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Background:  Diagnosis of HIV infection in infants born to HIV-infected mothers is problematic in many resource-poor countries. Conventional HIV IgG ELISA cannot be used due to presence of passively transferred maternal HIV IgG antibodies and is useful only after 18 months of age. Availability of HIV DNA PCR is limited because of technical and financial constraints. In search of a low-cost diagnostic tool we evaluated HIV-specific IgA assay by ELISA, which is available in most laboratories in India.

Methods:  In this study, vertically exposed infants (n = 150) born to HIV⁺ mothers were recruited:  group I, neonates < 28 days (n =  50); group II, > 28 days to < 18 months (n = 50); group III,  > 18 months (n = 50). Patients in group I were followed prospectively. ELISA was standardized for detection of HIV specific IgA antibodies to HIV-1and -2 antigens in serum after absorption of IgG antibodies. The results of HIV-specific IgA ELISA were compared with HIV DNA PCR and p24 antigen assay. PCR for detection of HIV1 DNA was performed using gag and env primers and LTR-specific nested primers were used for detection of HIV 2. p24 antigen detection was performed with a commercial kit.

Results:  In the 150 children recruited in this study, HIV transmission had occurred in 48% (73 of 150) of children as determined by HIV DNA PCR. HIV 1 was the predominant infection, with only 1 case of HIV2. HIV-specific IgA ELISA was evaluated taking HIV DNA PCR as the gold standard. HIV-specific IgA ELISA was negative in all neonates < 28 days of age. On prospective follow up of these infants, HIV-specific IgA antibody appeared from 3 to 9months of age. In infants < 18 months, the sensitivity of HIV specific ELISA was found to be 71% and specificity was 100%. The sensitivity of p24 antigen ELISA was 42 % and specificity was 100%. In infants > 18 months the test correlated well with the disease severity. HIV specific antibody was found in 31% asymptomatic vs 100% symptomatic cases. Presence of p24 antigen showed 100% concordance with HIV specific IgA antibodies in symptomatic HIV-infected cases of this group.

Conclusions:  HIV specific ELISA can be used for diagnosis of vertically transmitted HIV infection in infants less than 18 months of age in resource poor countries. The presence of HIV-specific antibodies in cases with symptomatic disease could reflect extreme B-cell activation. The utility of this assay as a marker of disease progression needs further investigation.

Keywords: HIV specific IgA ELISA; Vertical HIV infection, Infants,India; Diagnosis & Marker of disease progression.