How many persons in Canada have been infected with human immunodeficiency virus? An exploration using backcalculation methods

We have used the technique of backcalculation to estimate the number of persons in Canada who have been infected with human immunodeficiency virus type 1 (HIV) as of July 1989. We first corrected national AIDS surveillance data in Canada for reporting delay and for underreporting. We then used standard Weibull natural history models as well as an alternative progression model in which the hazard of AIDS was dampened in keeping with observed data from large cohorts. Maximum likelihood techniques were then used to derive the infection curve most consistent with these data. Our best estimate based on this alternative progression model, an underreporting rate of 20%, and a logistic infection curve, was that approximately 29,000 persons in Canada had ever had HIV infection as of July 1989. In a sensitivity analysis utilizing less likely assumptions, the estimates ranged from 17,243 to 48,277. Restricting the same backcalculation process to females under the same assumptions, we estimated that approximately 2,900 females in Canada had ever had HIV infection as of July 1989. The best fitting step function infection curve in females appears to be continuing to rise. Given these estimates, it follows that approximately one in ten infected persons in Canada is female. However, females have only accounted for about one in seventeen AIDS cases. These data are in accord with the widespread impression that transmission of HIV to women has occurred more recently and is on the rise across Canada. The current estimate is lower than previous estimates which placed the number of infected Canadians in the 50,000 to 100,000 range. This lowering should not be taken to mean the situation is improving; rather, the early estimates were simply too high having been based on inadequate data and a rudimentary understanding of the natural history of HIV. Backcalculation is an excellent technique for modelling the incidence of HIV infection several years in the past, but it is not reliable for the most recent few years. A significant increase in HIV infection rates may have occurred in the past few years and it would be beyond the capacity of backcalculation to detect. Backcalculation and unlinked cross-sectional specimen surveys together have the potential to provide an effective means of monitoring the HIV epidemic.

Geographic and birth cohort associations of Kaposi's sarcoma among homosexual men in Canada

The authors conducted an analysis of all 677 cases of Kaposi's sarcoma among the 3,047 cases of acquired immunodeficiency syndrome diagnosed in homosexual/bisexual men in Canada between 1980 and 1989. The proportion with Kaposi's sarcoma declined from 32.2% during 1980-1985 to 15.0% in 1989. The proportion with Kaposi's sarcoma was significantly higher in primary epidemic centers (Vancouver, Toronto, and Montreal) and in men in the 1945-1954 birth cohort independent of year of diagnosis. These data are consistent with an environmental cofactor for Kaposi's sarcoma which is likely to be a sexually transmitted agent.

Progression to AIDS and predictors of AIDS in seroprevalent and seroincident cohorts of homosexual men

As part of an ongoing prospective study of seropositive homosexual men in Vancouver, Canada, a seroprevalent cohort of 246 subjects (i.e. duration of infection unknown) and a seroincident cohort of 102 subjects (i.e. duration of infection known) were followed a median of 63 and 45 months, respectively. Follow-up with validation utilizing record linkage with the Canadian Federal Centre for AIDS registry revealed 58 and nine cases of AIDS in the seroprevalent and seroincident cohorts, respectively, through July 1988. These data yield product limit estimates of the cumulative progression rates to AIDS at 60 months of 23.0% for the seroprevalent cohort, 13.0% for the seroincident cohort, and 21.0% for the combined groups. Univariate analyses revealed the following to be statistically and clinically significant predictors of AIDS progression: low CD4 counts, low CD4/CD8 ratios, elevated immune complexes, elevated immunoglobulin G (IgG) and immunoglobulin A (IgA) levels, and low platelet counts. Cox regression revealed that elevated IgA levels, low CD4 counts, elevated immune complexes, two or more symptoms, and more than 20 male sexual partners in high-risk areas in the 5 years prior to enrollment were independent predictors of progression to AIDS over the subsequent 5 years. A multivariate risk function based on the latter five variables delineated low-, medium- and high-risk groups whose 5-year progression rates to AIDS were 6.7, 15.6 and 64.4%, respectively. The high-risk group contained 75% of all subjects who progressed to AIDS. Only 6% of the high-risk group would have qualified for zidovudine therapy under current guidelines at the beginning of the observation period.(ABSTRACT TRUNCATED AT 250 WORDS)