Main routes of transmission of human immunodeficiency virus (HIV) infection in a family setting in Palermo, Italy.

A cross-sectional seroepidemiologic study was carried out on household contacts and sexual partners of human immunodeficiency virus (HIV) antibody-positive intravenous drug abusers in Palermo, Italy, in 1985 to evaluate factors that influenced HIV transmission. A total of 43 index cases, 36 spouses or heterosexual partners, 28 children, and 55 adult household members were enrolled. None of the household members without sexual contact, who had shared items and facilities and had interacted with the index cases, contracted HIV infection. However, six of 36 sexual partners had antibodies to HIV. It was observed that the risk of HIV infection was significantly associated with the frequency of sexual intercourse with the seropositive partner. Four children were also found to be infected: two had acquired immunodeficiency syndrome-related complex, and the other two were clinically and immunologically normal. Furthermore, one other child had evidence of passive transfer of maternal antibodies. The infection was confined to the younger children (ranging in age from eight months to three years). The data support a high rate of vertical transmission from mother to infant, an intermediate rate of transmission to sexual partners, and no transmission attributable to household contact.