Treatment training manual

2.11 Compartments and sanctuary sites

Some parts of the body are more contained than others and are protected by filters.

These places are called compartments or sanctuary sites.

The filters stops larger drug molecules – and infections – from getting into the sites. Or, for example, they can protect a baby during pregnancy.

The filters can limit both HIV and HIV drugs from moving freely into different compartments.

This means that viral load in these sites can be higher or lower compared to viral load in your blood.

These sites include:

  • The genital tract.
  • The fluid that circulates around the brain and spinal column (called cerebral spinal fluid, or CSF).
  • The brain.
  • The placenta an umbilical cord.

HIV can be a little different in each site. Some drugs get into these sites better than others.

  • Resistance can also be different in different sites. It can develop in one site but then travel to the rest of the body.
  • Viral load can be different in each site.
  • Luckily, an undetectable viral load in blood (below 40 or 50 copies/mL) is usually undetectable in the CSF.
  • But 10% of people with an undetectable viral load in their blood might be detectable in a different site. This difference seems to vary at different times.
  • The PARTNER study showed this difference did not affect risk of HIV transmission. See: U=U.

Understanding compartments can be important for some HIV complications.

For example, brain-related problems often include checking viral load in the CSF. Sometimes this involves using HIV drugs that are good at getting into this site.

HIV generally develops in lymph glands, then blood, then other sites. But because HIV can develop independently in one site, infection can travel in both directions. For example, if drug resistance develops in the CSF, this might cause resistance in the rest of your body.

In practice, because blood is used for most tests, we only look in other sites when there is a problem. But if viral load is undetectable viral load in blood it is usually undetectable evrywhere else.

Reducing HIV in blood and lymph nodes seems to stop HIV related complications in other sites. This is even if HIV drugs don’t get into these sites.

Last updated: 1 January 2023.