The emergence of a new respiratory virus often raises public concern about the safety of routine activities, such as visiting a grocery store. Many people worry about the potential for infection from touching shared, high-contact objects like a shopping cart handle. This concern centers on fomite transmission, which involves the transfer of a pathogen from a contaminated inanimate object to a person. Understanding how the virus that causes COVID-19, SARS-CoV-2, spreads is necessary to accurately gauge the actual danger posed by these common surfaces.
Understanding Fomite Transmission Risk
The risk of contracting SARS-CoV-2 from touching a grocery cart or other surface is generally considered low. While surface transmission is biologically possible, it is not the main driver of community spread. For an infection to occur this way, a person with the virus must deposit enough infectious viral particles onto the cart handle.
The virus must then survive on the plastic or metal long enough for a second person to touch the handle, pick up an adequate number of particles, and then transfer the virus to their own eyes, nose, or mouth. This multi-step process introduces many opportunities for the virus to become inactivated or for the transfer to fail.
Quantitative microbial risk assessments estimate that the chance of infection from a single contact with a contaminated surface is often less than one in 10,000. Real-world swabbing of high-touch surfaces in grocery stores, including cart handles, frequently fails to detect any viable infectious SARS-CoV-2.
How Long SARS-CoV-2 Survives on Common Surfaces
Laboratory studies conducted under controlled conditions demonstrate that SARS-CoV-2 can persist on non-porous materials for a measurable period. On materials like plastic and stainless steel, the virus has been shown to remain viable for up to 72 hours. On porous surfaces like cardboard, the virus may last up to 24 hours.
These findings reflect ideal conditions where the viral material is kept at a stable room temperature and moderate humidity. In reality, the infectious viral load decays exponentially over time, with the half-life on stainless steel and plastic estimated to be only a few hours. Environmental factors outside the lab, such as temperature fluctuations, humidity changes, and exposure to UV light, rapidly inactivate the virus.
Therefore, the mere presence of viral genetic material, which can be detected by testing long after the virus is infectious, does not equate to a real-world risk. The amount of viable virus remaining on a surface after a few hours is drastically reduced, making the likelihood of acquiring an infectious dose from an object low.
Primary Risk Factors in Indoor Public Spaces
The vast majority of SARS-CoV-2 transmission occurs through the air, primarily via the inhalation of respiratory droplets and aerosols. When an infected person breathes, talks, coughs, or sneezes, they expel particles that can carry the virus. Smaller, microscopic aerosols can remain suspended in the air for extended periods, traveling beyond six feet.
The main factors determining the risk of infection in an indoor public setting relate to air quality and human proximity. Poor ventilation is a significant contributor to risk because it allows infectious aerosols to accumulate in the shared air over time, increasing the chance of exposure.
Risk also increases with the duration of exposure and the closeness to an infected person. Standing in a crowded, poorly ventilated checkout line, especially near someone who is speaking loudly or coughing, poses a far greater risk than the brief act of touching a cart handle. Outbreaks are frequently reported in crowded indoor settings where people spend long periods together.
Personal Mitigation Strategies for Shopping
Adopting effective personal measures can significantly reduce the overall risk during a shopping trip. The most effective strategy against airborne transmission is the proper use of a high-quality mask that fits snugly over the nose and mouth. A well-fitted mask reduces the amount of infectious material expelled by the wearer and inhaled by others in the store environment.
Hand hygiene remains the most practical defense against surface-related transmission. It is beneficial to use an alcohol-based hand sanitizer or disinfectant wipe on the cart handle before starting to shop, and immediately after the shopping trip is complete. Avoiding touching your face, including your eyes, nose, and mouth, while shopping is also a habit that prevents the transfer of any particles from your hands into your body.
Maintaining physical distance from others in the store reduces the chance of inhaling respiratory droplets at close range. Whenever possible, try to keep at least six feet between yourself and other shoppers, particularly in areas like aisles or checkout lines where people tend to congregate. These combined practices address both the airborne and surface routes of transmission.