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Early infant diagnosis for HIV: is it taking place early enough?
Theo Smart, 2012-03-13 17:20:00
Current early infant diagnosis (EID) protocols may need to be revised in the light of current WHO guidelines on the prevention and treatment of HIV-infection in low-resourced settings, according to Dr. Gayle Sherman of Wits University, South Africa, and senior specialist in Paediatric Haematology with the country's National Health Laboratory Services, speaking at the 19th Conference on Retroviruses and Opportunistic Infections held last week in Seattle.
Dr Sherman described the dramatic advances that have been made in the field over the last several years, but noted that advances in both technology and guidelines have presented new challenges.
“Six weeks may not be the right time to be testing,” she said, referring to the current protocol for performing EID at the six week immunisation visit. Tetsing at this time, she went on, delivers diagnoses a bit too late to take full advantage of lifesaving early antiretroviral therapy (ART) for infected infants, and does not account for the effects that prolonged daily nevirapine prophylaxis could have on diagnostic accuracy (see below).
“We’ve come a very long way in a very short space of time but it’s very difficult to complete a journey when we keep changing the maps: in the forms of technologies and guidelines,” Dr Sherman said.
From serial antibody screening to large-scale PCR tests in less than a decade
HIV-exposed infants carry their mother’s antibodies to the virus for months after childbirth or after their last exposure via breast milk, so standard HIV tests (ELISA tests that look for HIV-antibodies) cannot be used to make a positive HIV diagnosis in young infants. However, HIV antibody tests can be useful for detecting if an infant has been exposed to HIV or to show if an infant is HIV-negative, or if an infant who previously had antibodies seroreverts — in other words, loses those antibodies, when the HIV tests are repeated serially in infants.
If antibodies persist well beyond the last exposure, a positive diagnosis can also be made, typically around the time of 18 months. Since many HIV-infected children don’t survive to this point without treatment, as demonstrated by the CHER study, final results of which were presented on Tuesday at the conference, in 2004, WHO began recommending PCR testing to make an earlier diagnosis in children.
At the time, prevention of HIV transmission to infants was very different. With single-dose nevirapine (sdNVP) having recently been introduced, the preferred feeding option for infants was exclusive formula feeding, and there was no ART available for treatment in low-resourced settings. WHO’s EID diagnostic guidelines for LRS therefore recommended performing a single HIV PCR test at six weeks of age because it was believed that an HIV PCR test at that time would detect virtually all in-utero and intrapartum infections; and because six weeks happened to coincide with an established immunisation visit.
“For the next couple of years, we frantically spent our energies scaling up early infant diagnosis – both in the clinic and in the laboratory. We developed job-aids to explain to nurses how to take blood on babies for a test they’d never heard of; and we crammed our laboratories full of instruments to deliver these tests,” said Dr Sherman. She added that in South Africa, the laboratory services went from performing a couple of thousand PCR tests per year to doing more than 275,000 tests by 2010.
However, there were disparities between, and within, countries. PCR laboratories had varying capacities with turn-around times anywhere between a couple of days to a couple of months of testing. To this day, there are areas where children have to rely on a WHO presumptive diagnosis, rather than a PCR test result, to access ART. Even where PCR laboratories were functioning well, large numbers of exposed infants were not getting into be tested. Finally, many of “those that were getting PCR-positive tests weren’t getting on to treatment,” she said.
Source:1
