AN ESTIMATE OF THE PREVALENCE OF HUMAN-IMMUNODEFICIENCY-VIRUS INFECTION IN ENGLAND AND WALES BY USING A DIRECT METHOD

Knowledge of the number of human immunodeficiency virus (HIV) seroposi tive people in a country and of their distribution in different transm ission categories is important for health care planning, for risk esti mations and for targeting public health interventions. We used data on seroprevalence of antibody to HIV in defined subgroups of the populat ion attained from unlinked anonymous HIV testing surveys and combined these with estimates of the respective sizes of these subgroups from a n interview study on sexual attitudes and lifestyles. Seroprevalence i n those subgroups not covered by the HIV testing surveys was derived f rom a series of assumptions and approximations. The estimated numbers of HIV seropositive subjects in each subgroup were added to give an ov erall total for England and Wales at the end of 1991. The overall esti mate was 27180 HIV seropositive people, with lower and upper bounds of 20200 and 34300 respectively. Homosexual and bisexual men were estima ted to constitute about half of the total number who were seropositive , and heterosexually infected people constituted approximately a quart er. The greatest numerical uncertainties applied to the number of HIV seropositive men who have had a male partner, but not in the last 5 ye ars, and to the number of HIV seropositive heterosexual men and women who have no recognized risk behaviour. Overlap between the various sub groups defined by unlinked anonymous testing programmes is substantial , but could partly be adjusted for with data from the interview study. The estimates of this study are in the same range as those made earli er with this and other modelling strategies.