Superinfection of HIV

Superinfection, despite its super sounding name, is not a good thing. It’s another term for “re-infection” and has been somewhat of a controversial topic in HIV research.

What’s the big deal?

If we have HIV already, getting infected again may not at first glance seem to be such a big deal. Getting diagnosed for the first time is probably harder that getting told that you’ve been infected again.

However, getting infected with a new strain of HIV can have potentially serious effects on our health. For instance, superinfection with a virus that is resistant to antiretroviral drugs could limit future options for what therapies to go on.

Of course, having unprotected sex or sharing needles is the most likely way to get re-infected, and these activities put both us and our partners at risk for not only HIV but also other infections that can affect our health. The best way to cut down on risk (including superinfection) is definitely to use condoms when we’re having sex and to always use clean needles.

How common is superinfection?

A couple things have made me decide to blog about superinfection. First, reader “Teyshan” wanted to know more about it and suggested that I should write a post about superinfection. Second, there was a new study out this week in the Journal of Infectious Diseases that seems to indicate that superinfection is actually quite a rare event.

The paper, published by Rachinger and colleagues, looked at over 100 blood samples taken over time from 15 gay men living with HIV in Amsterdam. All these men were treatment-naïve, meaning they were not currently taking antiretroviral drugs and had not taken any in the past.

The men were studied for around 6 years after first entering the study, and had multiple blood samples drawn over that time. They also answered questionnaires during that time on whether they had been having unprotected sex which would put them at risk for HIV superinfection. These 15 patients were specifically chosen because they had samples taken during periods when they reported risky sexual behaviour. Periods like that are when you’d be most likely to see evidence for superinfection.

How do you look for superinfection?

The researchers looked at two regions of the virus from each sample to increase their chances of detecting superinfection, since it’s possible that the patients could have been reinfected with a virus that was similar to their own virus in one region but not another. Overall, the authors were able to isolate over 1500 sequences of HIV from these patients.

They then used a process called “phylogenetic analysis” to put these sequences into phylogenetic “trees”. These trees tell us how closely related the viruses were to one another. You may have seen trees like this that are used to show how humans are related to other species of monkeys and primates. If one of the viruses from a patient were too different from the other viruses that had previously been seen in that patient, then that virus would sit at the end of a longer “branch” compared to the others in the tree. An extra long branch could possibly indicate superinfection with a different virus.

However, of the more than 1500 sequences they looked at from these men, taken from many years while living with HIV, not one patient showed any evidence of superinfection.

Rare, but serious

This rarity of superinfection is echoed in other studies. One large study which followed almost 40 patients for a number of years also found no evidence of superinfection. There have only been around 15 confirmed cases of HIV superinfection in humans.

Generally, these cases have been within the first year after getting initially infected with HIV, with superinfection being rarer after someone has lived with HIV for longer. It is possible that once the immune system has had time to adapt to someone’s HIV that this immune response – even though it isn’t enough to clear the HIV infection from the body – may help protect against getting reinfected with HIV.

Despite the fact that superinfection is somewhat rare, the consequences of superinfection can be very serious. For example, there has been one case of superinfection of an elite controller. This patient had been able to control his virus for at least 12 months without needing therapy, but after having unprotected sex with an HIV infected partner, he was infected with another strain of HIV. Although previously having an undetectable viral load, this patient ended up having a much higher viral load after the superinfection, that his immune system could now not control as well.

Most cases of superinfection have resulted in higher HIV viral loads and lower CD4 cell counts in patients after infection, suggesting that superinfection can lead to worse outcomes in HIV disease.

There have also been cases of a superinfection with a drug resistant virus. This limits which drugs someone can go on to later when they need treatment.

The message

To sum up, although HIV superinfection seems to be a fairly rare event, the consequences can be serious, including limiting treatment options and making HIV disease worse. The best way to protect against superinfection (and transmission of HIV to others) is to practice safe sex and use clean needles.

A lot of messages get thrown at people living with HIV. Of course, doctors encourage positive people to have safe sex as much as possible. But there are also messages about how going on treatment also reduces the risk of passing on HIV to others. Some doctors and researchers also encourage “serosorting”, where positive people are encouraged to have sex with other positive people instead of people who are negative, in order to reduce further transmission. Yet there is also messaging about how serosorting with other positive people can lead to superinfection. All these messages can lead to serious confusion about how to make the healthiest choices.

YouthCO believes that giving people all the facts enables them to make their own decisions on how best to keep themselves healthy.