Molecular basis for transmission of Streptococcus pyogenes

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Group A streptococcus (Strep A) is a highly lethal bacterium that can cause not only simple sore throats and skin infections, but also more deadly infections such as bloodstream infection and toxic shock. It is a major cause of severe sepsis in people who are otherwise healthy, which is why its effects often seem so devastating. It can also affect women who have recently given birth causing something known as childbed fever, or puerperal sepsis; although very rare, this sadly can result in deaths. Strep A only infects humans, which means that infections almost always result from catching the bacteria from another person. It is believed that throat infections are caught from close contact, by mucus from one person reaching another, or by inhaling large droplets spread from another person close by. Skin infections are believed to result from close contact and touch, particularly when the skin is already broken. This is why precautions such as handwashing, and cleaning surfaces are very important when dealing with vulnerable people who may have wounds, or have recently had a baby.Outbreaks of Strep A occur in hospitals, nurseries, care homes, and prisons; anywhere where people who might be more vulnerable are crowded together. Sometimes these outbreaks carry on, even when precautions like handwashing are being adhered to, or involve people who were never close to one another. This raises the possibility that Strep A might be transmitted in the air, in smaller droplets that can remain in the air for longer than larger droplets. Scarlet fever is another infection caused by Strep A, that mainly affects small children and is very infectious. Recently, we investigated outbreaks of scarlet fever in schools and found evidence in some classrooms that Strep A was indeed present in the air. Many of the otherwise healthy children in the classroom had the same strain of Strep A in their throats, and some were able to cough it out. This means that some outbreaks may indeed be associated with airborne Strep A, and to stop those outbreaks, it may sometimes be necessary to introduce precautions to reduce airborne spread; handwashing alone may not be sufficient. Precautions might include improved ventilation, reducing room occupancy and wearing of masks, similar to what was done at the start of the March 2020 COVID-19 lockdown. Those interventions had a dramatic dampening effect on scarlet fever outbreaks that, at the time, were increasing rapidly. We think some strain types are better at spreading in the air than others. In the UK, we have seen new variants of Strep A emerge that, over a period of 4-5 years, have risen to become dominant. This suggests they have a major advantage over older strain types. Similar to viral variants of COVID-19 that were observed to replace older strain types, we believe that the main basis for advantage will be transmissibility . This project sets out to determine which strains of strep A are most suited to airborne spread and which ones are not, to help public health teams decide how best to deal with an outbreak. The project will also use a technique knowns as TraDIS to try to work out which genes in Strep A allow it to survive in different environments such as 'air', or on different surfaces. This could provide some insight into why bacteria behave differently and might allow us to predict how new clones of bacteria, similar to new variants of COVID19, might behave.