HIV proof-of-transmission tests may be unreliable

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ucl.ac.uk/medicalschool/infection-immunity/" target="_self">UCL Infection & Immunity

A study co-written by Professor Deenan Pillay, Director of the Centre of Virology, UCL Infection & Immunity, and the Health Protection Agency (HPA), has cast doubt on the viability of using certain types of virological evidence to prove HIV transmission in criminal cases.

The article, published in the 'British Medical Journal'‚ cautions that viral phylogenetics‚ the study of the relationships between viruses from different individuals, cannot be used as proof of transmission.

Several criminal cases in the UK brought against individuals accused of infecting their sexual partner(s) with HIV have resulted in convictions. It is known that since HIV-1 evolves very rapidly, strains of the virus which are very similar to each other are likely to have a common source of infection.

Professor Pillay warns, however, that viral sequence evidence is not as conclusive as DNA fingerprinting for example. The study advises that virological evidence should always be used in conjunction with clinical and epidemiological evidence - the probability that viruses from two individuals have a common origin can only be estimated when compared with other strains in the population.

Similarities in two cases of a virus may occur due to reasons other than a common source of infection, such as parallel evolution of the strains. One scenario where this is possible is the independent development of drug resistance mutations, as shown by previous research.

The study, conducted in collaboration with researchers from the University of Edinburgh and the Royal Free Hospital, also points out that identifying that two cases of the virus are linked says nothing about the direction of transmission (who infected whom). It is also difficult to rule out the possibility of transmission to both individuals from a third party, as it is unlikely that all the sexual contacts of the individuals concerned will be available for testing.

Professor Pillay, who is a member of the UK Expert Advisory Group on AIDS (EAGA), said: "The criminalisation of HIV transmission risks a reduction in uptake of HIV testing, which is bad for those infected with the virus, as well as for the community at large. Our assessment of the evidence base for such criminalisation cases provides another reason for caution in taking such cases forward".

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By Jenny Goepel