Throughout the world, the above routes of transmission have accounted for the overwhelming majority of HIV infections, but there has been considerable concern about other theoretical modes of transmission, especially through “casual” contact with HIV-infected persons, exposure to saliva or aerosols, or insect vectors. More than 700 nonsexual household contacts of adults or children with HIV infection have been evaluated in prospective studies. In thousands of person-years of close contact, including sharing bathroom and kitchen facilities, and frequent personal interactions including kissing and hugging, no transmission other than sexual or perinatal has occurred.

HIV has been isolated from saliva but less frequently than in blood, and at least two definite cases of HIV transmission through kissing have been reported in the United States. In addition, a case report of HIV transmission between siblings suggested a bite as the possible route of transmission, although the precise mode of transmission in this case was unclear because seroconversion was not documented and the bite did not break the skin or result in bleeding. Because saliva can contain other pathogenic organisms, appropriate precautions for health care and dental workers remain important, including universal precautions if gross contamination with blood is present.

Aerosols have not been reported to transmit blood-borne pathogens such as HIV or hepatitis B in health care or other settings. Extensive laboratory and epidemiologic studies of hepatitis B have failed to detect HBsAg in respirable particles in air samples in dental operatories or dialysis units during procedures on infected patients when aerosols were generated. Because the concentration of HBsAg in body fluids is much higher than that of HIV, it is unlikely that HIV would be detected. Extensive laboratory studies have failed to demonstrate replication of HIV in insects that were fed high concentrations of HIV or injected with HIV-contaminated blood. Epidemiologic studies in the United States, Haiti, and Central Africa show no evidence of insect-borne HIV transmission.

The possibility of previously unrecognized modes of HIV transmission cannot be entirely excluded, but they are likely to be rare, if found.