Early diagnosis of HIV-1 infection in infants in Dar es Salaam, Tanzania.

Objectives: To evaluate two simple methods, an immune complex dissociation (ICD) p24 antigen assay and an HIV-1-specific IgA antibody assay, for the early demonstration of HIV-1 infection in infants, using the polymerase chain reaction (PCR) as the reference method.

Design And Setting: Group A: 143 HIV-1-seropositive and 134 -seronegative mothers and their infants were recruited at delivery at the main hospital in Dar es Salaam, Tanzania. Group B: 26 HIV-PCR-positive hospitalized children in Dar es Salaam, 3-15 months old and suspected of having an HIV-related illness.

Methods: Blood samples were taken from mothers and infants in group A at intervals during the children's first 24 months and once from each of the children in group B. Peripheral blood mononuclear cells were tested by nested PCR for viral DNA. Plasma samples were tested by the Coulter p24 antigen (ag) enzyme-linked immunosorbent assay (ELISA) after acid dissociation of p24 antigen-antibody complexes. All p24-ag-positive reactions were confirmed by neutralization. Viral specific IgA antibodies were demonstrated in plasma by a modified ELISA.

Results: One hundred and sixty-three of 174 samples from seropositive mothers were PCR-positive (sensitivity 93.7%) and 612 of 614 samples from seronegative mothers and children of seronegative mothers were PCR-negative (specificity 99.7%). Twenty-nine of 145 (20.0%) children born to seropositive mothers were positive by PCR when tested during the first year of life. By use of both the p24 ag ELISA and the IgA antibody ELISA in combination, HIV-1 infection was detected in 9 of 17 (53%) PCR-positive children 1-8 weeks old, in 15 of 18 (83%) PCR-positive children 9-26 weeks old and in 23 of 24 (96%) PCR-positive children 27-52 weeks old. The specificities of the p24 ag ELISA and the IgA ELISA were 100%.

Conclusions: The p24 ag assay and the IgA antibody ELISA, when used in combination, had a high sensitivity and specificity for detection of HIV-1 infection in infants, especially in those above the age of 6 months.