Reports on HIV/AIDS: 1990

NOVEMBER 30, 1990, MMWR, Vol. 39, RR-16 [inclusive page numbers]
described above, as well as the proportion of cases in each group (i.e., IVDUs,
children) assumed to have less complete ascertainment. Assuming arbitrarily that
ascertainment is 50% for IVDUs and children and 80% for other HIV-infected persons,
the level of ascertainment for male U.S. residents 25-44 years of age at diagnosis
would be estimated as 75%. Because this estimate is nearly the same as that of
Buehler et al. (A13), the assumptions of 50% and 80% ascertainment in the two
groups are plausible. Because overall ascertainment is also very close to 75%, it is
reasonable to apply the estimate of 75% ascertainment to all persons infected with
HIV, as was proposed in the adjustment method.
5. Survival after a diagnosis of AIDS
Using the Kaplan-Meier procedure and AIDS surveillance data, CDC estimated
survival after a diagnosis of AIDS. Follow-up time was censored at the end of 1988 to
allow most deaths that had occurred in 1988 to be reported. (Analyses of deaths from
October 1987 to September 1990 indicate that <85% of deaths are reported within 1
year of death.) The resulting survival estimates were used to predict future deaths
among persons diagnosed with AIDS, numbers of persons alive with AIDS, and
deaths associated with symptomatic HIV infection (Tables 2, B2, and B3), and to
estimate HIV prevalence (Section 4).
The AIDS surveillance data show that 13% of persons reported to have AIDS die in
the same month as the diagnosis of AIDS was made; an unknown proportion of these
persons represent late diagnoses of AIDS (perhaps even at death) rather than rapid
progression of disease. Survival patterns associated with the other 87% of AIDS cases
diagnosed in the period 1984 through the first half of 1987 seem to follow an
exponential distribution for the first 24 months after diagnosis, with the risk of death
depending on the date of diagnosis. For persons diagnosed as having AIDS in 1984 or
1985, approximately 45% survived at least 12 months and 50% survived at least 11
months; for those whose AIDS was diagnosed in the period 1986 through the first half
of 1987, 55% survived at least 12 months and 50% survived at least 14 months.
Survival >24 months after diagnosis among these persons appears to be better than
that predicted by an exponential distribution, in part due to delays in reporting deaths
and to deaths never reported. Improved survival among persons diagnosed with
AIDS in 1986 and 1987, compared with the survival period for persons whose AIDS
was diagnosed in earlier years, has also been found in San Francisco (A15) and in
another analysis of national AIDS surveillance data (A 16), especially for patients with
P. carinii pneumonia.
Because there are limited data on survival for persons whose AIDS has been
diagnosed since mid-1987, CDC estimated survival for these persons by modifying
death rates for persons diagnosed as having AIDS from January 1986 through June
1987. The modification was based on the study in San Francisco (A15), which found
that patients taking zidovudine survived longer after a diagnosis of AIDS than patients
not on antiviral therapy (median survival, 21 vs. 14 months; 1-year survival, 85% vs.
56%). Under an assumption of exponential survival, these median survival times
imply a reduction in mortality risk of 35% for patients taking zidovudine.
The number of persons who die each year after being diagnosed as having AIDS
was estimated by applying the estimated survival distribution both to the adjusted
AIDS incidence through June 1989 and to the range of predicted AIDS incidence from
July 1989 through December 1993 (Table 2). The assumption was that 13% of persons

171