Objective: To describe the clinical, epidemiological and molecular evidence for transmission of HIV-1 infection from a person with unrecognized HIV infection to a family member in two unconnected families where the route of transmission could not be conclusively determined.
Design: Case studies, molecular analysis of viral strains and a clinical and laboratory investigation of risk factors for transmission.
Setting: State referral centres for HIV/AIDS in two Australian teaching hospitals.
Results: Previously unrecognized HIV-1 infection was diagnosed in two unconnected females following blood donation in different Australian cities. Initially, no source of infection was identified but subsequently HIV-1 infection was diagnosed in the sister of one case and the adult son of the other. Using nucleic acid-based methods, it was demonstrated that one index case and her sister were infected with highly homologous 'Russian-type' HIV-1 subtype A, and the other index case and her son were infected with highly homologous HIV-1 subtype E (CRF01_AE). Sexual history taking from the sister and the son of the respective index cases revealed prior sexual partners from geographical areas in which the corresponding subtypes are known to be prevalent. Extensive history taking, cross-validated by independent reviewers, found no evidence whatsoever that any form of sexual contact or known blood contact could explain the HIV-1 infection in the two index cases. However, there was evidence that some form of domestic contact involving unperceived blood transfer may have occurred.
Conclusion: Intra-familial transmission of HIV-1 infection should be considered when a source of HIV-1 infection cannot be determined.