Authors: Antonio Figueras Huerta, Alicia de Andrés Miguel, Ana Allende Prieto, Carlos Pietro de Castro, Gloria Sánchez, Joan Grimalt Obrador.
As temperatures rise, announcing summer, the need to resume, as far as possible, the activities that we associate with summer vacation periods becomes more pressing. We want to enjoy the pools, the pools and stroll along the beaches. But we cannot let our guard down. We have to avoid crowds. We must continue to maintain the distance between people and self-protection measures. Everything depends on us. This applies to beaches, swimming pools, rivers, lakes, pools, jacuzzis, hot springs, spas … To all situations that we can imagine. The fewer people, the lower the probability of contagion.
The main source of SARS-CoV-2 contagion in beaches, swimming pools and other bathing places will undoubtedly be human beings, who are the ones who carry the virus everywhere. The most recent studies show that the virus is very persistent (up to 12 hours) in aerosols, the suspensions of tiny particles that are generated by expelling air.
Humans continuously produce aerosols through normal respiration, which are increased in cases of respiratory diseases, when doing sports and exertion or even when singing. Therefore, people infected with SARS-CoV-2 have the ability to produce viral bioaerosols that can remain infectious for long periods of time after production.
Forms of transmission
These aerosols can be transmitted from person to person directly through respiratory droplets or carried by dust particles or water aerosols from water surfaces. We can be infected and have no symptoms.
The presence of this virus, which is around 120 nanometers (nm) in size, has been detected in small microdroplets between 250 and 1200 nm in diameter, and in droplets larger than 4 microns.
The size distribution of these aerosols, the atmospheric conditions and the presence of dust particles determine the time they remain in suspension and the distance they can travel. In addition, these viral particles are deposited on the surfaces around the person who produces it in an area that will vary depending on the force of the sneeze, cough or the force of the breath.
Therefore, maintaining the distance between people who do not normally live together, both in the water and on the banks and beaches, is the effective way to control the spread of the virus. Logically, these distances should increase depending on the strength and direction of the wind.
In order for the disease to develop, it is necessary to be exposed to a certain amount of viral particles. If we only come across a virus particle, it is unlikely that we will become infected. The more people around us, the more likely we are to expose ourselves to infectious viruses.
In the case of the flu, just being exposed to 10 viruses can lead to infection. In the case of other viruses, millions of viral particles are needed for an infection to occur. If we are exposed to fewer viral particles, the less likely we are to become infected. That is why the amount of infective virus present on a surface is important.
The virus on surfaces
These viral particles deposited on various surfaces can be transferred by the hands to the nose, mouth or eyes, facilitating the transmission of the virus efficiently. This aspect is important in any setting and also in recreational areas for different types of bathing, such as riversides, beaches, areas bordering swimming pools and of course in indoor pools, spas or spas.
There are several studies on the survival and infectivity of SARS-CoV-2 on various surfaces. The data that matters to us is the maximum time in which infectious viruses continue to be detected. A study was recently published in the New England Journal of Medicine in order to determine how long this virus can remain stable on different surfaces, comparing it with its predecessor SARS-Cov, in a controlled laboratory environment.
More recently, The Lancet published another work in which, to determine its viability and infectivity, a virus solution was applied to different surfaces.
The researchers found that it was still detectable on copper for up to four hours, on cardboard for up to 24 hours, and on plastic and steel for up to 72 hours. No infectious virus could be recovered either on printed paper or tissue after a 3 hour incubation. Nor was infective virus detected in wood and fabric treated on the second day.
In contrast, SARS-CoV-2 was more stable on smooth surfaces. No infectious virus could be detected on the fourth day on glass and banknote surfaces, or on the seventh day (stainless steel and plastic). Surprisingly, infectious virus was detected on the outer layer of a surgical mask on the seventh day.
Let’s not forget that these studies were performed in the laboratory.
Scientists are not sure how many SARS-CoV-2 viral particles are needed to trigger the infection. COVID-19 is clearly highly contagious, but this may be because few virus particles are needed for infection to occur (the infectious dose is low) or because infected people release many viruses into their environment.
The virus in wastewater
Other possible routes of contagion, in this case directly related to water, are those derived from the presence of the virus in wastewater that can reach bodies of bathing water and also the survival of the virus from bathers.
SARS-CoV-2 genetic material has been detected in inlet waters of treatment plants. In fact, the possibility offered by measuring the presence of genetic material of the virus to estimate the scope and evolution of the epidemic in the population is being studied in several countries, also in Spain.
On the one hand, it should be noted that the presence of this virus in wastewater from treatment plants is low, which indicates that the risk of environmental contamination of drinking water or beaches is reduced if the wastewater is properly treated.
On the other hand, there is no scientific evidence indicating that these viral residues can lead to infections. Finding genetic material for a virus does not imply that it is infectious. In various places in Europe and in Spain, work is being carried out to determine the presence of infectious viruses in untreated wastewater and everything indicates that this infectivity is low or non-existent.
According to the United States Center for Disease Control (CDC), the virus that causes COVID-19 has been found in untreated wastewater. Researchers do not know if this virus can cause illness if a person is exposed to untreated sewage or sewage systems. There is no evidence to date that this has occurred. Although the logical thing is not to bathe in an area (river or beach) where untreated wastewater flows.
At this time, the risk of transmission of the virus that causes COVID-19 through properly designed and maintained sewage systems is believed to be low. Researchers have analyzed available information suggesting that standard municipal and individual septic system wastewater treatment practices should inactivate the virus that causes COVID-19.
For its part, the “Water and Energy Sustainable Technology” (WEST) center of the University of Arizona, indicates that “although the infected droplets originated by bathers can contaminate the water and the virus has been detected in wastewater, experts are agree that when they reach large bodies of water, the concentration of the virus can be so dilute that it would be difficult to catch it. “
How to inactivate the virus: disinfectants, sun and temperature
SARS-CoV-2 is composed of a core of RNA (the genetic material of the virus) and a protein capsid that surrounds it and, like other respiratory coronaviruses, is covered by a lipid envelope. Coronaviruses can persist both on various inert surfaces, as explained, and in surface and wastewater.
However, according to a WEST report, “Research also suggests that coronaviruses are more sensitive to detergents or products found in water and wastewater treatment processes than non-enveloped enteric viruses (those that cause diarrhea or hepatitis). A or E). Therefore, water and wastewater treatment processes are likely to provide adequate protection against coronaviruses. “
CDC researchers confirm that SARS-COV-2 has not been detected in drinking water and that conventional drinking water treatment methods must eliminate or inactivate the virus that causes COVID-19.
In February of this year there were no specific studies on the efficacy of different disinfectants against SARS-CoV-2, but the data obtained for other coronaviruses, such as SARS-CoV, suggest that the use of a sodium hypochlorite solution at 0 , 1% (equivalent to a 1:50 dilution if the household bleach solution is at the usual concentration of 5%) is effective in inactivating the virus, according to a report by the ECDC (European Center for Disease Prevention and Control) .
A recent study has evaluated the virucidal action of different disinfectants and antiseptics against SARS-CoV-2, including hand soap, 1 and 2% sodium hypochlorite, 70% ethanol, chloroxylenol, povidone iodine, chlorhexidine and benzalkonium chloride.
Except for hand soap, all disinfectants were able to eliminate infectious viruses in 5 minutes. In the case of hand soap, after 15 minutes the presence of infectious viruses was no longer detected.
A common method used for virus inactivation is UVC ultraviolet radiation (200-280 nm) as it coincides with the maximum absorption of nucleic acids (at 254 nm). Furthermore, there are also indications that inactivation occurs more rapidly in seawater than in freshwater due to its salinity.
However, solar UVC does not reach the earth’s surface as it is absorbed by ozone from the atmosphere. Radiation with a wavelength greater than about 300 nm arrives from the Sun, much less effective in inactivating viruses. There are few studies on the inactivation by solar radiation for viruses in water, and none that we know of in sands under ambient conditions, mainly due to the complexity of carrying out experiments that can be extrapolated to real situations.
The impact of sunlight depends strongly on its irradiance (the power of solar radiation per unit area), the quality of the water and the presence of other pathogens and natural organic matter, so that inactivation can vary orders of magnitude depending on the virus, the environmental conditions and the irradiance of the solar UVB which in turn is extremely variable depending on the latitude, time of year, time, atmospheric state, etc …
Therefore, although the Sun is capable of inactivating the virus, with current data it is not possible to estimate the time required to reach a total inactivation for each place, day and atmospheric conditions. A favorable aspect is the buoyancy of the virus, due to its lipid envelope, which keeps it on the surface of the water, facilitating the action of UV radiation.
Furthermore, temperatures above 56 ℃ inactivate SARS-CoV. Reduced survival of SARS-CoV-2 has also been observed at elevated temperatures and a variation in temperature sensitivity depending on the type of surface on which the virus is found.
Temperature is therefore also an effective method for eliminating the virus, which is especially relevant in saunas and steam baths where high temperatures are reached.
Pools and spas
There is consensus that the recommended concentrations of free chlorine (technical-sanitary indications of current regulations) in swimming pool water (1-3 mg / L) are adequate for the inactivation of the virus and therefore sufficient to avoid the risks of contamination bathing in swimming pools and spas and health resorts as long as you correctly and continuously monitor the concentrations of free chlorine present at all times in the bathing water.
In the absence of maintenance personnel, which can happen in private community or private swimming pools, the necessary measures must be implemented to ensure said permanent disinfection.
The CDC’s recommendations for water park managers are summarized in keeping pools adequately clean and sanitized (1-10 ppm free chlorine or 3-8 ppm free bromine and pH between 7.2 and 8).
Before entering this type of facility, the current general recommendations for washing hands and face with soap must be followed. In fact, a soapy shower would be preferable. Likewise, the hygienic conditions of the surrounding areas must be ensured with standard disinfection based on frequent cleaning with diluted bleach or other permitted disinfectants.
According to the CDC, “there is no evidence that the virus that causes COVID-19 can be transmitted to people through water in swimming pools, hot tubs, spas or play areas with water. Proper operation and maintenance (including chlorine or bromine disinfection) of these facilities should inactivate the virus in the water. “
As for the air, there is the possibility of a greater production of aerosols from the surface of the water that can facilitate the transport of the virus. However, it is very likely that the disinfection of swimming pool water works by limiting the viability of possible viral particles in aerosols.
Beaches
No information is available on the ability of this virus to remain infectious in salt water. However, the salinity of seawater facilitates inactivation, in the laboratory. If we have dilution in the body of water, it is not expected that the sea can be an effective means of transmission.
Regarding the sands and border areas, the joint action of the salt in seawater, the solar ultraviolet radiation and the high temperature that the sand can reach are favorable for the inactivation of pathogens.
Untreated fresh water bodies: rivers, lakes, reservoirs …
Studies in other coronaviruses related to SARS-CoV-2 have shown that the viruses remain temporarily infectious in natural freshwater environments. Its survival depends a lot on the water temperature (10 days in water at 23 ℃), the level of organic matter and the presence of antagonistic bacteria (between 2 and 4 days in wastewater).
For lower temperatures, survival increases significantly in both cases. According to reports from WEST and CDC, it is considered that dilution of the virus in water would be able to keep the risk of SARS-CoV-2 low.
However, the survival of SARS-CoV-2 in water from rivers, lakes and pools of fresh and untreated water is higher than that produced in swimming pools and salt water, so precautionary measures must be taken. . In addition to respecting the distance in the outdoor space to the bathing area, it is advisable to control the number of bathers so as not to exceed the precautionary limits to limit the possible viral load present in these bodies of water.
Extreme care in the small pools
We must be more careful in the small pools of still fresh water that many people can go to. This can lead to an increase in viral load.
The coronavirus that causes the pandemic we are currently suffering from is spread from person to person by the same mechanisms as other respiratory viruses such as colds or flu: physical contact with respiratory secretions of infected people, sneezing or coughing. Infected individuals produce a large amount of virus in this area in the initial phase of the disease. In this way, infected people, who develop normal activity, may be spreading the infection without knowing it.
Let’s not forget that we are at the beginning of this book. Many chapters remain in the history of our relationship with this disease. Let’s enjoy the beach, lakes and swimming pools, but behaving in the same way as on land. This summer shouldn’t be like 2019. Let’s not lower our guard. We have to accept that we are the carriers of the virus. We are the ones who take it to the beach and to the pools. The only way to enjoy this summer is by maintaining prudence measures. The distances. Hygiene measures. Let’s avoid crowds so as not to lose what we have achieved with great sacrifice and effort. Only then will we make it more difficult for another outbreak to appear.
This article was originally published on The Conversation. Read the original.
