Investigators in Taiwan have identified a case of HIV transmission due to a knife fight. The case is reported in the online edition of AIDS Research and Human Retroviruses. The researchers used phylogenetic analysis to link the virus in the attacker and victim, and they also argue that new HIV testing technology allowed them to determine the direction of HIV transmission.

Most cases of HIV infection have occurred as a consequence of unprotected anal or vaginal sex. However, the virus can also be spread through blood-to-blood, and there are reports of HIV being transmitted during fist fights.

Now investigators have found compelling evidence of HIV transmission from one individual to another during a knife attack.

The attack occurred in September 2008. The attacker was a 42 year old who had been diagnosed HIV-positive in December 2005. His CD4 cell count was 445 cells/mm3 and his viral load was 57,700 copies/ml. He was not taking antiretroviral therapy and had a history of injecting drug use.

He attempted to rob a 69-year-old man and in the ensuing fight both sustained serious injuries and were hospitalised. The victim received blood transfusions during surgery after the fight. He was married with children, and reported no history of injecting drug use or any other HIV risk behaviour. In October 2008 both he and his wife tested HIV-negative.

However, in February 2009 the victim, but not his wife, became HIV-positive.

His blood transfusion was ruled out as the mode of transmission as all the donors were HIV-negative.

Therefore, investigators hypothesised that the individual's infection was due to blood-to-blood contact during the knife attack.

To test this theory blood samples were obtained from both the attacker and the victim. Both individuals were infected with the same HIV subtype (HIV-1CRF07_BC).

Phylogenetic analysis of both the env and pol regions also showed that the virus in the two individuals was very closely related.

The investigators also believe that they have proof of the direction of HIV transmission. Levels of HIV-IgG were measured in the two individuals. Levels of IgG increase with the duration of HIV infection.

Levels of IgG increased in the victim and, write the investigators, "provided…the evidence for the direction of HIV-1 transmission from the robber to the victim."

They add, "we conclude that this HIV transmission most likely resulted from blood-to-blood contact during a fierce fight…it is the first case providing HIV-1 seroconversion data as evidence to establish the direction of HIV-1 transmission."