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Abstract
Objectives Recent Infection Testing Algorithm (RITA) tests are used in public health surveillance to identify the incidence of recently acquired HIV infection. This can then be used to direct public health interventions and evaluate their effects. We aimed to outline how RITA tests may be used in clinical practice with individual patients, as well as highlighting the cautions needed.
Methods The clinical and laboratory aspects of RITA tests have been reviewed in the paper together with their clinical applications.
Results For individuals, RITA tests can help to confirm primary HIV infection and can be useful with elements of partner notification. However, careful evaluation of the result is required and it should be considered in conjunction with the clinical history and findings.
Conclusions There are major epidemiological and public health advantages in using RITA testing but there are also advantages to using the RITA test on an individual basis, provided that it is used appropriately.
- Dermatology
- epidemiology
- genitourinary medicine
- genitourinary medicine services
- HIV
- public health
- Reiters disease
- RITA
- STARHS
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- Dermatology
- epidemiology
- genitourinary medicine
- genitourinary medicine services
- HIV
- public health
- Reiters disease
- RITA
- STARHS
It is estimated that 6658 individuals in the UK were newly diagnosed in 2010 with HIV infection, with 45% of diagnoses being in men who have sex with men and 50% being acquired via heterosexual contact.1
The diagnosis of HIV infection relies on detecting antibodies against the virus. The HIV antibody response evolves as it matures with HIV-specific IgM peaking 1–2 weeks after infection and IgG increasing gradually over several months. The tests generically referred to as serological testing algorithm for recent HIV seroconversion (STARHS) and more recently recent infection testing algorithm (RITA) tests have been developed to detect this maturing picture.2 3 A number of in-house and commercial test formats can be used for RITA purposes (table 1). The avidity assay appears to be one of the more reliable tests.4
Examples of methods used in RITA
RITA tests were initially used in England in unlinked anonymous serosurveillance in men who have sex with men, but became available on a named-patient basis to clinicians via the Health Protection Agency (HPA) in 2008. It has now become a routine component of public health surveillance and an established part of clinical practice in many areas of the UK, with over 50 laboratories and 90 clinics registered with the HPA for RITA testing.5
In 2010, 2183 of all individuals newly diagnosed with HIV had a RITA test performed within 4 months of the initial HIV diagnosis, 15% had results indicating that their infection was most likely acquired within 4–5 months of their diagnosis. This was highest in men who have sex with men (25%) and lower in heterosexual men (8.6%) and heterosexual women (8%).5
Advantages of performing a RITA test
There are major epidemiological and public health advantages in performing RITA tests as they allow determination of the incidence of recently acquired HIV infection, and so differentiate between an increase in HIV infection and increased testing rates. They can identify areas and populations at greatest risk, inform the direction of public health interventions and evaluate their effects.6
For the individual, it can help to confirm primary HIV infection and allow a discussion to take place about antiretroviral treatment, although the evidence for treatment at this stage is limited.7 It has been shown that there are high rates of HIV transmission in early HIV infection,8 and that a higher proportion of sexual partners of individuals with recent infection test HIV positive compared with those with long-standing infection.9 Therefore, identifying HIV-positive individuals in the early time zone gives an opportunity for behavioural intervention and enhanced partner notification. In clinical practice, RITA testing can help direct the partner notification time frame.
When should a RITA test be requested?
Ideally, all samples that test HIV antibody positive for the first time should be RITA tested. This will ensure that all appropriate samples are tested, thereby maximising the chances of detecting recent infections, as time delays will be reduced.
Specimens for a RITA test
In England, RITA testing is performed by the Virus Reference Division at the HPA, Colindale, England, using an HIV avidity test (Abbott Incidence Test; Abbott Diagnostics, Berkshire, UK). The test is processed without charge provided there is a formal agreement between the local clinician, the local laboratory and the HPA. The cost of transporting the sample to the HPA is borne by the local site.
Samples need to be taken within 4 months of a first HIV diagnosis in individuals who are confirmed to be HIV-1 antibody positive.
Ideally, over 0.5 ml of serum is required so blood samples need to be centrifuged and separated. The HPA HIV RITA test request form should be sent with all samples and samples should be transported using standard laboratory procedures. If the sample is to be stored locally for less than 1 week it can be stored at 2–8°C. If the storage is to be for a longer period of time then it must be frozen at −20°C or lower. Freeze-thawing of specimens should be kept to a minimum and must not exceed five times as multiple thawing may affect antibody levels and the test results.3
Interpretation of RITA test results—pitfalls and cautions
The HPA reports the RITA avidity test result in one of four categories (table 2).
Examples of HPA HIV RITA test reports
It is essential to explain to the patient that the RITA tests are aimed at population testing and that there are potential inaccuracies in extrapolating the results to individual patients. This is because there is person-to-person variation in the immune response and HIV antigenicity may vary. It should be explained that the RITA test is unlicensed and it provides a likelihood result only and not a definite confirmation.
Careful evaluation of the result is required and it should be considered in conjunction with the clinical history and findings, HIV exposure risk information, CD4 cell count and HIV viral load. It needs to be interpreted with particular caution in the presence of long-standing HIV infection or AIDS with reduced antibody levels. In these situations the infection can falsely appear to be recent. This is particularly the case with assays that depend on the quantification of antibody, and 2–9% misclassification rates in AIDS patients have been reported.2 A similar response can be seen in patients on antiretroviral therapy and in elite suppressors. The effect of post/pre-exposure prophylaxis is unknown.
Caution is required in the presence of a non-B subtype virus, especially with ‘detuned’ assays. These viral types may show lower binding affinities and extend the recent infection time period leading to an overestimation of recent HIV infection. Other conditions affecting antibody levels can also affect the RITA test such as hyper or hypo-gammaglobulinaemia.
Conclusion
There are major epidemiological and public health roles for the use of RITA testing, but there are also advantages to using the test on an individual basis, provided that it is used appropriately and considered in conjunction with the clinical history and individual circumstances.
Multiple choice questions
Stem 1. A RITA test
| 1. Is mainly used as an epidemiological tool for population monitoring | True/False |
| 2. Can be used to definitely confirm that the patient has acquired HIV within the past 4–5 months | True/False |
| 3. Should be performed every 6 months on all HIV-positive individuals | True/False |
| 4. Is performed on saliva or urine samples | True/False |
Stem 2. The RITA test result
| 1. Is affected by the length of time since the individual acquired HIV infection | True/False |
| 2. May falsely indicate a recent infection in the presence of advanced HIV disease or AIDS | True/False |
| 3. Does not depend on the HIV virus subtype | True/False |
| 4. May help identify the partner notification time period | True/False |
Supplementary materials
Supplementary Data
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MCQ Answers
This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.
Files in this Data Supplement:
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Footnotes
The answers to these questions are published online with this article (http://sti.bmj.com/content/88/4.toc).
Competing interests None.
Provenance and peer review Commissioned; externally peer reviewed.