Reports on HIV/AIDS: 1990

NOVEMBER 30, 1990, MMWR, Vol. 39, RR-16 [inclusive page numbers]
tions occurred among adult U.S. residents during 1986-1988, CDC used the results
from this alternative analysis in making projections.
For each year, the plausible range for AIDS case projections (Tables B2 and B3)
consists of the smallest and largest predictions from extrapolation (Hyman; CDC),
from back-calculation without therapy effects fit to adjusted AIDS incidence (through
June 1987 by Rosenberg; June 1989 by Hyman; December 1989 by Hay), and from
Brookmeyer's and Gail's modifications of back-calculation incorporating effects of
improved medical care. These modifications assume 0 to 150,000 new HIV infections
per year since July 1987. Projections obtained from reported cases (Table B2) were
increased by 18% to obtain projections for all diagnosed cases (Table B3), corresponding to the estimate that 85% of all cases diagnosed are eventually reported.
Projections for cases within groups defined by risk behavior, by race/ethnicity, and
by gender were based on projections for all cases and projections for the proportions
of cases within each group. Projections of the proportions of cases in a group were
made by extrapolating the trend in the monthly proportion of cases in that group
(after adjusting for reporting delays) observed for July 1987 through June 1989 (Al ).
The predicted range for each month in the group was then obtained by multiplying
the predicted range for all cases by the predicted proportion for that group. The
annual prediction is the sum of the monthly predictions.
4. Estimation of HIV prevalence from back-calculation estimates of
cumulative HIV incidence
Because back-calculation is based on numbers of reported AIDS cases, this
method estimates cumulative HIV incidence-the total number of persons infected
with HIV in the past-for those persons who have been or will be diagnosed with
AIDS and whose diagnosis will ultimately be reported. This estimate includes persons
diagnosed as having AIDS who have died, but excludes two groups of infected
persons who will never be reported as AIDS cases: a) all diagnosed but unreported
AIDS patients, and b) all those infected with HIV who are never diagnosed as having
AIDS. These patients are never diagnosed as having AIDS because they either have
an unrecognized disease or they die from another cause (e.g., pneumococcal
pneumonia, endocarditis, influenza [A12]) before developing a disease that fits
within the surveillance definition for AIDS.
Estimates of HIV prevalence can be obtained from back-calculation results by
making the corresponding adjustments, i.e, by subtracting deaths associated with
reported AIDS cases and then adjusting the resulting estimate for the number of
persons with HIV infection who will never be reported as having AIDS.
Adjusting for deaths among persons reported as having AIDS. The first step in
estimating HIV prevalence from the back-calculation estimates of cumulative HIV
incidence is to subtract deaths among patients reported to have AIDS. This step gives
an estimate of HIV prevalence for infected persons who will ultimately have a
reported diagnosis of AIDS. The survival analyses described in Section 5 of this
appendix yield estimates of approximately 12,000 deaths for persons diagnosed with
AIDS through 1985; 61,000 through 1988; and 74,000 through June 1989. The last two
estimates are approximately 4% higher than the corresponding numbers of reported
deaths, in part due to reporting delays.

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