The persistence of viruses on surfaces represents a risk to human health. Secreted by infected individuals through coughing and sneezing, and therefore carried in the air as bioaerosols, respiratory viruses settle on objects, where they remain viable for varying lengths of time. Upon contact with hands, which act as a vector, contaminated surfaces facilitate the transmission of pathogens to healthy people, who may, in turn, undergo the infectious process. In light of this mechanism, this highlights, once again, the importance of sanitation.
Duration on Plastic, Glass, Fabrics
The survival of viruses on surfaces, together with their ability to retain a certain infectious potential, depends on the coexistence of physical, chemical, and biological factors.
Biological factors include the morphology of the viruses, their genetic organization, and the coexistence of other microorganisms. Chemical factors include pH levels and the presence of antiviral substances, while physical factors include relative humidity, temperature, and ultraviolet radiation. We will focus shortly on these last three factors.
- The impact of relative humidity may differ depending on the virus and its structural characteristics. It is believed that a relative humidity below 50% favors the survival of enveloped viruses. On the other hand, a humidity level above 80% is thought to facilitate the resistance of non-enveloped viruses, as reported in this literature review.
- With regard to temperature, survival conditions appear rather heterogeneous, varying not only as a function of this parameter but also depending on the viral type and concurrent humidity values. In general, high temperatures impair the resistance of viruses in the environment, while refrigeration and freezing are described as protective.
- Exposure to ultraviolet radiation is an inactivating factor for many viruses, as it can compromise their molecular integrity. UV-C light, among other things, is integrated into modern non-chemical sanitation technologies. As explained in this study, resistance to radiation varies according to viral features, with single-stranded viruses being more vulnerable.
Surface features, such as porosity and type of constituent material, add to the physical factors that impact the survival of viruses. Most viral agents, in this regard, persist longer on non-porous materials, albeit with some exceptions. Adenovirus, for example, has been shown to be more resistant on porous surfaces such as paper, while proving weaker on non-porous surfaces such as aluminum and glass.
The following is a brief overview of some commonly encountered materials.
• Metals: stainless steel and aluminum are the predominant materials of many surfaces. Some research has shown that viruses can persist for several days on these materials while maintaining a good level of viability. Stainless steel, in particular, seems to favor prolonged viral persistence thanks to its smooth, non-porous surface. Other metal surfaces, however, can exhibit antimicrobial and antiviral activity, as demonstrated by an investigation on copper and the viability of influenza A virus.
• Plastics and polymers: plastic and polymers are used in industrial processes to produce a wide range of items. Viral survival on these materials, in any case, depends on environmental conditions and on the type of virus. SARS-CoV-2, taken as an example and implicated in the recent pandemic, has been documented in relation to plastic surfaces, on which it can remain viable for about 72 hours.
• Cotton and natural fibers: these fabrics are the predominant materials for clothing and linens (e.g., sheets, towels). Their ability to “support” viruses is generally quite limited, since they absorb moisture and tend to inactivate viral particles.
In conclusion, the survival of viruses on various surfaces depends on a combination of factors, such as the composition of the material, environmental conditions, and the characteristics of the virus itself. Even basic knowledge of this information is useful for targeted sanitation.
Hygiene and Traditional Disinfection
Traditional procedures to make environments healthy include chemical and physical disinfection methods. Chemical disinfection, in particular, uses specific formulations capable of neutralizing microorganisms or inhibiting their proliferation. Physical disinfection, in parallel, exploits the germicidal effects of moist heat, radiation, or other potential measures. In any case, disinfection is preceded by cleaning of visible dirt, using more “coarse” methods (e.g., a cloth).
Understandably, surface contamination varies with the frequency of contact. Surfaces that are touched very often, such as handles and switches, require regular cleaning and disinfection.
Limits of Chemical Products
Chemical products used for surface disinfection are classified by composition and mechanism of action. Prominent formulations, used in multiple contexts, contain alcohols, quaternary ammonium compounds, and chlorine. Each product, moreover, is marketed with specific instructions for correct use. Overall, these are effective measures, although associated with non-negligible adverse effects.
• Environmental impact: the use of chemical disinfectants can significantly affect the environment—namely water, soil, and air quality. For an “ecological” use of such products, it is advisable to follow specific disposal procedures.
• Health risks: if not used correctly, chemical disinfectants can present significant risks to human health. Exposure to these agents can cause skin irritation, respiratory problems, and other adverse effects. The use of personal protective equipment (e.g., gloves, masks, goggles), in addition to compliance with manufacturers’ instructions, makes the use of these agents safer.
In essence, chemical disinfection methods make it possible to act preventively against viral infections, while requiring appropriate behavior and adherence to procedures.
Portable Technologies for Continuous Sanitation
In the context of non-chemical disinfection, there is no shortage of practical and cutting-edge solutions. These include portable sanitation devices, currently implemented with different technologies. They represent a more flexible—yet still effective—variant of fixed devices for indoor spaces. Let us look at two examples available on the market.
- Portable UV-C lamps, which use ultraviolet light. This technology proves effective in neutralizing viruses and bacteria, while requiring, for a good outcome, the coexistence of certain conditions. These concern the light source and its intensity, as well as treatment times and the distance between the radiation and the surface to be treated. The use of UV-C devices, moreover, offers numerous advantages, such as disinfecting hard-to-reach areas and reducing the need for chemical methods.
- e4shield Technologytm: based on the use of an oscillating electromagnetic field, the e4life portable device damages the viral outer envelope, inactivating pathogens present in the surrounding environment. The intensity of the emitted waves meets necessary safety requirements, making it harmless to people and/or animals. Even in the fixed version for indoor spaces, this technology ensures the healthiness of target areas while helping to safeguard the health of their occupants. In this respect, it is proposed as a concrete example of the “One Health” philosophy.
