Group A Streptococcus (GAS) is a bacteria which causes severe infections and leads to deadly diseases such as rheumatic heart disease which kills over 300,000 people a year globally, particularly in low-income countries. We do not know how GAS is spread between people, how often people carry GAS in their throat or on their skin without having symptoms, or what factors increase the chance of this occurring. It is important to understand these factors in order to know how to reduce GAS-related disease. This study will follow 444 people in The Gambia, over 12 months, taking samples from the throats and skin of people living in the same households, and asking questions about themselves and their behaviour, at regular intervals. By taking samples over time, we can understand how common it is to carry GAS without having symptoms, how GAS is spread between people, and whether carrying GAS leads to more GAS infections in people or their household members. We will use state-of-the-art techniques to look at the DNA of GAS bacteria that we find, and combine this with a mathematical model to investigate how different strains spread to people within and between households in the community.