Extent of undiagnosed HIV infection in hospitalized patients: assessment by linkage of seroprevalence and surveillance methods.

Routine screening of hospitalized patients for human immunodeficiency virus (HIV) infection has been suggested as a method to identify undiagnosed HIV infection. To evaluate HIV seroprevalence and rates and risk factors for undiagnosed HIV infection among inpatients at an urban hospital, we linked a blinded HIV seroprevalence survey with data from a health care systemwide HIV surveillance registry. Consecutive nonobstetric adult inpatients admitted over four months had remnant samples of serum and plasma obtained and demographic and clinical data abstracted from hospital registration and outpatient encounter billing files. After linkage with the HIV registry, patient data were assigned a study code, individual identifiers were removed, and specimens were tested for HIV-1 antibody. Of 2,825 eligible patients, 155 (5.5%) were HIV-seropositive: 139 (90%) with known infection and 16 (10%) with previously undiagnosed infection. Of those with previously undiagnosed infection, eight (5%) were newly diagnosed during hospitalization and eight (5%) remained undetected following hospitalization. For HIV-seropositive patients, previously undiagnosed infection was significantly more common among those with no use of the health care system in the past year than those with recent outpatient or inpatient visits (41.7% versus 4.6%, odds ratio [OR] = 14.9, 95% confidence intervals [CI] = 4.7, 47.1). Despite a relatively high hospital HIV seroprevalence, the rate of undiagnosed infection was low, suggesting that the percentage of the HIV epidemic remaining "undetected" may be smaller in some settings than suggested by previous studies of hospitalized patients. Linkage of surveillance data to blinded seroprevalence studies can be of value in estimating this "undetected" percentage and in evaluating the potential yield of routine HIV testing programs. Medical Subject Headings (MeSH): HIV infection, risk factors, HIV seroprevalence, inpatients, HIV screening, population surveillance.