Streptococcus pyogenes is the bacterium responsible for strep throat, which can also lead to conditions like scarlet fever. The bacteria leave the body through respiratory droplets or secretions, contaminating textiles and surfaces (fomites). A common concern is how long the bacteria remain viable outside a host, particularly on clothing, where they may pose a risk of transmission or reinfection. Survival time is highly variable, depending on environmental factors and the initial level of contamination.
Viability of Strep Bacteria on Clothing and Fabrics
The survival time of Streptococcus pyogenes (Group A Strep) on clothing and fabrics can range from a few hours to several weeks, depending on the specific conditions of the environment. While the bacteria generally start to die off rapidly once they are exposed to dry, inhospitable conditions, a small number can persist for surprisingly long periods.
When present on textiles like cotton or polyester, the bacteria’s viability is influenced by the material itself. On cotton, for instance, S. pyogenes has been shown to survive for up to 46 days under laboratory conditions. On synthetic fibers such as polyester, which is common in clothing, survival times have been recorded up to 206 days for various bacteria, including S. pyogenes. Although these long survival times relate to the bacteria being alive, the number of viable bacteria capable of causing an infection, known as the infectious dose, decreases significantly as time passes.
The presence of organic material, such as the mucus or saliva that carried the bacteria, acts as a protective barrier, extending the time the microbes remain viable. Furthermore, the number of bacteria initially deposited on the fabric, known as the inoculum, affects the potential for transmission. A heavily contaminated item, such as a soiled piece of bedding or a plush toy, will maintain a viable population for a longer period than a lightly contaminated one.
Environmental Factors That Affect Bacterial Survival
The wide range of survival times is directly related to the environmental conditions surrounding the contaminated fabric. Moisture is a significant factor because higher air humidity generally favors the longer survival of S. pyogenes on textiles. The bacteria are sensitive to desiccation, which is the process of drying out, so damp clothing or items with residual moisture from respiratory droplets can harbor viable bacteria longer than completely dry items.
Temperature also plays a role in the bacteria’s lifespan outside the body. Room temperature is often conducive to survival, allowing the bacteria to persist for days or weeks. Conversely, extreme heat, such as the high temperatures reached in a typical clothes dryer, is lethal to the organism. Cold temperatures can also affect viability; storing contaminated swabs at refrigeration temperature (+4°C) has been shown to cause a progressive decline in viable bacteria counts, but freezing (-20°C) can preserve them for much longer.
The type of fabric material influences survival because of its absorbency and surface structure. Porous materials like cotton, wool, and silk may offer slightly different survival rates than synthetic fibers, with studies finding median survival periods of several weeks on various textile types.
Effective Laundry and Sanitation Measures
Eradicating S. pyogenes from contaminated clothing and fabrics relies on a combination of mechanical, thermal, and chemical actions during the laundry process. Standard washing with detergent and agitation is effective at removing a substantial quantity of microorganisms through dilution and physical removal. However, to ensure inactivation, specific measures are recommended.
Washing contaminated items in hot water is a highly effective method for destroying the bacteria. A temperature of at least 140°F (60°C) is generally advised for hot-water washing to achieve disinfection. Many modern washing machines have a sanitizing cycle designed to reach these elevated temperatures, which is particularly useful when someone in the household has been ill.
Chemical additives are beneficial, especially when dealing with highly contaminated items. Standard laundry detergent combined with chlorine bleach, if the fabric allows, provides effective disinfection. If bleach is not suitable, using an EPA-registered disinfectant additive can be an alternative. The drying cycle is equally important, as the high heat from a dryer is often the most significant factor in killing any residual bacteria that survived the wash. Contaminated laundry should be dried completely on the highest heat setting that the fabric can tolerate.
Before washing, it is important to handle soiled linens carefully to avoid spreading the bacteria into the air. Individuals should avoid shaking contaminated items, such as bedding, as this can aerosolize the bacteria. Soiled items should be rolled up and placed directly into the washing machine or a designated container.