Gaby Vercauteren

Beyond detuning: 10 years of progress and new challenges in the development and application of assays for HIV incidence estimation.

In the ongoing battle against HIV/AIDS, it is critical that we are able to measure and monitor HIV incidence, that is the number of new infections during a period of time, usually expressed as number of infections/person-years of observation or as an annual percentage of the population that acquire infection. Knowledge of HIV incidence is necessary to understand transmission patterns; to provide a rational basis for targeting prevention efforts; to evaluate interventions to reduce transmission; and to predict or project the burden of HIV infection in different demographic and risk populations. Reliable information on HIV incidence is especially important to support prevention programs in the low-income and middleincome countries that continue to bear a disproportionate share of the global burden of the HIVepidemic. Improved estimates of HIV incidence are essential to evaluate

Impact of maternal HIV infection on obstetrical and early neonatal outcome

In a case-control study of 177 HIV-seropositive and 326 seronegative women and their newborns in Nairobi, Kenya, maternal HIV infection at term was independently associated with travel to other African countries [odds ratio (OR) 4.9, P less than 0.0001], history of a blood transfusion since 1980 (OR 3.5, P = 0.01), history of more than one sexual partner in the previous 5 years (OR 1.8, P = 0.02) and unmarried status (OR 1.8, P = 0.02). Neonates of HIV-positive and HIV-negative women differed little with respect to occurrence of congenital malformations, stillbirths, in-hospital mortality, sex, APGAR score, or gestational age. However, the mean birth weight of singleton neonates of HIV-positive women was significantly lower than that of controls (3090 versus 3220 g, P = 0.005), and birth weight was less than 2500 g in 9% of cases and 3% of controls (OR 3.0, P = 0.007). Among neonates of HIV-seropositive women, birth weight was less than 2500 g in 17% if mothers were symptomatic and 6% if mothers were asymptomatic (OR 3.4, P = 0.08).

EVALUATION OF A CLINICAL CASE-DEFINITION OF ACQUIRED IMMUNODEFICIENCY SYNDROME IN AFRICA

A provisional clinical case-definition for acquired immunodeficiency syndrome (AIDS) developed by the World Health Organisation (WHO) for use in Africa was tested on 174 inpatients at Mama Yemo Hospital, Kinshasa, Zaire. In this hospital population with a 34% infection rate of human immunodeficiency virus (HIV), the clinical case-definition had a specificity of 90%, a sensitivity of 59%, and a predictive value of 74% for HIV seropositivity. These results support the use of the WHO clinical definition for AIDS in Africa. However, since HIV prevalence and disease expression vary, similar evaluations should be carried out in different regions.

Evaluation of a line immunoassay for simultaneous confirmation of antibodies to HIV-1 and HIV-2

An anti-HIV-1/HIV-2 line immunoassay (LIA), using peptides and recombinant antigens was evaluated against commercially available Western blot tests for HIV-1 and HIV-2 antibodies. Two thousand one hundred and ten sera of European, African, and South American origin were used in the evaluation. The panel included 1066 sera with antibodies to HIV-1, 192 sera with antibodies to HIV-2, and 64 sera with antibodies to both. Using Western blot results interpreted according to the WHO criteria as a reference standard, the overall specificity obtained by this LIA was 100 % and the sensitivity was 99.77 % (97.51-100 % for 95 % confidence limits) when sera dually reactive in Western blot were included. Of the three sera negative in the LIA but positive in HIV-1 WB, two could be retested in a radioimmunoprecipitation assay and were negative. When dually reactive sera in the Western blot (WHO) were included, the LIA yielded 9.9 % indeterminate results as compared with 15.5 % for both assays (x2=29.30; p<0.001). Although only one HIV-2 specific peptide antigen (gp36) was used, the LIA yielded a specificity of 100 % and a sensitivity of 100 % as compared with the HIV-2 Western blot assay. When indeterminate results were included, the overall agreement between the LIA and the HIV-1 and HIV-2 Western blot (WHO criteria) was 89.9 % and 90.1 % respectively. These results indicate that the LIA provides reliable simultaneous detection of antibodies to HIV-1 and HIV-2, and at a cost which is substantially lower than the cost of Western blot tests.

Immunofluorescence tests for HIV antibody and their value as confirmatory tests

The enzyme-linked immunosorbent assay (ELISA) is currently being used as a sensitive screening test for HIV antibody. The immunoblot assay (IBA) and indirect immunofluorescence (IF) techniques are two recommended confirmation tests for EIA-positive sera. An indirect IF test has been developed by various laboratories using acetone fixed mixtures of uninfected and HIV-infected cells, which facilitated the reading, since nonspecific reactions were easily differentiated from specific staining. Similar results have been obtained with H9-, CEM-, and HUT78-HIV-infected and uninfected cells. Anti-nuclear antibodies and auto-antibodies resulting in false-positive EIA results, could easily be differentiated by the IF test. Aspecific fluorescence can be removed by absorption of the specimens with non-infected cells. However, IF is not suitable for the screening of large series of specimens. IF is especially well suited for quantitative analysis of serum antibody levels. Whereas serum antibody titers rise initially after infection, they decrease as AIDS develops. Heat inactivation of sera did not affect reactivity in IF, in contrast to a high rate of false-positive results obtained with heat inactivated sera in some ELISAs. A well characterized serum from an AIDS patient can be used to perform IF in order to monitor HIV infection of susceptible cells. It has been claimed that titers of neutralizing antibodies significantly correlate with the levels of IF anti-HIV antibodies. An overall correlation of 99% between IF and IBA was reported by different laboratories, when HIV ELISA-reactive European and North American sera were tested. The concordance with IBA was 97% when HIV ELISA-reactive African sera were tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of an agglutination HIV-1 + 2 antibody assay

Studies have shown that an HIV (HIV-PA) agglutination assay (Serodia) for the detection of antibody to human immunodeficiency virus (HIV) can be as sensitive and as specific as enzyme-linked immunosorbent assay (ELISA). However, since this HIV assay was designed to detect antibody to the HIV-1 virus, a substantial number of HIV-2 positive sera are missed by this assay. Since the HIV-2 has now been found throughout the world this test is becoming less suitable. The new HIV-1 + 2 assay version (HIV-1 + 2 PA) was evaluated in 300 sera, which contained 50 HIV-1, 40 HIV-2 and 10 HIV-1/HIV-2 antibody positive samples, and a sensitivity and specificity of 100% and 99%, respectively, was obtained. Whereas all HIV-2 positive sera were detected by the new HIV-1 + 2 version, 26% (13/50) were missed by the old version of the agglutination test. It is concluded that the HIV-1 + 2 PA assay is a promising instrument free assay which can be used for screening purposes in areas where both HIV-1 and HIV-2 are present.

Comparison of enzyme immunoassays and an immunofluorescence test for detection of antibody to human immunodeficiency virus in African sera

A total of 152 sera from African subjects were tested for presence of antibody to human immunodeficiency virus using four enzyme immunoassays (EIA) marketed by Abbott Diagnostics, Organon Teknika, Wellcome and Diagnostics Pasteur respectively, an indirect immunofluorescence assay (IFA) and an immunoblot assay (IBA) as reference test. The sensitivity (95 % confidence limits, CL) of the EIAs and the IFA ranged between 80.9 % and 99.1 %. The specificity of the Abbott EIA was lower (95 % CL: 38.1–72 %) than that of the other assays (95 % CL: 83.5–100 %). The use of an IFA or the Wellcome competitive EIA as confirmatory test on initially EIA positive sera yielded a specificity of 85.5–100% (95 % CL) compared with the IBA. The costs of screening by an EIA, followed by confirmatory testing of reactive sera with IFA or the Wellcome EIA and IBA on discrepant test results was similar for all combinations with the exception of initial screening with the Abbott EIA which was more expensive. Using a limited number of sera from African subjects no one test system yielded a significantly superior degree of specificity or sensitivity.

Evaluation of two enzyme immunoassays for detection of human immunodeficiency virus antigen in African and European sera

The performance of two HIV antigen enzyme immunoassays (EIAs), the HTLV-III antigen EIA (Abbott) and the Innotest HIV antigen EIA (Innogenetics), was assessed using 276 HIV-1 antibody positive and 42 HIV antibody negative sera from European and African individuals. On the initial screening 16 % (51/318) of the sera were reactive in the Abbott EIA and 21.4 % (68/318) in the Innotest EIA. The Innotest detected significantly more confirmed HIV antigen positive sera (55/58, 94.6 %) than the Abbott EIA (41/58, 70.7 %). The presence of free detectable HIV antigen in African and European sera was strongly associated with the clinical classification CDC IV and with low p24 antibody levels.