Ask the Experts - Antibody-Positive Yet HIV RNA-Negative Child?
Ask the Experts - Antibody-Positive Yet HIV RNA-Negative Child?
I am responsible for the care of HIV-infected and exposed children at my hospital in Curicica, Rio de Janeiro, Brazil. We have about 70 infected children. I care for an 11-year-old girl who was diagnosed at the age of 7 by 2 positive ELISAs plus Western blot methods. She has no symptoms and her plasma HIV-1 RNA level is less than 80 copies/mL (our limit of detection) without any treatment. Should it be recommended to perform an HIV DNA PCR in order to confirm infection? This procedure is not available in our public hospitals. I would also like to know your experience with related cases.
In general, we prefer to use HIV DNA PCR (polymerase chain reaction) for the diagnosis of HIV infection in children in whom the presence of maternal antibody might hamper an accurate diagnosis. Early studies demonstrated that 75% of children will lose maternal antibody by 12 months of age and 90% by 15 months; by 18 months only 2% still have evidence of maternal antibody. Thus, as in adults, the presence of HIV antibodies detected after 18 months of age is highly sensitive and specific to establish HIV diagnosis. In the United States the current recommendation for adults and children older than 18 months is to perform the enzyme-linked immunoassay (ELISA) as the initial screening test. If the ELISA is repeatedly positive a Western blot test is performed. The patient is considered to be HIV-infected if there are antibodies to at least 2 of the 3 major core and envelope proteins. Immunofluorescence assay is an acceptable alternative test.
The HIV DNA PCR test is currently the method of choice for the early diagnosis of HIV infection in infants aged younger than 18 months. HIV RNA PCR has been shown to be equally sensitive; however, false-positive results have been detected (specificity, 95%) in infants aged less than 1 month and thus it is probably not wise to use this test exclusively. Prophylaxis with zidovudine does not affect the HIV DNA or RNA PCR results.
Your patient is interesting in that she has been found to be antibody-positive yet HIV RNA-negative. I assume that you have performed CD4+ cell counts and other tests such as quantitative immunoglobulins, which can give you indirect evidence of HIV infection. I also assume that these CD4+ cell counts are normal, that the child has normal height, normal weight, and no clinical symptoms, and that the parent is clinically well and has never had an AIDS-associated illness and does not fit in any category except N1 (ie, asymptomatic, normal CD4+ cell count) of the CDC classification system. If all of this is true then there are several possible explanations. First and perhaps most important is laboratory error. We have documented several occasions when a laboratory reported a positive ELISA with Western blot which was not confirmed in our laboratory. For this reason we always confirm a first result with a second test. If your patient was repeatedly positive on Western blot on 2 separate occasions, then we can be confident that she is indeed HIV-infected.
Her low HIV RNA level may have 2 possible explanations. First, she may be a long-term nonprogressor, as has been well described in adults. These are rarer but certainly not unknown among children. These patients have undetectable HIV RNA levels and a relatively intact immune system. Data both in adults and children have demonstrated that some of these patients have deletions in the HIV nef gene, apparently rendering the virus less pathogenic.
An alternative possibility is that your patient may be infected with an HIV subtype that the Roche PCR assay does not detect. You are located in South America, where epidemiologic evidence indicates that 77% of isolates are subtype B, 23% are subtype F, and less than 1% are A and C. The first-generation Roche RNA and DNA PCR tests are both less sensitive in detecting RNA in patients infected with non-B subtypes; thus, if your laboratory is using these tests you may have a false-negative result. The newer version of the Roche assay, with modification of primers but using the same probes, is more sensitive in detecting non-clade B subtypes.
I am responsible for the care of HIV-infected and exposed children at my hospital in Curicica, Rio de Janeiro, Brazil. We have about 70 infected children. I care for an 11-year-old girl who was diagnosed at the age of 7 by 2 positive ELISAs plus Western blot methods. She has no symptoms and her plasma HIV-1 RNA level is less than 80 copies/mL (our limit of detection) without any treatment. Should it be recommended to perform an HIV DNA PCR in order to confirm infection? This procedure is not available in our public hospitals. I would also like to know your experience with related cases.
In general, we prefer to use HIV DNA PCR (polymerase chain reaction) for the diagnosis of HIV infection in children in whom the presence of maternal antibody might hamper an accurate diagnosis. Early studies demonstrated that 75% of children will lose maternal antibody by 12 months of age and 90% by 15 months; by 18 months only 2% still have evidence of maternal antibody. Thus, as in adults, the presence of HIV antibodies detected after 18 months of age is highly sensitive and specific to establish HIV diagnosis. In the United States the current recommendation for adults and children older than 18 months is to perform the enzyme-linked immunoassay (ELISA) as the initial screening test. If the ELISA is repeatedly positive a Western blot test is performed. The patient is considered to be HIV-infected if there are antibodies to at least 2 of the 3 major core and envelope proteins. Immunofluorescence assay is an acceptable alternative test.
The HIV DNA PCR test is currently the method of choice for the early diagnosis of HIV infection in infants aged younger than 18 months. HIV RNA PCR has been shown to be equally sensitive; however, false-positive results have been detected (specificity, 95%) in infants aged less than 1 month and thus it is probably not wise to use this test exclusively. Prophylaxis with zidovudine does not affect the HIV DNA or RNA PCR results.
Your patient is interesting in that she has been found to be antibody-positive yet HIV RNA-negative. I assume that you have performed CD4+ cell counts and other tests such as quantitative immunoglobulins, which can give you indirect evidence of HIV infection. I also assume that these CD4+ cell counts are normal, that the child has normal height, normal weight, and no clinical symptoms, and that the parent is clinically well and has never had an AIDS-associated illness and does not fit in any category except N1 (ie, asymptomatic, normal CD4+ cell count) of the CDC classification system. If all of this is true then there are several possible explanations. First and perhaps most important is laboratory error. We have documented several occasions when a laboratory reported a positive ELISA with Western blot which was not confirmed in our laboratory. For this reason we always confirm a first result with a second test. If your patient was repeatedly positive on Western blot on 2 separate occasions, then we can be confident that she is indeed HIV-infected.
Her low HIV RNA level may have 2 possible explanations. First, she may be a long-term nonprogressor, as has been well described in adults. These are rarer but certainly not unknown among children. These patients have undetectable HIV RNA levels and a relatively intact immune system. Data both in adults and children have demonstrated that some of these patients have deletions in the HIV nef gene, apparently rendering the virus less pathogenic.
An alternative possibility is that your patient may be infected with an HIV subtype that the Roche PCR assay does not detect. You are located in South America, where epidemiologic evidence indicates that 77% of isolates are subtype B, 23% are subtype F, and less than 1% are A and C. The first-generation Roche RNA and DNA PCR tests are both less sensitive in detecting RNA in patients infected with non-B subtypes; thus, if your laboratory is using these tests you may have a false-negative result. The newer version of the Roche assay, with modification of primers but using the same probes, is more sensitive in detecting non-clade B subtypes.
Source...