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Abstract
Differentiating individuals with early human immunodeficiency virus 1 (HIV-1) infection
from those infected for longer periods is difficult but important for estimating HIV
incidence and for purposes of clinical care and prevention.
To develop and validate a serologic testing algorithm in which HIV-1-positive persons
with reactive test results on a sensitive HIV-1 enzyme immunoassay (EIA) but nonreactive
results on a less sensitive (LS) EIA are identified as having early infection.
Diagnostic test and testing strategy development, validation, and application. Specimens
were tested with both a sensitive HIV-1 EIA (3A11 assay) and a less sensitive modification
of the same EIA (3A11-LS assay).
For assay development: 104 persons seroconverting to HIV-1 comprising 38 plasma donors,
18 patients of a sexually transmitted disease clinic in Trinidad, and 48 participants
in the San Francisco Men's Health Study (SFMHS); 268 men without the acquired immunodeficiency
syndrome (AIDS) in the SFMHS who had been infected for at least 2.5 years; and 207
persons with clinical AIDS; for testing strategy validation: 488 men in the SFMHS
from 1985 through 1990 and 1275449 repeat blood donors at 3 American Red Cross blood
centers from 1993 through 1995; and for HIV-1 incidence estimates: 2717910 first-time
blood donors. We retrospectively identified persons eligible for a study of early
infection.
Ability to identify early HIV infection.
Estimated mean time from being 3A11 reactive/3A11-LS nonreactive to being 3A11 reactive/3A11-LS
reactive was 129 days (95% confidence interval [CI], 109-149 days) [corrected]. Our
testing strategy accurately diagnosed 95% of persons with early infection; however,
0.4% (1/268) of men with established infection and 2% (5/207) of persons with late-stage
AIDS were misdiagnosed as having early HIV-1 infection. Average yearly incidence estimates
in SFMHS subjects were 1.5% per year vs observed average incidence of 1.4 per 100
person-years. Incidence in repeat blood donors using the sensitive/less sensitive
assay testing strategy was 2.95 per 100000 per year (95% CI, 1.14-6.53/100000) vs
observed incidence of 2.60 per 100000 person-years (95% CI, 1.49-4.21/100000). Overall
incidence in first-time blood donors was 7.18 per 100000 per year (95% CI, 4.51-11.20/100000)
and did not change statistically significantly between 1993 and 1996. Use of the sensitive/less
sensitive testing strategy alone would have identified all 17 persons with antibodies
to HIV-1 eligible for a study of early HIV-1 infection and would have increased enrollment.
The sensitive/less sensitive testing strategy provides accurate diagnosis of early
HIV-1 infection, provides accurate estimates of HIV-1 incidence, can facilitate clinical
studies of early HIV-1 infection, and provides information on HIV-1 infection duration
for care planning.