A virus is a microscopic infectious agent, consisting of genetic material like DNA or RNA encased in a protein shell, called a capsid. Some viruses also possess an outer fatty layer known as an envelope. Unlike living cells, viruses cannot replicate on their own; instead, they hijack the machinery of living host cells to make copies of themselves. A common public health concern revolves around how long these viral particles can remain viable and potentially infectious on surfaces outside a host body, influencing the risk of transmission.
Factors Influencing Viral Survival
The duration a virus remains viable on a surface is influenced by environmental conditions and the virus’s inherent characteristics. Temperature plays a significant role; many viruses generally survive longer in cooler environments, while higher temperatures can lead to faster inactivation. Humidity also impacts survival; enveloped viruses might persist better at lower humidity levels, while non-enveloped viruses may favor higher humidity. Exposure to ultraviolet (UV) light, such as from sunlight, can damage a virus’s genetic material, reducing its viability.
The type of surface also dictates how long a virus can last. Viruses tend to survive for extended periods on hard, non-porous materials like stainless steel, plastics, and glass, while porous surfaces such as cloth, paper, and tissues generally lead to a much shorter survival time for viral particles. The structural composition of the virus itself is another determinant; enveloped viruses, like influenza and coronaviruses, are typically more fragile and susceptible to environmental degradation due to their outer lipid layer. Non-enveloped viruses, such as norovirus and rhinovirus, lack this protective envelope, making them more robust and persistent in the environment. Lastly, the initial concentration of viral particles deposited on a surface, known as the viral load, can also affect how long infectious particles remain detectable.
Common Virus Survival Times
Different viruses exhibit varying survival times on surfaces, often expressed in ranges due to the multitude of influencing factors. Influenza viruses, for example, can remain viable on hard surfaces for 24 to 48 hours, though their infectiousness declines after 4 to 9 hours. On porous materials, influenza viruses typically survive for less than 8 to 12 hours. Common cold viruses, primarily rhinoviruses, can persist on hard surfaces for several hours to days, but their ability to cause infection usually lasts up to 24 hours.
Norovirus is resilient and can survive on surfaces for days to weeks. It can remain viable on hard surfaces for up to 42 to 70 days, especially at lower temperatures.
SARS-CoV-2 remains viable on plastic and stainless steel for up to 72 hours, on cardboard for 24 hours, and on copper for about 4 hours. Its infectiousness on surfaces rapidly decreases over time, making transmission from contaminated surfaces less likely than other routes.
Respiratory Syncytial Virus (RSV) can survive for many hours on hard surfaces, with viability reported for up to 8 hours. On softer surfaces, RSV survives for shorter durations, such as up to 20 minutes on skin. A virus being detectable on a surface does not always mean it is still capable of causing infection, as its viability often declines faster than its detectability.
Understanding Surface Transmission
Surface transmission, often referred to as fomite transmission, describes the indirect spread of viruses via contaminated inanimate objects. A fomite is any non-living item, such as a doorknob, tabletop, or keyboard, that can harbor infectious agents. The process typically begins when an infected individual coughs, sneezes, or touches a surface after contacting their eyes, nose, or mouth, thereby shedding viral particles onto it. These particles can then persist on the surface depending on the factors previously discussed.
Subsequently, another person may touch the contaminated surface, picking up the viral particles on their hands. If this individual then touches their own mucous membranes—the eyes, nose, or mouth—the virus can be transferred into their body, potentially leading to infection. While surface transmission is a recognized route, it is one of several ways viruses can spread, alongside direct person-to-person contact and airborne transmission. Common items frequently touched in public and private spaces, such as light switches and mobile phones, can act as conduits for viral spread if not regularly cleaned.
Disinfection and Personal Hygiene
Reducing the risk of viral transmission from surfaces involves effective disinfection and personal hygiene practices. Frequent and thorough handwashing with soap and water is a highly effective measure, as soap physically removes and inactivates many viruses. When soap and water are not readily available, alcohol-based hand sanitizers can serve as an alternative to reduce the viral load on hands.
Regular cleaning and disinfection of frequently touched surfaces are also important. Cleaning involves physically removing dirt, debris, and some germs from surfaces using soap or detergent and water. This step is crucial because disinfectants are less effective on dirty surfaces.
Disinfecting, on the other hand, involves using chemical products, such as bleach solutions or EPA-approved disinfectants, to kill germs on surfaces. Disinfectants require a specific contact time to be effective, meaning the surface must remain wet with the product for a period as indicated on the label.
Beyond cleaning, avoiding touching one’s face, particularly the eyes, nose, and mouth, is a simple yet effective way to prevent self-inoculation after potentially contacting contaminated surfaces. Staying home when experiencing symptoms of illness further helps to prevent the spread of viruses to others and their environment.