Untreated carriers transmit resistant HIV

Swiss researchers solve another piece of the HIV transmission puzzle Keystone/NIAID

Researchers of the Swiss HIV Cohort Study have shown that the majority of resistant viruses are transmitted by untreated people and not, as previously thought, by carriers whose viruses had built up drug resistance during therapy.

The authors of an article in the medical journal Clinical Infectious Diseases concluded that physicians who treat infections caused by the human-immunodeficiency virus (HIV) should focus on diagnosing new infections early to better prevent transmission by people who are not yet undergoing treatment.

People who are diagnosed with HIV in Switzerland stand a very good chance of never getting ill. More than 90% of patients successfully respond to existing therapy, which is designed to suppress the virus and stop disease progression.

The main challenge today is that many carriers unknowingly transmit potentially resistant viruses for years, said researcher Roger Kouyos from the Zurich University Hospital. Many infections are not discovered until much later than they could and should have been, he said.

“Once you have a problem with drug resistance, it can often be too late because resistance persists and doesn’t just go away if carriers don’t undergo treatment,” Kouyos explained. “The problem is that untreated carriers can therefore pass on resistant viruses for years before they’re diagnosed and treated.”

HIV in Switzerland

Compared with other western European countries, Switzerland has a relatively high prevalence of HIV/AIDS among the general population – around 0.4% of people are carriers of HIV.

HIV infection rates among homosexual men, migrants from sub-Saharan Africa, and drug users are around 5%.

More than 32,000 positive HIV tests have been reported since records began, currently there are around 25,000 people living with HIV/AIDS.

In 2012, 620 new HIV diagnoses were reported; women accounted for 25%. About 44% of all infections result from heterosexual contact.

Since 1983, almost 6,000 people have died as a result of AIDS.

Drug resistance

Around one in every ten newly infected people in Switzerland carries viruses that no longer respond to at least one of the three classes of antiretroviral AIDS drugs. The good news is that there are still quite a few effective treatment alternatives once a resistance is detected.

But a lot still needs to be done. As therapy today is close to optimal, physicians can make the main difference if they diagnose and treat the disease earlier, so that they more successfully break the transmission chain, Kouyos said.

The researchers led by Kouyos and Huldrych Günthard from the Zurich University Hospital looked at data from 1,674 homosexual male carriers of HIV at Swiss specialist clinics to better understand how resistant viruses were transmitted. They identified resistant viruses in 140 patients.

When they reconstructed the transmission chains on the basis of the patients’ estimated infection dates and the genetic relations of their viruses, they found that most of the resistant HIVs were transmitted in carriers who were not yet undergoing treatment at the time.

Astonishing finding

“We were astonished to note that the resistant viruses are primarily brought into circulation by untreated people,” said Günthard. “Previously we had assumed that the resistant viruses came from patients for whom treatment had failed as resistances were produced while treatment was ongoing.”

One of the goals of therapy should be early detection, but HIV remains more stigmatised than other infectious diseases, Kouyos said. Doctors are still reluctant to discuss their patients’ sexuality with them openly and unlike tests for hepatitis, HIV screenings require the patients’ permission.

The Swiss National Science Foundation (SNSF) funds the Swiss HIV Cohort Study, which started in 1988 and whose aim is to better understand HIV infection and AIDS. Currently,  more than 8,800 people are taking part; almost one third are women.