Educating (about) RITA: Scientific accuracy and HIV prosecutions

Yusef Azad from NATProsecutions for ‘recklessly transmitting’ HIV to sexual partners have taken place since 2001 in Scotland and since 2003 in England and Wales.  NAT along with most other HIV organisations oppose such prosecutions – vast numbers of people are ‘reckless’ in their sexual behaviour, and it is most often the undiagnosed who pass HIV on to others. To single out just a few people with an HIV positive diagnosis (and prosecutions are very rare) for the full force of the criminal law is to scapegoat a handful of individuals for a wider failure of the UK population in safer sex. But while prosecutions continue, there is a lot we can do to minimise their harm and limit their impact. One success has been agreeing guidelines with the police and Crown Prosecution Service on when and how someone can be investigated and prosecuted. The guidelines have ensured that investigations and prosecutions take place with some understanding of HIV and some care over the evidence, which can be used to prove guilt.  

In the early days of prosecutions there were cases where it had clearly been assumed that the sexual partner who had had an HIV positive diagnosis must have been the one to pass HIV on to the complainant. But how can one know that for sure? HIV transmission is an invisible biological event – no one witnesses it, all that is ever visible (at least to the two – or more - involved!) is sex, whether protected or unprotected. And we know even in unsafe sex the chance of HIV being transmitted is always relatively low. One of the facts we needed to explain to police and prosecutors was that HIV transmission is not an inevitable result of sex between an HIV positive and an HIV negative person - far from it. If the complainant has had other sexual partners then we need also to consider the possibility that one of them may have transmitted HIV to the complainant (even if they were undiagnosed at the time).  

The prosecution has to prove that it can only have been the accused who passed HIV on to the complainant. To do this, scientific evidence has been used. One piece of evidence is phylogenetic analysis, which compares the viruses of the complainant and the accused to see if they are similar. Early on this evidence had been seriously misused in court cases. It had been claimed that a ‘match’ between the two virus samples meant that the accused was the one responsible for passing on HIV. But it did nothing of the sort. A match could also mean that it was the complainant who passed HIV on to the accused, or that both were infected by someone else, to give just two possible alternative explanations. NAT and NAM commissioned experts to write a paper explaining in detail how evidence had been misused and setting out its proper value as evidence (‘HIV Forensics’ see www.nat.org.uk). This work was included in the Guidance on prosecutions published by the Crown Prosecution Service and the result has been a decline in the number of cases getting to court. If a complainant has had any other sexual partners during the relevant period, it is necessary to trace and test them all and show that no one else could possibly have passed on HIV to the complainant. This is not an easy thing to do.

This showed how important it is to ensure scientific evidence is used carefully and accurately in court and that people don’t claim that a certain test result proves someone’s guilt when it doesn’t do so. The unfortunate fact in the case of phylogenetic analysis was that some people had already gone to prison on the basis of scientific evidence, which had not been properly understood and explained to the court. NAT was keen to ensure that this did not happen again – we were on the look out for other scientific tests, which might be relevant to prosecutions and where care is needed in how they are interpreted. Sure enough one came along – RITA testing – and NAT has just published a report warning about how this test had to be understood in the context of prosecutions (‘HIV Forensics II: Estimating the likelihood of recent HIV infection - Implications for criminal prosecutions’ www.nat.org.uk).  They haven’t yet been used in court cases – but we weren’t going to wait until someone was wrongly convicted. It is important to be prepared and produce guidance now as to how RITA tests can and cannot be interpreted.

What is a RITA test? It is a test to find out whether or not someone has probably been infected recently with HIV. These tests have been rolled out in the UK and elsewhere because we need to find out more about the rate at which HIV is spreading in the population. Up until now this was difficult because someone diagnosed with HIV could have been infected any time from a few weeks ago to over a decade ago. There are a number of different types of RITA test but all look in their different ways for signs that the HIV infection is recent. The basic idea is to look at the immune response of the individual to HIV infection - this immune response changes and develops in the early stages of infection before stabilising. So the RITA test looks for indications of an early, as opposed to stabilised, immune response.  The test used in the UK identifies whether the infection is likely to have taken place in the previous 5 months, or before. The test does not give any more specific timing than this recent/not recent distinction.  

‘NAT has succeeded in securing new advice from the CPS warning prosecutors of the limitations of RITA test results as evidence.’

Whilst a number of countries are now using RITA tests on HIV positive samples, the UK is unusual in being the only place where those diagnosed HIV positive are also being told the result of the RITA test. It isn’t hard to see the possible relevance for criminal prosecutions. Someone given the RITA test result and told their infection is probably recent will find it much easier to jump to a conclusion as to who passed on HIV to them; e.g. If I have only had sex with one person in the last five months and I’m told my infection is recent, I am likely to conclude ‘well then, it must be that person who passed on HIV to me’!

But this is not necessarily the case, and NAT’s report explains why.  RITA tests are not designed to give individuals reliable information on the timing of their infection – they are designed for epidemiologists to look at the spread of HIV in a population.  The cut-off point for an infection being recent is based on the average response rate amongst people with HIV – but for any average there will be individuals who respond below or above the average rate. There are plenty of examples of people having ‘recent infection’ results where it can be demonstrated by other means that they could not possibly have been infected recently.  

Already NAT has succeeded in securing new advice from the CPS warning prosecutors of the limitations of RITA test results as evidence, and we hope the report will also be used internationally to prevent miscarriages of justice. It is as important that RITA test results given to individuals in the UK are given carefully, emphasising that any indication of recent infection is only approximate and a probability, not definite. Healthcare workers need training in providing these results if they are not to fuel unwarranted accusations, and written patient literature on the test (such as that recently produced by the Health Protection Agency) should be also given to the patient to make clear the limitations of RITA test results.
It will take time to change the culture of blame, which still persists around HIV - but we can – at least and as a start – prevent science being abused and misunderstood as a basis for unfounded accusations. NAT hopes our report will contribute to a saner and evidence-based approach to prosecutions - such an approach may one day end prosecutions altogether. 

Words by Yusef Azad