STIs and HIVSpec 16.6.1, 16.6.2, 16.6.3, 16.6.4, 16.6.5
In short
A sexually transmitted infection (STI) is an infection that is transmitted through sexual contact. HIV is a pathogen that causes an STI and may lead to AIDS. HIV spreads by sexual contact, blood-to-blood contact such as shared needles, and from mother to baby. Using condoms, not sharing needles and screening blood all help control its spread.
A sexually transmitted infection (STI) is an infection that is transmitted through sexual contact.
Human immunodeficiency virus (HIV) is a pathogen that causes an STI. HIV infection may lead to AIDS (acquired immune deficiency syndrome). HIV damages the white blood cells of the immune system, so the body finds it harder to fight other infections.
Methods of transmission of HIV
- Sexual contact with an infected person, when body fluids pass from one person to the other.
- Blood-to-blood contact, for example sharing needles used to inject drugs, or infected blood entering a cut.
- From an infected mother to her baby: across the placenta, during birth or in breast milk.
How the spread of STIs is controlled
| Method | How it helps |
|---|---|
| Using a condom | Acts as a barrier so body fluids cannot pass from one person to another |
| Not sharing needles | Stops infected blood passing between people |
| Screening blood used for transfusions | Infected blood is not given to patients |
| Testing and informing partners | People who are infected can be treated and can avoid passing the infection on |
| Drug treatment of infected people | Antiretroviral drugs reduce the amount of HIV in the body, which lowers the chance of passing it on, including from mother to baby |
| Having fewer sexual partners | Reduces the chance of coming into contact with an infected person |
A good answer names the method and says how it works: 'use a condom, which prevents body fluids passing between partners'. Do not say that HIV and AIDS are the same thing: HIV is the virus, AIDS is the condition it may lead to.
Quick check
What is a sexually transmitted infection?
Show answer
An infection that is transmitted through sexual contact.
What may HIV infection lead to?
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AIDS.
Give two ways in which HIV can be transmitted.
Show answer
Any two from: sexual contact, sharing needles or contact with infected blood, from an infected mother to her baby.
How does a condom reduce the spread of STIs?
Show answer
It is a barrier that stops body fluids passing between partners.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026