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Amencan Journal of Epidemiology Vol 134. No f
" 5 Copyright r1991 by The Johns Hopkins University School of Hygiene and Public Health Printed in U. S A
All rights reserved
Estimating the 1978-1990 and Future Spread of Human
Immunodeficiency Virus Type 1 in Subgroups of Homosexual
Men
Donald R. Hoover,' Alvaro Munoz,' Vincent Carey,' Joan S. Chmiel,2
Jeremy M. G. Taylor,3 Joseph B. Margolick,' Lawrence Kingsley, and Sten H. Vermunds
The authors studied the historical spread of human immunodeficiency virus type 1
(HIV-1) infection in homosexual/bisexual men and projected its future spread in these
men using data from an AIDS-free cohort recruited during late 1984 in Baltimore.
Maryland; Chicago, Illinois; Los Angeles, California; and Pittsburgh, Pennsylvania. Dates
of preentry seroconversion in HIV-1 seroprevalent men were estimated using study
entry values of hematologic variables influenced by HIV-1 infection. The authors used
survival methods incorporating truncation to determine numbers/dates of seroconver-
sion for men with a pre-1984 AIDS diagnosis who were selectively excluded by design
from the 1984 AIDS-free cohort. Overall, the annual seroconversion hazard rose
progressively from 0.4% in 1978 to 13.8% in 1983, dropped to 4.6% in 1985, and
remained relatively stable at 1.1-2.2% from 1986 to 1990. By January 1990, almost
46% of men who were seronegative in 1978 had seroconverted. The authors estimated
historical rates of spread by city, age, education, and ethnicity to examine the effects
of these factors in the early and continuing stages of the HIV-1 epidemic. There were
striking differences among cities with respect to pre-1985 seroconversion rates but not
with respect to post-1985 seroconversion rates. Age, education, and ethnicity were all
associated with 1978-1990 seroconversion rates. Future seroconversion among ho-
mosexual men was predicted assuming that the 'stabilized" 1986-1990 hazards
(stratified by age) observed here will be representative of future rates. Truncated
Kaplan-Meier methods gave the probability of a seronegative 20-year-old man's remain-
ing seronegative in subsequent years. Such a man has a 20.2% chance of serocon-
verting before reaching the age of 25 yearsi(a4.4% yearly hazard). The annual hazard
drops to 2.5% between 25 and 30 years, to about 1.5% between 30 and 45 years, and
to 1.0% between 45 and 55 years. The overall probability of seroconversion prior to
age 55 years is about 50%, with seroconversion still continuing at and after age 55.
Given that this cohort consists of volunteers receiving extensive anti-HIV-1 transmission
education, the future seroconversion rates of the general homosexual population may
be even higher than those observed here. Am J Epidemiol 1991;134:1190-1205.
acquired immunodeficiency syndrome; cohort studies; HIV seropositivity; homo-
sexuality; statistics
For a disease with a long incubation syndrome (AIDS), knowledge of the histor-
period. such as acquired immunodeficiency ical spread of the infectious agent. humaO
Received for publication July 8, 1991, and in final form
September 12, 1991.
Abbreviations: AIDS, acquired immunodeficiency syn-
drome: HIV-1, human immunodeficiency virus type 1;
MACS. Multicenter AIDS Cohort Study.
' Departments of Epidemiology, Biostatistics, and En-
vironmental Health Sciences, The Johns Hopkins Univer-
sity School of Hygiene and Public Health, Baltimore, MD.
2 Cancer Center Biometry Section, Northwestern Uni-
versity Medical School, Chicago, IL.
3 Department of Biostatistics. UCLA School of PutiC
Health, and Jonsson Comprehensive Cancer Center. LS
Angeles. CA.
'Department of Infectious Diseases and Microbio1'
Graduate School of Public Health. University of Pittsburgh
Pittsburgh, PA.
5 Epidemiology Branch, Division of AIDS, National
tute of Allergy and Infectious Diseases, National Institute
of Health, Bethesda, MD.
MACS centers and investigators: Data Coordinatin4
1190
