Reports on HIV/AIDS: 1990

NOVEMBER 30, 1990, MMWR, Vol. 39, RR-16 [inclusive page numbers]
Adjustment for incomplete ascertainment of life-threatening symptomatic HIV
infection by AIDS surveillance data. If ascertainment of severe HIV infection has not
been constant, a correct estimate of cumulative HIV incidence would require adjusting for under-ascertainment before carrying out back-calculation. Although the
analysis by Buehler et al. (A13) suggests that ascertainment improved in the
mid-1980s, the information on trends in ascertainment is not sufficiently reliable to
adjust reported AIDS cases before applying back-calculation. CDC made the simplifying assumption that ascertainment has been approximately constant and adjusted
the estimates from back-calculation based on AIDS incidence for reported cases to
account for incomplete ascertainment. Because data are not available on the time
from HIV infection to life-threatening symptomatic HIV infection (resulting in death)
among persons who die without meeting the AIDS surveillance definition, CDC also
assumed that this time period has the same distribution as that of the time from HIV
infection to AIDS. On the basis of the results of Buehler et al. (A 13) and the following
analyses,- CDC assumed that reported AIDS cases represent 75% of all severe health
problems associated with HIV infection. Because 1/0.75 = 1.33, CDC estimated HIV
prevalence as 1.33 times the back-calculation estimate of cumulative HIV incidence
minus deaths. Note that this adjustment includes diagnosed but unreported AIDS
cases.
Although definitions of life-threatening symptomatic HIV infection may vary, the
most important measure of such disease not meeting the AIDS surveillance definition
is the extent of HIV-related death. The CDC estimate of ascertainment is based on
comparing surveillance data with vital statistics data. Buehler et al. (A 13) estimated
that, for male U.S. residents 25-44 years of age (the group most affected by the
HIV/AIDS epidemic), at least 70%-90% of the actual number of deaths that occurred in
1987 and were attributable to HIV infection were reported to the CDC AIDS surveillance system. A reasonable estimate, then, is that in 1987 approximately three-fourths
of deaths attributable to HIV infection were reported. Similar analyses indicate that at
least two-thirds of such deaths during 1985-1986 were reported; part of the improvement in reporting from 1985-1986 to 1987 could be due to the expansion of the
surveillance definition in 1987. Preliminary analyses, based on provisional mortality
data, suggest that the proportion of deaths that were attributable to HIV infection and
reported to CDC remained at approximately three-fourths in 1988. These results can
be used to estimate HIV prevalence (by adjusting prevalence estimates obtained from
back-calculation) if nearly all deaths of persons reported to have AIDS are reported to
the surveillance system and if ascertainment is similar for other men and women.
Surveillance data indicate that most deaths are reported of persons whose AIDS
diagnoses had been reported earlier. Among all adults and adolescents with reported
diagnoses, at least 90% of those diagnosed before 1984 have been reported as having
died. Approximately 89% and 87% of those diagnosed as having AIDS in 1984 and
1985, respectively, are also known to have died (A14). The corresponding percentages of male U.S. residents 25-44 years of age at diagnosis and known to have died
are about the same. Reporting of deaths is likely to have improved recently because
many local surveillance units now routinely use death certificates as an adjunct to
both case finding and mortality follow-up. Because these data indicate that at least
90% of deaths associated with reported AIDS cases are reported, an analysis of
ascertainment of life-threatening symptomatic HIV infection based on deaths is
indicative of comparable HIV-associated health problems detected with the CDC AIDS
surveillance system.

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