salvage therapy – a term for the combination therapy used after someone has developed resistance to three or more classes of HIV drugs. Also called ‘third-line’ or ‘rescue therapy’ or ‘treatment of patients with multidrug resistance’.

sanctuary site – see compartment site.

sarcoma – medical term for cancer that affects bone, cartilage, fat, muscle, blood vessels, skin or other connective tissue.

Cancer: lymphoma and sarcoma.

SC (sub-cutaneous) – under the skin. See IV (intravenous) and IM (intra-muscular).

second-line therapy – the combination of used after your first treatment has failed.

secondary mutation – see minor mutation.

selective pressure – this is when a factor in the environment causes one type of organism to develop and grow in preference to another. With HIV drug resistance, the presence of a drug exerts selective pressure for resistance to develop. It is based on evolution and the concept of ‘survival of the fittest’ theory developed by Charles Darwin.

sensitivity – when referring to the accuracy of a test result, sensitivity refers to the proportion of people with an illness or disease who have a positive test result.

If a test has low sensitivity, then false-negative results are the concern – where people have a condition but it is missed.

If a test has high sensitivity, then people are accurately diagnosed – and only a few people are missed.

For a serious condition, high sensitivity is essential to be able to identify people early.

Online calculator.

See specificity.

sensitivity – when referring to the activity of a drug, sensitive means that a drug still works. As resistance develops a drug becomes less sensitive.

A complete loss of sensitivity implies that a drug is no longer working.

It also means that your partner may benefit from counselling.

seroconversion – the immune reaction when you develop antibodies to a new infection. HIV seroconversion usually starts a couple of week after infection. Because this is when viral load is very high (often millions of copies/mL), this is when symptoms occur.

About 70% people have HIV seroconversion symptoms. Some people become very ill and need immediate ART, and other have no symptoms.

seroreversion – the word for when the baby born to an HIV-positive mother, no longer has the mother’s antibodies to HIV.

severity – a measure of how bad something is.

SIDA – the abbreviation for AIDS in French, Spanish, Italian and Portuguese.

side effect – an unwanted effect from taking a medicine. Sometimes called an adverse event or drug toxicity.

somnolence – feeling sleepy or drowsy, especially during the day.

specificity – when referring to the accuracy of a test result, specificity refers to the proportion of people who do not have an illness or disease who have a negative test result.

If a test has low specificity, the concern is over false-positive results – where people who to not have a condition are wrongly diagnosed as having it.

If a test has high specificity, then people who to not have a condition are correctly ruled out from the condition.

For a serious condition, high specificity is essential to prevent people being unnecessarily treated.

Online calculator.

See sensitivity.

spinal tap – See lumbar puncture.

stage (staging) – the stage of hepatitis infection refers to the amount of scaring (fibrosis), from results from a biposy. It is usually measured on the Metavir scale of 0 to 4, where 0 represents no scarring and 4 cirrhosis, or on the Knodell scale of 0 to 6, where 0 is no scarring and 6 cirrhosis. See grading.

standard deviation (SD) – the standard deviation from a mean average, is a measure of the degree of variation from the mean.

STARHS – this is a type of HIV test that can indicate whether you are likely to have been infected within the last six months. STARHS stands for Serological Testing Algorithm for Recent HIV Seroconversion. In the UK this test is now called RITA (Recent Infection Treatment Algorithm).

steatosis – fatty liver. Build up of fat in the liver. Steatosis worsens liver damage and makes hepatitis C harder to treat.