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Global HIV stats called into question by US study

Global HIV stats called into question by US study

作者:禹畏肥  时间:2019-03-01 07:18:08  人气:

By Andy Coghlan For more than a decade, US health officials have annually been underestimating new HIV infections by 40%. US researchers reporting the discrepancy say that the implications for global HIV figures are unclear, but the World Health Organisation today defended the accuracy of its current estimates. The US underestimate, revealed 3 August at the 17th International AIDS Conference in Mexico City, was exposed by a new blood test that reveals how recently someone has been infected. In the wake of the findings, the US Centers for Disease Control in Atlanta, Georgia, raised its national estimate of the annual infection rate by 40%. This takes the figure to 56,300, from the previous calculation of 40,000. “Our earlier estimate was based on less precise methods,” says Irene Hall, chief of the CDC’s HIV Incidence and Case Surveillance Branch. But Hall said that the CDC had always suspected that 40,000 was an underestimate, based on data from smaller studies monitoring infection trends. She could not say whether estimates elsewhere in the world were also wrong, as “the methods are all different in other countries”. Most countries take the latest data on the national prevalence of HIV, then estimate the number of new cases by applying pre-calculated “correction factors” to the overall numbers. The new national estimate for the US is the first to be based on direct analysis of samples from patients. Called the BED HIV-1 Capture Enzyme Immunoassay, the test reveals the proportion of a person’s antibodies primed to combat HIV. Because anti-HIV antibodies peak weeks after infection then subside, it’s possible to tell how recently someone was infected. Unused blood samples and medical data taken in 2006 from 6864 patients in 22 US states were anonymised, then sent to the CDC for analysis. Of these, 31% turned out to be recent infections, allowing Hall and her colleagues to calculate the new national figure. The data confirmed earlier studies showing that the highest rate of infection is in men who have sex with other men, accounting for 53% of all new infections in 2006. Some 31% were through high-risk heterosexual sex. And, ethnically, black Americans were worst affected, accounting for 45% of all new cases. The most recent global revisions, published in November last year, included drastic downgrades of the numbers of cases, thanks mainly to revised and more optimistic figures from India. “The big change last November was a reduction from 40 million people worldwide living with HIV to 33.2 million,” says Kevin De Cock, director of HIV/AIDS at the WHO. “There was also a reduction in estimates of new infections, from 4 to 5 million down to around 2.5 million per year,” he says. De Cock today defended the accuracy of the global figures. “Do I think the current estimates are good? Yes I do,” he said, adding that they were based on the best figures available in difficult setting. But he said that the US discrepancies were startling, and that “there is a risk that we might sometimes underestimate”. De Cock praised the US surveillance system as the best in the world, but cautioned that few, if any, other countries could afford such sophisticated monitoring. Instead they have to make to with what’s affordable and practical. In many countries, for example, national projections of new infections might be based on data from very small cohorts of high-risk groups, such as men who have sex with men. “But can you be sure your cohort is representative of the total population of men who have sex with men?” he said. Journal reference: Journal of the American Medical Association (vol 300, p520) HIV and AIDS – Learn more about the worst pandemic in human history in our continuously updated special report. More on these topics: