Convictions for HIV transmission that rely on phylogenetic evidence are 'unsafe', says BMJ editorial

Convictions for the reckless transmission of HIV that rely on phylogenetic evidence are “inherently unsafe”, an editorial in the September 7^th edition of the British Medical Journal argues. The authors, three expert virologists, “advise caution” when interpreting phylogenetic data that appear to show an HIV transmission link between individuals, “because the strength of any apparent linkage between viruses will never approach the degree of certainty generally expected of ‘DNA’ data in criminal court, which juries are more familiar with.”

An article in the August edition of Nature Medicine also highlights how the increasing trend to criminalise HIV transmission in several African countries is based upon “questionable science.”

A number of individuals have been prosecuted for the reckless transmission of HIV in the UK in recent years. There has been widespread concern amongst both health professionals and HIV community groups that these prosecutions, and the resulting convictions involving lengthy custodial sentences, are undermining HIV prevention efforts, deterring both the disclosure of HIV status and the uptake of HIV testing.

Virological evidence, obtained from the defendant and complainant, has been used in these cases to show that the defendant was the source of the complainant’s infection. In the recent UK cases, the prosecution has attempted to use similarities in HIV’s phylogenetic sequence in a way that is akin to DNA fingerprinting.

“This analogy is seriously misleading for several reasons,” write the authors, “and when attempting to establish that transmission occurred between specific people virological evidence should be used with caution and only in conjunction with the clinical and epidemiological evidence.”

The editorial was written by Professor Deenan Pillay of University College, London, Dr Anna Maria Geretti of the Royal Free Hospital, London, and Professor Andrew Leigh-Brown and Andrew Rambaut of the University of Edinburgh, and takes into account a discussion at a recent meeting of the UK's Expert Advisory Group on AIDS (EAGA), which advises the government on scientific aspects of HIV.

They also note that conclusions about the apparent relationship between strains of HIV found in two individuals “depends both on the assumptions made in the statistical analysis and the data made for analysis.” They note that two seemingly linked strains must not be examined in isolation be compared to other strains.

“There are serious limitations on what can and cannot be inferred using phylogenetics alone and, in our view, a conviction that relies on such evidence to establish transmission is inherently unsafe”, stress the authors who emphasise “expertise should be sought before undertaking such analyses.”

Identifying an apparent linkage between HIV in two people “says nothing” about the direction of transmission, note the authors. Nor, without the testing of all sexual contacts is it possible to rule-out transmission from the third-party.

Coinfection, superinfection, and the evolution of drug-resistant strains of HIV can all make interpretation of phylogenetic evidence more complex.

The authors conclude that “the only safe use of virus gene sequences is in circumstances where the genetic differences between viruses are sufficient to make linkage between two people doubtful.”

Prosecutions for the transmission of HIV have also occurred in several African countries, and a report in the August edition of Nature Medicine cautions against the use of phylogenetic evidence in these settings. Jusef Azad if the National AIDS Trust in the UK commented, “in the absence of really clear scientific evidence as to who infected whom, there will always be an assumption that those categorised as undesirable by society are guilty of infecting other people.”

Nor is there any evidence that prosecutions help prevent new HIV infections. Jonathan Berger of the AIDS Law Project in Johannesburg commented, “they make law makers feel good, but they have very limited positive benefits for the public”, often just further stigmatising an already stigmatised illness.

Dr Anna Maria Geretti, one of the authors of the BMJ editorial, has contributed an essay on the use of phylogenetic testing in HIV prosecutions to the NAM book Criminal HIV Transmission. To order a copy click here.