Explain how sexually transmitted infections (STIs) are spread and how this…

The idea

STIs pass from person to person mainly through unprotected sexual contact, including exchange of body fluids such as semen, vaginal secretions and blood, and through sharing needles. Chlamydia is caused by a bacterium and often shows no symptoms, so an infected person can spread it without knowing; it can be treated with antibiotics. HIV is a virus that attacks the immune system and is spread through infected blood, semen and other body fluids, for example by unprotected sex or shared needles. Spread is reduced by using barrier contraception such as condoms, screening and treating infected people, avoiding needle sharing, and, for HIV, effective drug treatment that lowers the viral load.

What earns the marks

• Chlamydia is caused by a bacterium; HIV is caused by a virus.
• HIV can also be spread by sharing needles or contact with infected blood.
• Chlamydia can be asymptomatic, so carriers may spread it unknowingly.
• Prevention includes barrier contraception (condoms), screening and treatment, and not sharing needles.
• Chlamydia is treatable with antibiotics; HIV is managed with antiviral drugs that reduce transmission.

Common mistakes and how to put them right

• Saying HIV is a bacterium.

  Put it right: Correct it to a virus, while Chlamydia is the bacterium.

• Claiming STIs spread by casual contact such as sharing food.

  Put it right: Correct it to sexual contact and body-fluid or needle routes.

• Assuming an infected person always shows symptoms.

  Put it right by noting Chlamydia is often symptomless.

• Treating HIV with antibiotics.

  Put it right: Correct it to antiviral drug treatment, with antibiotics for the bacterial Chlamydia.

Exam tips

• Link each named infection to its pathogen type (bacterium or virus) explicitly.
• Give at least one route of spread and one method of prevention for each infection.
• Use precise terms such as barrier contraception and body fluids rather than vague wording.