Infection Control Prevention
SARS-CoV-2 is thought to primarily be transmitted through respiratory droplets (WHO, 2020d). When an infected person coughs or sneezes, droplets of respiratory secretions containing the virus travel through the air for a short distance, which can land on another person in close contact. These droplets can also land on surfaces where the SARS-CoV-2 virus can survive for hours to days. A recent study showed that SARS-CoV-2 can survive on cardboard for 24 hours and 72 hours on plastic and stainless steel. If a person touches a surface contaminated with the virus and then their face, they can become infected. SARS-CoV-2 might also be transmitted by aerosols, where the virus remains suspended in the air in small respiratory droplets generated by coughing or sneezing, one study found that SARS-CoV-2 survived in aerosols for 3 hours (van Doremalen et al., 2020). Further studies on SARS-CoV-2 to fully understand how it is transmitted from person to person are required. Viral infections are normally spread by people that show symptoms of the disease, but in the case of COVID-19, the virus can be detected in the respiratory secretions of people that have no symptoms suggesting that they can spread the virus before they become ill (ECDC, 2020b).
The survival of SARS-CoV-2 on surfaces for several days indicates that disinfection of surfaces is needed to prevent the infection being transmitted via this route. Enveloped viruses such as coronaviruses are considered the most susceptible viruses to disinfectants (Geller et al., 2012). A recent study showed that SARS-CoV-2 was inactivated by disinfectants including 1% household bleach and 70% ethanol in 5 minutes (Chin et al., 2020). This suggests that household surfaces would be adequately disinfected with common viricidal disinfectants. PHE (2020c) recommends cleaning hard surfaces with warm soapy water followed by a household disinfectant. Areas contaminated with bodily fluids as well as high touch areas (door handles, bathrooms, etc.) should be cleaned. It is recommended that disposable or rubber gloves and an apron for cleaning to protect the wearer from exposure to the virus and disinfectant should be used.
Previous research has found that coronaviruses do not survive as well on soft surfaces compared to hard surfaces, however, SARS-CoV was able to survive from 5 minutes to 24 hours on cotton (Lai et al., 2005), suggesting that there could still be some risk on contact with clothing or linen from an infected person. Industrial laundry facilities are recommended to treat linen from COVID-19 patients as potentially infectious and handle it in a way that prevents the staff from being exposed e.g. not shaking dirty laundry because this could risk the virus transmitting through the air (PHE, 2020c). Healthcare workers are normally responsible for laundering their own uniforms to save costs to the NHS. In response to COVID-19, PHE now recommends that healthcare worker uniforms are washed by industrial laundry facilities (PHE, 2020d). Previous work found that bacteria can survive domestic laundering of healthcare worker uniforms at low temperatures (Riley et al., 2017) and that they survived to a greater extent during domestic laundering compared to industrial laundering (Nordstrom et al., 2012), where high temperatures and specialist detergents are used. Industrial laundries also have controlled procedures for separating and handling waste, minimising cross contamination and exposure of workers compared to domestic laundering.
Household laundry from COVID-19 patients should be washed at the hottest temperature possible (PHE, 2020c) to inactivate any virus present. Chin et al. (2020). reported that SARS-CoV-2 survived at 37°C for 24 hours and 10 minutes at 56°C, indicating that washing at low temperatures may not inactivate the virus. SARS-CoV was similarly killed after 30 minutes at 56°C (Rabeneau et al., 2005). Soiling (bodily fluids and dirt) can protect microorganisms from being killed by disinfectants and heat (Nandy et al. 2019). Rabeneau et al. (2005) reported that more SARS-CoV virus particles survive heating to 56°C in a 20% protein solution compared to without protein, suggesting that the virus could survive to a greater extent in heavily soiled laundry.
Studies suggest that handwashing is the most effective method to prevent respiratory infections such as the common cold (Turner, 2005). Hand hygiene aims to reduce the load of potentially pathogenic microorganisms deposited on the hands from the environment. The removal of pathogenic microorganisms from the hands interrupts the transmission cycle from human to human and from surface to human (Bolon, 2016).
Handwashing primarily involves the use of unmedicated soap, which is made up of detergents that physically remove microorganisms to wash them away (Bolon, 2016). Soap is also known to kill enveloped viruses like SARS-CoV-2. The hydrophobic groups present in detergents insert into the lipid envelope of viruses causing it to dissolve (Kawahara et al., 2018). Chin et al. (2020) reported that SARS-CoV-2 was inactivated by a hand soap solution within 5-15 minutes. The NHS (2019) and PHE (2020e) state that proper handwashing should take 20 seconds.
Hygienic hand rubs (commonly known as hand sanitizer or hand gels), are also used to maintain hand hygiene, particularly where soap and water is not available. Hygienic hand rubs are alcohol-based formulations that usually contain ≥70% ethanol or isopropyl alcohol. Research has shown that SARS-CoV-2 is completely inactivated by 70% ethanol solution (Chin et al., 2020). Two hygienic hand rub formulations recommended by the WHO (based on 85% ethanol or 75% isopropyl alcohol) inactivated SARS-CoV-2 by 5.9 log10 (99.9999%) in 30 seconds, suggesting that they are suitable for infection control of COVID-19.
Respiratory hygiene is another useful infection control intervention and was promoted by the NHS ‘catch it, bin it, kill it’ campaign. Using a tissue to catch coughs and sneezes prevents respiratory droplets from dispersing through the air. Used tissues should be disposed of and the hands washed to prevent further spread of viruses.
Non-pharmaceutical interventions have been introduced to slow the spread of COVID-19, including self-isolation and social distancing. The aim of these interventions is to reduce the number of people that a COVID-19 patient will infect whilst they have the disease; if the number of people infected by one COVID-19 patients is less than one, the number of total cases decrease (Flaxman et al., 2020).
Self-isolation is where confirmed or suspected COVID-19 cases and close (household) contacts isolated within their home for a period of time to allow them to recover and become non-infectious. Removing social contact from within the community prevents potential transmission events that can lead to others catching the virus.
Social distancing is where social interactions and contact with the public are reduced. This is achieved through avoiding non-essential travel outside of the home and maintaining a minimum 2-meter distance from others. SARS-CoV-2 is mainly spread through respiratory droplets which travel a short distance from the infected person and maintain spatial distance can help minimise the risk of transmission. People with COVID-19 can spread the virus before showing symptoms; reducing social contact completely rather than only isolating of confirmed cases reduce transmission by asymptomatic people (Desai and Patel, 2020; Flaxman et al., 2020; Wilder-Smith and Freedman, 2020).
Humans do not have natural immunity to SARS-CoV-2; immunity is only developed from contracting COVID-19. Immunity to infections can also be induced using vaccines, limiting the spread of the infection by reducing the number of people that are susceptible to it. When the majority of the population are immune to the infection, the chance of someone who is susceptible coming in to contact with an infected person and catching the infection is very low. This called herd immunity (Kindt et al., 2007). Herd immunity can be achieved through the number of people catching the infection but allowing the population to contract COVID-19 would result in a large number of fatalities (Ferguson et al., 2020). Developing a vaccine against SARS-CoV-2 is a high priority to prevent control the infection when social distancing measures are relaxed.
Vaccines are made from dead or weakened microbes, or specific parts of the microbe that the immune system recognise (antigens). Antibodies and other immune proteins circulating in the blood attach to the antigen, allowing white blood cells called phagocytes to engulf (phagocytose) it. The phagocytes then present the antigen to B cells, triggering the humoral immune response. Some B cells develop into plasma cells, which produce antibodies that specifically recognise that antigen and neutralise it. Some B cells also turn in to memory B cells which provide long lasting immunity; if the microbe enters the body again the memory B cells recognise the pathogen and produce antibodies to prevent infection. The cell-mediate immune response is also sometimes triggered by viral vaccines. White blood cells called T cells produce chemicals called cytokines to recruit other types of blood cells to contain the infection, while other T cells kill infected cells to prevent the virus from spreading (Kindt et al., 2007; Clem, 2011; Willey, Sherwood and Woolverton, 2011).
Current research into SARS-CoV-2 vaccines has used genetic analysis and computer modelling of the virus to predict structures that would induce an immune response, with most current work focussing on the spike proteins that protrude from the lipid envelope (Prachar et al., 2020). Vaccines normally take years to develop and many do not perform well enough to be put into use. The traditional route of developing vaccines has been condensed to potentially produce a vaccine more quickly (Lurie et al., 2020). By the 20th March 2020, there were already 2 vaccines in human clinical trials and 42 others in pre-clinical trials (WHO, 2020e).
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