Hiv Testing And The Care Continuum
HIV diagnostic testing is the crucial first step in the HIV care continuum. Establishing a diagnosis of HIV has important implications for both HIV treatment and prevention. Accumulating evidence shows that persons living with HIV who take antiretroviral therapy without interruption have better clinical outcomes and reduced HIV transmission. Based on Centers for Disease Control and Prevention estimates for 2016 in the United States, persons living with HIV who were unaware of their HIV diagnosis accounted for an estimated 37.6% of all new HIV transmissions during that year. The highest HIV transmission rates occur among persons with acute HIV infection who are unaware of their diagnosis.
Introduction And Guiding Principles
A request was made by the Federal/Provincial/Territorial Committee on AIDS for the Public Health Agency of Canada to develop guidelines on HIV testing that reflect the realities facing care providers and their clients, as well as advances in HIV testing policy and practice. To inform the development of this guide, the Agency commissioned a literature review and consultations with key stakeholders, including people living with HIV/AIDS and other affected populations, academics, nurses, physicians, professional associations, non-governmental organizations, policy-makers, community workers, and legal and ethical experts. As a result, the recommendations outlined in the guide are based on the most up-to-date evidence and expert opinion.
Testing Reports For Health Care Providers
The HIV Diagnostic Testing Algorithm includes combinations of HIV test results that may be unfamiliar to health care providers. Therefore, in addition to the results of all tests, the laboratory report that is returned to the ordering clinician should include a final interpretation statement and, when appropriate, recommendations for follow-up testing. A list of the different combinations of test results and the NYSDOH recommended interpretation statements is provided in Attachment 2. Providers may request that preliminary HIV test results be reported to them prior to completion of the algorithm. Additional information on currently available tests appropriate for the algorithm may be found on the NYSDOH web site.
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Factors That Increase Risk For Hiv Infection
Sexually active but no history of being tested for HIV.
Use of shared drug equipment with a partner whose HIV status is unknown.
Unprotected anal or vaginal intercourse with a partner whose HIV status is unknown.
Multiple and/or anonymous sexual partnering.
For men, a history of sex with other men.
Diagnosis of other STI, hepatitis B or C.
Sexual activity, sharing of drug-use equipment, or receipt of blood or blood products for people originating from, or who have travelled to, regions where HIV is endemic.
Receipt of blood or blood products in Canada prior to November 1985.
Where To Access Testing Services
Standard HIV testing can generally be accessed through any health provider across the country. Each province is responsible for licensing the laboratories that provide HIV screening and confirmatory testing in its jurisdiction. In general, all provincial Public Health Laboratories provide both screening and confirmatory testing. Reference and specialized services, when required, are provided by the National HIV Reference Serology Laboratory after consultation with the provincial laboratory. It is advisable to contact your testing laboratory to confirm the specimen collection details.
Anonymous or POC testing locations can be found by calling a local HIV/AIDS hotline .
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Nature Of Algorithm/testing Strategy
A testing algorithm for serologic diagnosis of HIV-infection is the sequence in which assays are performed to detect HIV antibody in a body fluid. The most common referenced testing algorithm employs an EIA to screen specimens with those found to be positive then confirmed by WB testing. This so-called conventional algorithm has several limitations :
WB is expensive and requires technical expertise.
WB often yields indeterminate results with certain types of specimens with uncertain diagnostic significance, e.g., hyperimmunoglobulinemia specimens.
Both ELISA and WB are time consuming and require a well-equipped laboratory infrastructure.
Various combinations of tests can be used: combinations of HIV EIAs combinations of rapid tests or an EIA in conjunction with rapid tests. The choice of strategy and of HIV tests should be determined by the quality of the tests and by the practicality of their implementation, logistics, and the cost-benefit analysis. Figure 1, depicts the WHO/UNAIDS testing strategies which can be adopted in diverse settings
In the WHO/UNAIDS testing strategies I III, as applicable relative to testing objective or diagnostic indices .
Early Hiv Test Reactivity And Terminology
The CDC and Association of Public Health Laboratories document, based on several CDC-related studies, have outlined the sequence of laboratory markers turning positive following acquisition of HIV . The CDC/APHL document and the Adult and Adolescent ARV Guidelines have defined the following laboratory-based and clinically relevant terms related to acute HIV. Note that some of these terms are not standardized and alternative terminology, such as primary HIV infection, is often used.
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New Tests New Wrinkles In Hiv Algorithm
Three yearsincluding a total eclipse of the sunhave sped by since the Centers for Disease Control and Prevention and the Association of Public Health Laboratories recommended a new HIV diagnostic testing algorithm for laboratories. In 2014, the algorithm was seen as bringing HIV test ordering up to speed with the advances in HIV test technology and increasing the accuracy and reliability of HIV screening and diagnosis. Have laboratories made the adjustment, and is the CDC/APHL algorithm proving workable and worthwhile?
Dr. Philip Peters of the CDC Division of HIV/AIDS Prevention. He and others spoke recently about the 2014 HIV testing algorithm and new challenges.
Philip Peters, MD, believes the answers are yesalthough the answers arent simple. Having a robust HIV testing program is really a vital part of HIV prevention, says Dr. Peters, medical officer of the CDC Division of HIV/AIDS Prevention, in an interview with CAP TODAY. Laboratories are successfully adopting the algorithm, but implementation has been met with challenges. Sometimes newly approved tests dont neatly fit into the existing framework or algorithm for HIV testing, he says.
The advanced features of some new HIV tests could have an impact on the laboratory algorithm, said AACC co-panelist Laura Wesolowski, PhD, an infectious disease epidemiologist with the CDC and coauthor of the CDC/APHL Laboratory Testing Guidance.
Hiv Transmission In Drug Users
For people who inject drugs, estimates of the risk of transmission from a contaminated needle range from 0.3% to 4.0%, with several of these estimates falling in the range of 0.7% to 0.8%. Sharing ancillary injecting equipment, such as filters or cookers, has been shown to increase the risk of transmission, even in the absence of sharing needles and syringes. Other factors that have been shown to increase the risk of HIV transmission for injection drug users include: unsafe locations, type of drug and frequency of drug injection. Non-injection drug users are also at risk of HIV infection. Drug use often alters sexual behaviours by increasing risk taking. As well, several drugs have been reported to be independent risk factors of HIV transmission.
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Diagnosis Of Acute Hiv
The laboratory diagnosis of acute HIV-1 infection is most reliably made with a positive HIV RNA with a concomitant negative HIV antibody assay note that with very early acute HIV infection, the p24 antigen assay may be negative . Use of HIV-1/2 antigen-antibody immunoassays will detect HIV at about 17 days after HIV acquisition, which is significantly sooner than with HIV laboratory-based HIV antibody tests, all point-of-care HIV tests, and all in-home HIV tests. Even when using HIV-1/2 antigen-antibody immunoassays, the initial laboratory testing will fail to detect some individuals who have very early acute HIV infection. Thus, for individuals in whom initial HIV-1/2 antigen-antibody testing is nonreactive, but acute HIV is strongly suspected, HIV NAT should be performed. Increased awareness of acute retroviral syndrome by medical providers can help facilitate diagnosis in the early stages of infection. Among persons recently infected with HIV, it is estimated that at least half develop a nonspecific syndrome characterized by fever, myalgia, lymphadenopathy, pharyngitis, fatigue, headache, and rash. Because HIV RNA levels are typically very high in persons with acute retroviral syndrome, an HIV NAT is uniformly positive at this stage of infection.
Stat And Critical Samples Testing
Testing of source patient for needlestick/occupational exposure if warranted. Testing of pregnant women in labour with no prenatal work up and a high risk for HIV.STAT testing should only be requested when it directly affects patient care in an emergency medical circumstance. STAT samples must be shipped separately from routine specimens in a clearly marked package indicating STAT and handled in accordance with the Canadian Biosafety Standards and shipped in accordance with the Transportation of Dangerous Goods Regulations. Failure to ship separately will delay testing.Notify PHO immediately when a STAT sample is sent by contacting our Customer Service Centre at 416-235-6556 / 1-877-604-4567. After-hours STAT testing requires approval by a PHO Microbiologist who can be contacted through the Customer Service Centre.
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Positive Predictive Value And Negative Predictive Value
In contrast to sensitivity and specificity, which refer to the diagnostic ability of a screening test, the predictive value of a test refers to the likelihood that the test will give the correct diagnosis. Positive predictive value is the proportion of patients with a positive HIV result who are correctly diagnosed . Negative predictive value is the proportion of patients with negative HIV results who are correctly diagnosed . Because screening tests are neither 100% sensitive nor 100% specific, the predictive value of tests is also imperfect. It is possible for persons to receive an incorrect result from a diagnostic test: these results are termed false-negative and false-positive test results. It is important to understand that the prevalence of a disease in a community impacts the predictive value of a given test, and predictive values in one study or in one community do not apply to all other settings.
Appendix A: Ethical And Professional Considerations
Policy concerning the ethical and professional roles and responsibilities of care providers is informed by the providers’ respective institutional code of ethics as well as the professional colleges under which they are governed.
The following is designed to complement, not supersede, existing codes of conduct or jurisdictional health policies and regulations or any applicable laws and regulations of the jurisdiction.
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Alternatives For 4th Generation Immunoassays
3rd generation HIV-1/2 immunoassays are capable of detecting IgM and IgG antibodies to HIV and have been used for HIV screening by laboratories for several years. Some laboratories may continue to use 3rd generation immunoassays as their initial screening test, and it is currently acceptable for laboratories to follow the HIV Diagnostic Testing algorithm with a 3rd generation immunoassay as the initial test1. Clinicians should be aware that 3rd generation immunoassays will detect infection early in the seroconversion process, even before a Western blot becomes positive, but they will not detect HIV-1 infection in the acute stage before antibodies are produced. The test results and interpretations in Attachment 2 are based on initial testing with a 4th generation HIV-1/2 Ag/Ab combo immunoassay. If the initial test in the algorithm is a 3rd generation HIV-1/2 immunoassay, the interpretation statements will be slightly different.
Siaya County Kenya: Antenatal Clinics Providing Pmtct Services
Over the study period, 2409 eligible women presented at participating antenatal clinics, of whom 2364 consented to participate in the study . Of these women, 1806 were under 30 years of age, 1792 were married and 1157 had experienced three or more pregnancies. In total, 444 women tested HIV-positive, of whom 426 had a valid LAg and viral-load test . Among these 426 women, 106 tested recent prior to viral-load being considered, with 11 testing recent with a viral-load> 1000 copies/mL.
Following an HIV-positive test result and counselling, 144 of participants subsequently brought a sexual partner to the clinic for HIV testing. Of these 144, two brought in two partners, making the total 146. Among the 146 sexual partners of index cases testing for HIV, 61 tested positive for HIV. Among these 61 HIV-positive partners, 21 subsequently enrolled in the pilot, of whom five were classified as recent. The percentage of partners testing HIV-positive, and being classified as recent, were significantly higher than the corresponding percentages among all non-partner participants .
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Data Collection And Sample Processing
Prior to the commencement of our pilots, all study staff underwent training on good clinical practice, ethics and the handling of confidential information as per our study protocols. Eligible participants were asked to read and sign a consent form and were probed for their understanding. For illiterate participants, study staff read the forms out and sought consent in the presence of an independent witness. Data were collected between February and November 2018.
In all three pilots, anti-HIV-1-positive specimens were classified as either recent or long-standing using a RITA that combined a LAg Avidity EIA ) with information on viral-load, history of prior HIV diagnosis and/or exposure to antiretroviral therapy ) . This RITA gives an indication as to whether or not a person being diagnosed with HIV is likely to have been infected within the last four to six months.
- Inclusion and exclusion criteria for each pilot reflect the routine practice of the facilities within which recruitment was conducted. FSW, Female Sex Workers HDSS, Health and Demographic Surveillance System HTC, HIV Testing and Counselling EIA, Enzyme-linked Immunosorbent Assay.
Challenges In Hiv Testing
4.3.1 HIV Testing in the “window period”
The window period is the time after acquisition of HIV infection when the individual is highly infectious but tests negative on HIV antibody screening because antibodies are not immediately produced. As shown in Figure 4, the timelines associated with the window period have changed with the evolution of more sensitive antibody screening tests. While 1st generation tests detected HIV antibody an average of 60 days following exposure the 4th generation combination tests permit detection of acute HIV infection during the viremic phase. This reduces the window period to approximately 15 to 20 days. Making the diagnosis as early as possible can help prevent onward transmission of the virus, since the person is most infectious during this period. Some jurisdictions provide NAAT testing for high-risk clients , in an effort to identify very early HIV infection.
4.3.2 Indeterminate results during the window period
4.3.3 Confirmatory Testing
The Western Blot assay is not as sensitive as the 3rd and 4th generation screening tests and may yield indeterminate results during the window period. New algorithms employing NAAT as a confirmatory test are currently being evaluated.
Figure 5: Antigen/Antibody detection periods
Figure 5 is a detailed diagram showing the days elapsed, from zero to 360, since the start of HIV infection. The diagram is divided into a sliding scale of four time periods:
4.3.4 Genetic diversity of HIV
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Clinical Laboratory Improvement Amendments Criteria
With a range of HIV diagnostic tests now available, the testing process can occur in a wide range of clinical and nonclinical settings. Most HIV testing is performed in a laboratory setting and the time required to perform the tests varies significantly, but some laboratory tests can be performed in less than an hour. Several point-of-care, single-use rapid tests are now available that can be performed in clinical or nonclinical settings. In the United States, the Centers for Medicare and Medicaid Services regulates all clinical laboratory testing through the Clinical Laboratory Improvement Amendments . As part of this process, CLIA has established a three-level test complexity criteria and this applies to the different HIV testing procedures:
- Waived: These tests are considered simple to perform, low-risk, and can be performed with minimal training specimens do not require centrifugation for testing.
- Moderate Complexity: Although these tests are considered simple to perform the testing involves using plasma or serum specimens, and program participation in an external proficiency testing program.
- High Complexity: These tests involve multiple-step protocols and require trained laboratory personnel to perform, participation in an external proficiency testing program, and frequent checks on quality control.
Evolution Of Hiv Testing
HIV screening and diagnostic tests have been developed, and a variety of testing algorithms have come into use. HIV antibody tests have evolved from first generation HIV-1 viral lysate-based, indirect antibody enzyme immunoassays to third generation antigen-sandwich immunoassays that use synthetic peptide and recombinant DNA derived antigens that represent the immunodominant epitopes from diverse HIV-1 and HIV-2 strains. These third generation enzyme immunoassays have substantially enhanced sensitivity to divergent viral variants and have shortened the infection-to-seroconversion window period by more than 3 weeks compared with first generation tests. Assays have also been developed that detect and quantitate viral antigen and nucleic acids in blood, and in body fluids and tissues .
These assays have seen increasing application in blood and organ donor screening, as well as in clinical diagnosis, prognosis, and therapeutic monitoring and clinicians now have access to a broad and potentially confusing array of test options, each with its own advantages and limitations. Developing testing algorithms and interpretive criteria appropriate to a particular group of patientshigh-risk adults blood, plasma and organ donors recently exposed healthcare workers paediatric patients, and especially in resource limiting settingsposes a challenge, especially as new tests appear with tantalizing claims of enhanced performance .
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Characteristics Of An Ideal Screening Test
The principles that define a good screening test are not unique to HIV infection but apply to medical screening in general. An ideal screening test will accurately identify individuals with the clinical condition of interest, without mistakenly diagnosing individuals who do not have the condition. In addition, use of screening tests is most effective when limited to conditions for which there is available, effective treatment that can directly target the disease and improve prognosis and outcomes.