DNA Strain Analysis Debuts in Murder Trial

A Louisiana doctor was found guilty Friday of attempted murder for injecting a former lover with HIV-infected blood in the first criminal case in the United States that used a DNA analysis of HIV strains. Experts say similar evidence could be used whenever the source of a fast-mutating virus is at issue, and the case points to the need for an explicit set of rules governing the use of such evidence in the courts.

The Louisiana case began in 1995 when Janet Trahan Allen, a nurse in Lafayette, accused Richard J. Schmidt, a local gastroenterologist, of deliberately infecting her with HIV and hepatitis C. She claimed that after she had threatened to break off their decade-long affair, Schmidt infected her with tainted blood in place of one of her regular vitamin injections. The blood, the state argued in court, came from two of Schmidt's patients, one of whom had hepatitis C and the other had HIV.

The prosecution arranged for an analysis of the HIV strains in blood samples from Schmidt's HIV-positive patient and from Allen. Michael Metzker, at the time a graduate student in the laboratory of Richard Gibbs at Baylor College of Medicine in Houston, compared the gene sequences of the strains to see how closely related they were, using a technique called phylogenetic analysis. He reported that the strains from the two samples were more closely related to each other than to a set of controls from other HIV-positive patients in the Lafayette area. The prosecution also presented evidence that the seven men with whom Allen had sex between 1984 and 1995--including Schmidt--had all tested negative for HIV.

Defense witness Bette Korber, head of the national HIV database at Los Alamos National Laboratory in New Mexico, told the jury, however, that the similarity between the strains could have been mere chance. A search of a database of HIV strains in Louisiana had turned up two pairs of infections that appeared to be more closely related than the patient's and Allen's, she said. Those infections, she testified, had no known or probable links to each other.

Both sides say similar cases are bound to arise, and guidelines like those developed by the National Academy of Sciences in 1996 to govern DNA fingerprinting are needed. Korber says such requirements should include a thorough investigation of all possible routes of infection, blind testing of samples, and clear records of the chain of custody of samples. She says juries should also be told explicitly that phylogenetic analysis cannot prove direct transmission. Schmidt, who will be sentenced in the next month, faces 15 to 50 years in prison. His lawyers plan to appeal.