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Research > Phase 3 - Systematic literature review

Phase 3 - Systematic literature review

The third systematic literature review of SARS-CoV-2 research published through November 2020 summarizes current research on how the virus is spread, virus attenuation on commonly found materials, and effectiveness of various prevention and decontamination measures.

Key takeaways from the review

  • SARS-CoV-2 is generally understood to spread primarily through virus-containing water droplets expelled from infected persons from sneezes, coughs, speaking, and other respiratory activities. 
    • The virus can be transmitted by people who are asymptomatic or presymptomatic.
    • Large indoor gatherings have been linked to SARS-CoV-2 outbreak clusters
    • Risk of transmission is increased by spending time with other people in indoor environments such as in an office, school, store or restaurant. 
  • Some factors that have been found to increase spread of the virus include:
    • Settings with higher population density, with factors such as number of people per household, neighborhood housing density, multi-story buildings, and limited access to green space and/or open sky
    • Increased exposure time in indoor environments where people congregate and interact, such as offices, restaurants, or choir practice
    • Exposure to bathroom environments and shared plumbing used by infected people. Examples of shared plumbing may be found in office buildings, school dorms, apartment buildings, as well as in private homes
    • Indoor environments with limited air exchange, such as ventilation systems that only recirculate indoor air or buildings that do not have windows that open to the outside
    • Centralized air-conditioning systems, which have been described in one article as favorable environments for virus viability due to low temperatures with extremes in humidity
  • SARS-CoV-2 survives longer on surfaces in cold conditions, dry conditions, and dark conditions away from sunlight.
  • SARS-CoV-2 dissipates on surfaces more quickly in hot conditions, humid conditions, and under direct sunlight.
  • Coming into contact with SARS-CoV-2 on surfaces is not thought to be a primary mode of transmission, but studies show that the virus can remain active on surfaces from hours to many days, depending on conditions. As such, it may be possible for people to get infected by coming into contact with active SARS-CoV-2 on surfaces.
  • Surfaces and objects that are frequently touched by multiple people can be cleaned regularly to remove infectious particles, including SARS-CoV-2. 
    • Surface cleaners that include 70% ethanol (EtOH), 70% isopropanol (IPA), 0.1% hydrogen peroxide (H2O2), or 0.1% sodium laureth sulphate (SLS) should be applied for at least 60 seconds. Personal protective equipment (PPE) should be worn when using a disinfectant or surface cleaner to reduce exposure to potentially harmful chemicals.
  • The Phase 3.1 literature review identified evidence suggesting that transmission via food, food packaging, or water (fresh, tap, or seawater) is not a significant risk, but more studies are likely needed to verify further.
  • Hand hygiene:
    • Washing hands with soap for at least 20 seconds was found to be effective at reducing the risk of transmission of many types of microorganisms, including SARS-CoV-2.
    • Rubbing hands with effective hand sanitizers for at least 45 seconds can reduce risk of contracting COVID-19.
    • Not all hand sanitizing agents consist of the effective formulations recommended by Centers for Disease Control & Prevention (CDC) or World Health Organization (WHO). Ingredient labels need to be checked at time of purchase to ensure selection of effective products. Findings have varied about what strength of ingredients are needed to be effective against SARS-CoV-2, but hand sanitizers with 80% volume/volume (v/v) ethanol or greater than 75% v/v isopropanol have been found to be effective.
    • Some documented concerns with these cleaning agents:
      • Increased hand cleaning over time has been found to contribute to skin sensitivity and eczema. Protective skincare behaviors are needed for those who are washing their hands frequently.
      • The formulations for most soaps and hand sanitizer are nonbiodegradable, can contribute to antimicrobial resistance, can be hazardous, and are toxic to both humans and the environment.
  • Consistent mask-wearing when around other people reduces the risk of transmission, especially when combined with social distancing and handwashing.
    • Although cloth masks seem to reduce risk, N95s and surgical masks have been demonstrated to be most effective. Homemade masks should be washed regularly.
    • Researchers are developing innovations in mask technology that incorporate such things as sensors, smartphone integration, and state-of-the-art fabrics.
  • Continuous circulation of fresh outdoor air is effective for reducing the risk of transmission, as is the use of portable air cleaners with regularly cleaned HEPA filters. [See CDC guidance on ventilation.]
  • Studies have shown ultraviolet-C (UVC) lights may be an effective way to inactivate the virus. However, the use of UV light to disinfect surfaces may include some health risks. Anyone considering the use of UV light as a disinfecting tool should follow current FDA guidelines and refer to other resources such as the REALM and NEDCC webpages.  Additionally, the potential for damage to sensitive collection materials must also be considered.
  • Research into other interventions is ongoing. Interventions that have been found to be effective as decontamination tactics but need further study include:
    • Mouthwashes and nasal sprays that eradicate virus particles from the respiratory tract
    • Efficacy of decontamination booths, “smart” handwashing stations, and cleaning tunnels
    • Decontaminating surfaces with cold plasma 
    • Inactivating airborne virus with gaseous ozone and dry fogging with an aerosolized mixture of peroxyacetic acid and hydrogen peroxide (aPAA/HP). The potential for damage to sensitive collection materials must also be considered
    • Applying antimicrobial surfaces and coatings to help deactivate the virus on high-touch surfaces; for example, cold-spraying copper on stainless steel surfaces, treating polycotton fabric with DuritexTM—a natural biopolymer and disinfectant, or installing nanostructured aluminum AL 6063 surfaces

Notes for the reader

As you read this systematic literature review, keep in mind a few key points:

  1. The research and information captured in the findings include both peer-reviewed and non-peer-reviewed studies. In the interest of publishing emerging research related to the COVID-19 pandemic as quickly as possible, publication has been expedited rather than waiting for time-intensive peer review.
  2. The studies included in the review have been conducted by different researchers, under different conditions, likely using different concentrations—and possibly sources—of the virus. This makes it difficult for a reviewer to make a straight comparison across studies; and, interpreting the results may be challenging for readers without a science background.
  3. The review includes findings for industries, such as health care, that operate under considerably different constraints and risk factors than do libraries, archives, and museums (LAMs). However, it was important to consider a broad range of available research to determine what may be applicable to LAM operations and identify what research gaps exist. The research captured in the review does not represent recommendations or guidance for LAMs.
  4. The Phase 1 literature review was released in June 2020. The Phase 2 literature review was released in October 2020.
  5. A helpful resource for those interested in tracking the "known unknowns" about this virus is the DHS Master Question List for COVID-19 (caused by SARS-CoV-2)

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