Question

Resistance tests accuracy and reinfection risk?

7 June 2011. Related: All topics, HIV reinfection (superinfection), Resistance.

My viral load 4-6 months after infection was around 4800. I had a resistance test at the same time and this showed no resistance.
My question is how accurate is the resistance test? Could it miss resistant strains of virus? Should I ask for another resistance test prior to starting treatment or when I have a higher viral load?

Also, I’m guessing it would be possible to be infected with both resistant and wild-type virus at the same time from the same person (if that person had both types as well) – do you know how would this affect any resistance tests and if this is a possibility?

Thank you for your help.

Answer

Answer: Simon Collins

Hi

Great that you had a resistance test when you were diagnosed. This has been recommended in UK guidelines for over five years but we still sometimes hear about clinics where this is not routinely performed.

Testing this early is important because if you were infected with a strain of HIV that is resistant to one of more current drugs, you need to know this. Although drug resistance becomes harder as you get further away from the time of infection it is still important to test the earlier blood sample in case it can still be detected.

Within six months, most drug resistance would still be detected, so there is no need to test again.

In cases where someone has been reinfected with a different strain of HIV, or has been at risk of reinfection, then it is sometimes recommended to have another resistance test.

Cases of reinfection are usually only found when stable CD4 and viral results dramatically change (either on treatment or off treatment), without another explanation. Reinfection is not common – HIV is probably more difficult to catch a second time than it was the first time. However, enough cases have been reported for this to be a serious consideration if you want to stop using condoms with other HIV-positive people.

If this is important, then knowing your partners viral load and drug resistance are pretty important for deciding the risks of reinfection. It also helps if your partner or partners do not have other sexually transmitted infections, especially hepatitis C (for HIV-positive gay men), which can complicate your HIV.

i-Base has an online course on resistance and resistance testing – lots more info there if you want to dig around :)