]. In the United States, it has been estimated that one quarter of recently infected patients remain unaware of their status, and are therefore considered significant contributors to onward transmission of HIV.
Since it is essential to prevent such further transmission as much as possible, the identification of primary HIV infections is clearly a matter of great importance, not only at the level of overall public health, but also for identifying all individuals who may benefit from early therapeutic intervention.
Assessing and testing
Voluntary HIV counselling and testing (VCT) has become an effective public health tool, providing access to confidential HIV prevention and care to individuals who might otherwise ‘shy’ away from HIV intervention [7]. Many people who are concerned about HIV and AIDS will not immediately seek testing at their local medical facility because of their concerns regarding stigma and discrimination. The anxiety of waiting during a period of one to seven days for test results, with the fear that the test may be positive, means that many people do not return to collect their results, even from genito-urinary medicine (GUM) clinics where they do have a degree of anonymity.
In May 2007, UNAIDS and WHO released guidelines on HIV testing and counselling in health facilities, recommending VCT alongside provider-initiated testing in all healthcare settings. The VCT model of pre-test discussion, HIV testing, and post-test discussion emphasises the importance of client-centred care pathways. By understanding their HIV status, individuals are able to gain early access to specific treatment, care and counselling, prevent transmission, and plan for the future [7]. The 2008 European Guideline on HIV testing followed up on the WHO guidelines to describe the primary goals of HIV testing in clinics dealing with sexually transmitted infections (STIs) as:
• To provide pre- and post-test counselling for HIV-negative individuals at risk of HIV transmission;
• To reduce the transmission of HIV and other STIs to others following a diagnosis of HIV;
• To identify HIV-infected individuals as early as possible and immediately link them into appropriate medical management and care;
• To initiate partner notification with counselling, testing and referral to prevention services or partners of HIV-positive persons [8].
Key to community HIV testing is the innovative use of rapid point-of-care tests. Although enzyme-linked immunosorbent assays (ELISAs) are still the most widely used diagnostic test for HIV, there are new simple/rapid tests available that are more suited to situations where no or limited laboratory facilities are available. The use of rapid tests increases the overall capacity to both test and provide results in the community setting, and is recommended by the WHO as a component for the scaling up of HIV testing and counselling services [9]. However, the disadvantage of the point-of-care tests currently available is that they only detect HIV antibodies and not antigen, thus making them less suitable for the detection of early, primary HIV infection. The p24 antigen is produced during the first few weeks of HIV infection and is detectable before HIV antibodies are produced, so making it an ideal marker as an aid for early HIV diagnosis.
HIV antibody assays, including most sensitive third-generation tests, are limited in their ability to detect acute infections of HIV as they do not target viral components, nor do they identify infection during the pre-seroconversion phase and can only partially identify per-seroconversion cases. In order to address the challenge of having tests that are appropriate for use during this period, fourth-generation screening assays have been developed. These have been shown to shorten the duration of the “diagnostic window” by detecting HIV antibodies and HIV-1 p24 antigen simultaneously [10]. The 2008 European Guideline on HIV testing recommends the use of “fourth-generation screening assays that simultaneously test for anti-HIV-1 antibodies and HIV-1 p24 antigen, as well as anti-HIV-2 antibodies as screening tests in European STI clinics” [8]. Until now, commercially available fourth-generation HIV tests existed only in ELISA format and were “combined” assays in that they did not differentiate between the two markers but only gave a single result. They thus lack the capability to specifically identify the status or phase of infection, be it an acute infection (incident case) or serological positive (prevalence case). Despite the increasing use of laboratory-based fourth generation assays for the routine diagnosis of HIV infection in the developing world, their utility is still severely limited by the lack of suitable laboratory infrastructure and the costs of the tests. Another inherent limitation to laboratory testing is the long turn-around time before results are available and the consequent significant “loss to follow up”, which occurs especially in remote areas when patients do not obtain their test results [11].
By simultaneously detecting for p24 antigen and HIV antibodies, fourth-generation HIV tests increase the ability to detect and diagnose primary HIV infection. The Determine HIV-1/2 Ag/Ab Combo is the first single rapid immunochromatographic test to provide simultaneous and differentiated detection of HIV-1 p24 antigen and human antibodies to HIV-1/2. The new test is capable of detecting HIV infection several days earlier than HIV antibody-only tests. Providing significant advantages over antibody-only point-of-care tests and lab-based EIA and ELISA fourth-generation HIV testing, the new test requires only a small amount of serum, plasma or whole blood, and can use capillary blood from a finger prick which is quick, safe and virtually painless. Once the sample is applied to the simple test device, reliable results are available in just 20 minutes. Engineered in a robust format for performance anywhere in the world, the new test is suitable for use in the areas of the world where HIV is most prevalent, for example sub-Saharan Africa and East Asia. With no need for refrigeration, power or water to run the test, it is easy to transport and can be stored at room temperature. The simple foil strip format and packaging requires limited storage space and minimises waste.
Determine HIV1/2 Ag/Ab Combo
The performance of the new test was evaluated both in-house and at nine external clinical sites in Africa, Asia, Europe and Latin America. A total of 1179 positive and 2343 negative specimens were tested including samples from patients with and at risk of HIV infection, blood donors and from other clinical categories. Thirty three commercial seroconversion panels were also used. The analytical sensitivity determination of the assay p24 antigen cut-off was carried out using the EFS Antigen panel. The studies were designed for two types of specimens: retrospective (frozen serum/plasma) samples and fresh prospective (whole blood and serum/plasma) samples. Using samples from 1179 patients at the chronic stage of infection, the diagnostic sensitivity of the new test was calculated to be 100% [Figure 1].
The capability of the test to detect early infection was demonstrated using 33 commercial seroconversion panels. The results show that Determine HIV-1/2 Ag/Ab Combo is able to identify infection on average five days earlier (range 2-20 days) than third-generation antibody tests.
Figure 2 demonstrates how, when panel BBI-AS was tested on the new test, the p24 antigen was detected on day 12, i.e. seven days before the HIV antibodies can be detected.
Of 117 samples (pre- and per- seroconversion) from primary HIV primary infected patients, assayed by both the new rapid test and commercially available CE-marked fourth-generation EIA tests, it was found that the new test identified 92.3% of samples [Figure 3]. With a performance comparable to those of fourth-generation EIA test systems, the new test is excellent for testing patients at the chronic stage of infection; in addition, the new test gives an improved detection of early HIV infections. The overall diagnostic specificity for markers is 99.23% and 99.66% for HIV antibodies and HIV-1 p24 antigen respectively [Figure 4].
Global appeal
By detecting all known sub types of HIV and HIV-1 p24 antigen, the new test can greatly help healthcare workers across the world diagnose primary infection, prevent mother-to-child transmission, monitor HIV prevalence and screen blood donations.
The WHO has recognised that the rapid expansion of treatment access in resource-limited settings is beginning to save lives, improving quality of life, and contribute to the rejuvenation of households, communities and societies [7]. According to UNAIDS, the number of people using HIV testing and counselling services has quadrupled in the past five years. However, worldwide, only 12% of people who want to be tested are currently able to be tested. Calling for a move towards universal access to HIV prevention, treatment, care and support, the WHO and UNAIDS are working towards a sustainable and effective fight against the HIV epidemic. Programmes such as VCT and other interventions for HIV prevention, treatment and care that are backed by organisations such as WHO and UNAIDS, as well as the UN Millenium Development Goals (MDG), are starting to show results. In a number of countries, the level of HIV prevalence is finally, actually decreasing; rapid HIV diagnostics play a significant role in this trend [7].
References
1. UNAIDS 2007. 2007 AIDS epidemic update www.unaids.org/en/KnowledgeCentre/HIVData/EpiUpdate/EpiUpdArchive/2007/default.asp
2. Barré-Sinoussi F, Chermann JC, Rey F et al. Isolation of a T-lymphotropic retrovirus from a patient at risk for acquired immunodeficiency syndrome (AIDS). Science 1983; 220: 868-871.
3. UNAIDS (2008) 08 Report on the global AIDS epidemic: executive summary ttp://data.unaids.org/pub/GlobalReport/2008/JC1511_GR08_ExecutiveSummary_en.pdf
4. Hoffmann C, Rockstroh JK and Kamps BC. HIV Medicine 2007; Flying Publisher, Paris, France.
5. Pilcher C, Eron JJ, Galvin S, Gay S and Cohen MS. Acute HIV revisited: new opportunities for treatment and prevention. The Journal of Clinical Investigations 2004; 113(7): 937-945.
6. Lyons MS, Lindsell CJ, Hawkins DA, Raab DL, Trott AT and Fichtenbaum CJ. Contributions to early HIV diagnosis among patients linked to care vary by testing venue. BMC Public Health 2008; 8: 220.
7. WHO 2002. Increasing Access to HIV Testing and Counselling www.who.int/hiv/pub/vct/en/IncreasingReportE.pdf
8. M Poljiak, E Smit, J Ross (2008) 2008 European Guideline on HIV testing
9. MDG 2007. Millennium Development Goals Report 2007 www.un.org/millenniumgoals/docs/UNSD_MDG_Report_2007e.pdf
10. Saville R, Constantine NT, Cleghorn FR, Jack N, Bartholomew C, Edwards J, Gomez P and Blattner WA. Fourth-generation enzyme-linked immunosorbent assay for the simultaneous detection of human immunodeficiency virus antigen and antibody. Journal of Clinical Microbiology 2001; 39: 2518-2524.
11. Respess RA, Rayfield MA and Dondero TJ. Laboratory testing and rapid HIV assays: application for HIV surveillance in hard-to-reach populations. AIDS 2001; 15 Supplement 3: 549-559.
The author
Thierry Guidasci, PhD
International Product Manager – HIV
Inverness Medical, Bedford, UK
www.determinetest.com
Human papillomavirus associated with higher risk of new HIV infection
Infection with anal human papillomavirus (HPV), the virus that can cause anal and cervical cancers, is associated with a higher risk of new HIV infection in previously HIV-negative men who have sex with men (MSM), according to new research from the University of California, San Francisco, USA reported in the journal AIDS.
In previous studies, other sexually transmitted infections have been associated with a higher risk of HIV infection and HPV is the most common sexually transmitted infection. In this recent study, the 1400 participants were part of the EXPLORE trial, a large clinical trial with sites in Boston, Denver, New York and San Francisco to test the efficacy of a behavioural intervention for HIV-negative MSM. Risk factors were calculated from those men who became HIV-infected over the course of the trial; infections were identified by blood tests.
The researchers think that HPV enhances susceptibility to HIV infection through two mechanisms. Anatomically, the virus causes anal lesions. These lesions bring blood vessels closer to the surface and also the lesions’ skin layer is thinner and more easily shredded, which frequently causes bleeding. These disruptions of the mucosal barrier could allow easier entry for HIV. In addition, HPV activates the immune system. The inflammatory cells recruited to the HPV lesions—dendritic cells, macrophages and CD4 T cells—are the immune cells most susceptible to HIV infection.
HPV vaccine has been found effective in protecting women from the HPV virus. To date, the focus of attention on HPV has been almost exclusively on its key role in causing squamous cell cancer. This study points to another important means by which HPV infection may be associated with morbidity and mortality, namely through potentiation of HIV infection. A direct role for HPV in this process will need to be confirmed in additional studies; understanding the mechanisms involved will also require additional work. Clinical trials testing the effectiveness of the HPV vaccine among men who have sex with men are currently under way.
news.ucsf.edu/releases/cancer-causing-virus-associated-with-higher-risk-of-new-hiv-infection/
