Incidence of human immunodeficiency virus antibody in a prenatal population at a community hospital

Human Immunodeficiency Virus Diagnostic Testing: 30 Years of Evolution

A concern during the early AIDS epidemic was the lack of a test to identify individuals who carried the virus. The first HIV antibody test, developed in 1985, was designed to screen blood products, not to diagnose AIDS. The first-generation assays detected IgG antibody and became positive 6 to 12 weeks postinfection. False-positive results occurred; thus, a two-test algorithm was developed using a Western blot or immunofluorescence test as a confirmatory procedure. The second-generation HIV test added recombinant antigens, and the third-generation HIV tests included IgM detection, reducing the test-negative window to approximately 3 weeks postinfection. Fourth- and fifth-generation HIV assays added p24 antigen detection to the screening assay, reducing the test-negative window to 11 to 14 days. A new algorithm addressed the fourth-generation assay's ability to detect both antibody and antigen and yet not differentiate between them. The fifth-generation HIV assay provides separate antigen and antibody results and will require yet another algorithm. HIV infection may now be detected approximately 2 weeks postexposure, with a reduced number of false-positive results.

High false-positive rate of human immunodeficiency virus rapid serum screening in a predominantly hispanic prenatal population

OBJECTIVE

To identify the characteristics of the gravidas delivering at our birthing center that place them at risk for false-positive human immunodeficiency virus (HIV) enzyme-linked immunosorbent assay (ELISA).

STUDY DESIGN

The medical records of all rapid HIV-ELISA-positive gravidas that delivered at our hospital between January 2000 and October 2001 were retrieved, and information was gathered regarding maternal demographics. The results of the Western blot tests were also retrieved and correlated to the ELISA results, across varying maternal characteristics. chi(2), Student's t-test and multivariate analysis were performed, as appropriate, using the SAS software; statistical significance was denoted by p<0.05.

RESULTS

A total of 69 patients had a positive rapid HIV-ELISA out of 9,781 deliveries. Of those, 26 were confirmed as HIV infected by Western blot (overall HIV prevalence: 0.27%, ELISA-positive predictive value: 37.7%). The subgroup prevalence of HIV and positive predictive value of ELISA were 1.53 and 75% among Caucasians; 2.43 and 82.6% among African-Americans; and 0.05 and 9.8% among Hispanics, respectively (p<0.05 for the comparisons between Hispanics and non-Hispanics only). A history of multiple (> or =5 lifetime) sexual partners was elicited in the majority of HIV-infected patients.

CONCLUSIONS

The positive predictive value of rapid HIV-ELISA during pregnancy varies widely, depending on maternal race/ethnicity and sexual behavior. The routine disclosure of rapid intrapartum HIV serum screening results prior to Western blot confirmation should be avoided in very low-risk populations.