3 min

Changing tests may cut new HIV cases

BC could be first province to make switch

Researchers at the BC Centre for Disease Control (BCCDC) want to replace the blood test most often used for routine HIV screening in BC with a more expensive but more accurate one that, they say, will help to reduce the spread of the virus.

Today, the most widely used HIV test in Canada is called an enzyme-linked immunosorbent assay (ELISA). But that test does not directly detect the virus that causes AIDS; rather, it identifies the presence of HIV antibodies in the bloodstream produced by the body’s own immune system.

The disadvantage of the ELISA test is that it can take up to six months for HIV antibodies to reach detectible levels. So, a person who is very recently infected may have millions of copies of HIV teeming through his veins, and be at extremely high risk of passing the virus to others, but still test negative for HIV antibodies.

Dr Michael Rekart, Director of Sexually Transmitted Disease and HIV/AIDS Control at the BCCDC, says that detecting new HIV infections as early as possible is critical in reducing prevalence rates.

“Nobody wants to infect anybody else,” he says. “But the earlier in the infection, the higher the likelihood that people are more infectious, and the less likely they are to know about it, or suspect it.”

Rekart says the scientific literature shows that earlier detection means earlier partner notification, counselling and treatment for concurrent sexually transmitted infections. That, in turn, means fewer new HIV infections.

In an effort to detect new HIV cases earlier, Rekart wants BC to switch from ELISA to a test called nucleic acid amplification testing, (NAAT).

“The NAAT will return a positive result within the first week after a person has been exposed to HIV,” he says. “It tests for ribonucleic acid, which is actually part of the virus and there is enough valuable evidence to make switching tests worthwhile in the long term.”

NAAT is not new technology.

“It is widely used in some forms of diagnostics, such as detection of HIV infection in babies born to infected mothers,” explains Dr Paul Sandstrom, Director of National HIV and Retroviral Laboratories at the Public Health Agency of Canada in Ottawa. He says NAAT has been the standard for newborns since about 1993.

Canadian Blood Services has used NAAT to screen every unit of donated blood since 2001, but still refuses to allow any man who has had sex with another man even once in the last 30 years to donate.

So, while NAAT is deemed appropriate for babies and the blood supply, the less accurate ELISA test is still considered good enough for routine testing of general populations, including gay men.

“The Canadian public has zero tolerance for any issues to do with HIV in the blood supply,” says Sandstrom. “They have applied NAAT testing to try to eliminate any potential for transmission, but that comes with an economic cost.”

Rekart does not feel that the health care system is letting gay men down by continuing to use ELISA.

“ELISA is still the standard that’s used across Canada, North America, and the world,” he says. “However, NAAT presents a step forward which is in the early piloting stages for routine testing in a couple of places. It’s not like we’re behind the times.

“General jurisdictional testing of NAAT has only really been used by the state of North Carolina,” he explains. “The results were first published in the New England Journal of Medicine in May of 2005.”

Rekart says the biggest obstacle facing the implementation of routine NAAT testing is cost.

“The NAAT is about $60 and the ELISA is around $10, so the cost differential is six to one,” says Rekart. “The health care system budget is tight and we can’t say NAAT is resource neutral in the short term.”

“One of the questions that needs to be addressed is whether or not the addition of another test, which adds cost, is going to capture a significant number of new infections,” says Sandstrom.

But, regardless of the number of lives impacted, Rekart thinks the initial extra cost is easy to justify.

“Every HIV infection costs the health care system $150,000 to $200,000,” he reasons. “There are also a lot of indirect and social costs, which may raise the price tag to $500,000 per case. So, for every infection you prevent, you’re saving direct health care costs.”

And Rekart says he is making progress toward launching a pilot study of NAAT for BC.

“We presented the idea at the provincial Health Services Authority board meeting, and I’m scheduled to present it to the Ministry of Health early in the new year,” he says. “We’ve been received well. We’ve cobbled together about half of what we need to get started, but we’re lacking about $300,000.

“The ministry is interested in moving forward,” he adds. “It’s a question of getting all the ducks in line, getting the right people to approve it, and then finding the money. Finding the money in our health care system, at this point, where the costs are going up everywhere is not easy.

“The fact that we’re actually considering NAAT and that we have support to a certain degree puts us at the front of the pack,” he says. “I believe that the NAAT will be the standard in a few years. We’re just trying to get there faster than everybody else.”