Quantitation of human immunodeficiency virus in vertically infected infants and children.

We used a quantitative human immunodeficiency virus, type 1 (HIV-1) culture method to determine whether there is a relationship between the amount of replicating virus in the blood of vertically infected children and the relatively short latency period before development of symptomatic disease in these children. HIV-1 titers were determined by end point dilution in the peripheral blood mononuclear cells and the plasma of 30 infected (CDC class P1 and P2), 36 indeterminate (CDC class PO), and 19 uninfected (CDC class P3) infants and children born to HIV-1 seropositive mothers. HIV-1 was recovered from 35 (90%) of 39 PBMC cultures and 23 (60%) of 38 plasma cultures of infected patients not receiving antiretroviral therapy. The mean HIV-1 titers tended to be higher in patients with more advanced disease (P2, D, E, or F: 1760 TCID/10(6) PBMC, 460 TCID/ml plasma) than in asymptomatic or mildly symptomatic patients (P1; P2, A or C: 90 TCID/10(6) PBMC; 60 TCID/ml plasma). A poor correlation between HIV-1 titers and serum p24 antigen levels was found. No correlation was observed between viral titers and relative or absolute numbers of CD4 lymphocytes. Plasma virus titers were lower in 9 patients receiving zidovudine (ZDV) therapy (mean 2 TCID/ml) than in untreated patients of similar clinical status. The viral titers measured in the blood of vertically infected infants and children were on the same order of magnitude as the viral titers measured in HIV-infected adults. We conclude that the relatively rapid progression to symptomatic disease of the majority of vertically infected patients is not due to a higher load of replicating virus in blood.