A fomite is an inanimate object or surface that can become contaminated with infectious agents, such as the SARS-CoV-2 virus, and potentially transmit disease to a new host. Early in the COVID-19 pandemic, public health guidance emphasized stringent cleaning and disinfection protocols for surfaces. This focus stemmed from the belief that surface contact, such as touching a contaminated doorknob, represented a significant pathway for infection. Concern was driven by the knowledge that respiratory viruses can survive outside the body for a limited time.
How Long the Virus Survives on Surfaces
Laboratory studies have explored the persistence of SARS-CoV-2 on various materials, revealing that the virus can remain detectable for significant periods under optimal conditions. Results show wide variability depending on the surface material and the specific environmental factors at the time of testing. On non-porous surfaces such as stainless steel, plastic, and glass, some research indicated the virus could remain viable and infectious for up to two to three days.
Other studies, conducted at approximately 20 degrees Celsius (room temperature), found that the virus could be detected for up to 28 days on smooth, non-porous materials. Survival time on porous surfaces like cardboard was typically shorter, often limited to about 24 hours. Environmental conditions play a major role in viral stability; higher temperatures significantly reduce the virus’s lifespan, with infectivity ceasing within 24 hours at 40 degrees Celsius on some surfaces.
These experiments often measure the presence of viral RNA (genetic material), not necessarily a viable, infectious virus. The half-life, the time it takes for half of the viral particles to degrade, is often measured in hours, typically ranging from five to nine hours on non-porous surfaces. Laboratory settings are designed to maximize virus recovery, which does not reflect the complex dynamics of real-world environments.
Scientific Consensus on Fomite Transmission Risk
Scientific understanding of COVID-19 transmission has evolved, shifting away from the initial high concern over surface contamination. The consensus among major health organizations, including the Centers for Disease Control and Prevention (CDC), is that the principal mode of infection is through exposure to respiratory droplets and aerosols carrying the virus. While fomite transmission is possible, the risk is now considered low.
Epidemiological data and quantitative microbial risk assessments (QMRA) indicate that the likelihood of contracting SARS-CoV-2 from a contaminated surface is minimal. Studies suggest the chance of infection from a single contact is less than 1 in 10,000. This low risk contrasts sharply with the longer survival times observed in laboratory experiments.
The discrepancy between lab results and real-world risk is due to factors that degrade the virus, including air flow, ventilation, and evaporation. Only a small fraction of the virus shed by an infected person lands on surfaces. For infection to occur, a sufficient viral load (estimated to be between 10 and 1,000 viral copies) must be transferred from the surface to the hand and then successfully introduced into the eyes, nose, or mouth. The efficiency of this transfer process is very low.
Practical Strategies for Surface Hygiene
Given the low probability of infection via surfaces, the most effective defense focuses on personal behavior rather than constant deep cleaning. Hand hygiene is the primary barrier to transmission, preventing the transfer of contaminants from surfaces to the face. Washing hands thoroughly with soap and water or using an alcohol-based hand sanitizer is recommended immediately after touching shared or public surfaces.
For surface cleaning, the focus should be on high-touch areas frequently contacted by multiple people, such as door handles, light switches, faucets, and mobile phones. Routine cleaning with simple soap and water is an effective first step, as it physically removes dirt and germs.
Disinfection should follow cleaning, particularly after a known exposure or in a high-traffic area, using products effective against the virus. Acceptable disinfectants include alcohol solutions (70 to 90 percent concentration) or a diluted household bleach solution. Allow the disinfectant to remain wet on the surface for the recommended contact time, as wiping it off too quickly may reduce its effectiveness.