Group A Streptococcus (GAS) is the bacterium responsible for strep throat, an infection affecting people of all ages, though most common in children. Transmission is primarily person-to-person via respiratory droplets. Understanding how the bacteria moves and survives outside the body addresses concerns about its airborne nature.
How Strep Bacteria Enter the Air
The primary method of transmission is the expulsion of respiratory secretions containing the bacteria (Streptococcus pyogenes) when an infected person coughs, sneezes, or speaks loudly. These expelled particles fall into two categories: large respiratory droplets and smaller aerosols. Strep is predominantly associated with the heavier, larger droplets, which quickly fall onto nearby surfaces or people. While large droplets require close contact, smaller aerosol particles can remain suspended in the air longer and travel farther.
How Long Strep Remains Viable Outside the Body
The survival time of S. pyogenes is highly dependent on whether it is suspended in the air or has landed on an inanimate object.
Airborne Viability
When airborne, the bacteria are contained within microscopic droplets that quickly begin to dry out. Studies have shown that the bacteria can remain viable for up to 20 minutes when suspended in the air. This airborne viability is primarily reduced by desiccation (drying out) and efflorescence (salt crystallization). Lower humidity accelerates this process, reducing the bacteria’s survival time in the air.
Surface Viability (Fomites)
Once the bacteria settle onto surfaces, known as fomites, their survival increases significantly compared to their time in the air. S. pyogenes is a gram-positive bacteria known to persist on dry surfaces for extended periods. The bacteria can remain viable on materials like toys, doorknobs, and fabrics for days, weeks, or even up to several months. This prolonged survival highlights the secondary risk of transmission through indirect contact.
The Infectious Period of a Person with Strep
The most significant factor in transmission is the infectious period of the person carrying the bacteria. An individual infected with strep throat can begin shedding the bacteria and be contagious for a few days before any symptoms appear. The contagious period is at its peak during the acute phase of the illness. If the infection is left untreated, a person can remain contagious for approximately two to three weeks. However, antibiotic treatment drastically shortens this timeline; an infected person typically ceases to be contagious after only 24 hours of starting the prescribed antibiotic medication.
Controlling Airborne Transmission
Mitigating the risk of strep transmission involves practical measures aimed at controlling both droplet spread and surface contamination. Since the bacteria are expelled through respiratory actions, covering the mouth and nose when coughing or sneezing is an effective barrier method. Using a tissue or sneezing into the elbow helps contain the droplets, preventing them from becoming suspended in the air or settling on surfaces.
Hand hygiene is another primary defense, as hands frequently come into contact with both respiratory droplets and contaminated fomites. Frequent and thorough handwashing with soap and water or using an alcohol-based hand sanitizer can effectively remove the bacteria. Furthermore, regularly cleaning and disinfecting high-touch surfaces, such as shared toys, handles, and countertops, helps eliminate the bacteria. Infected individuals should also remain home from school or work until they have been on antibiotics for at least a full 24 hours, ensuring they are no longer actively contagious.