Summertime time is swimming time. But the coronavirus pandemic this year has been a major buzzkill. The question though remains: can you get infected with the new coronavirus while swimming in a public pool? In theory, this is possible, but practically unlikely.
Possible but unlikely
The good news is that so far there has not been a single known case in which people have been infected by water with the coronavirus. This applies not only to swimming pools, but also to drinking water – and there is currently no evidence that the virus in water is contagious at all. However, so far only a few studies have dealt with the topic, so that a transmission during bathing cannot be ruled out with certainty. It is at least theoretically possible to get infected via swimming or bathing water but the risk remains low.
Coronaviruses are resistant enough to remain detectable in water for a few days, several studies have shown. You don’t even have to get the water directly into your nose to get infected with the airway pathogens dissolved in it: aerosols enriched with microorganisms form above the surface of water bodies.
Viruses in water preferably accumulate together with organic matter such as bacteria, skin scales and feces in a border layer about half a millimeter thick on the surface. The permanent water movement repeatedly atomizes this surface microlayer into fine droplets enriched with microorganisms, which one inhales during bathing.
Coronaviruses not easily transmitted by water
Coronaviruses are not among those pathogens that are easily transmitted by water – such as norovirus, hepatitis, or adenoviruses. These pathogens have a special feature in common that distinguishes them from Sars-CoV-2 and other coronaviruses, explains Regine Szewzyk, who is responsible for microbiological risks at the Federal Environment Agency (Germany). “The classic viruses transmitted via waste water are all nonenveloped viruses that survive much better in the environment.”
Nonenveloped viruses have a stable protein capsule of often geometrically arranged, firmly interlocking protein molecules, while enveloped viruses such as Sars-CoV-2 have a very thin membrane consisting of two liquid molecular layers, which is easily disturbed by foreign substances in the water. “The coronavirus has a very sensitive lipid shell and may survive a few days in the bathing water, while noroviruses may last weeks or months.”
Good for swimmers: The stability of both types of viruses decreases with increasing temperature. For example, in a 2008 study, coronaviruses remained stable in tap water for more than three months at 4 degrees Celsius, and at 23 degrees they disappeared almost completely within 12 days. Chemically enveloped viruses are also more sensitive, especially to oxidizing agents. These include chlorine and ozone, which are used to treat swimming pool water.
For this reason, there is definitely no risk of infection from such treated bathing water, for example in swimming pools. But what about ponds and lakes? Organic suspended particles of natural waters make many viruses unstable. Here, too, in addition to the lower stability of the virus, there are other arguments against a major danger from the coronavirus.
Coughing not an efficient way to introduce large amounts of viruses into a body of water
Experts such as Szewzyk doubt that enough coronaviruses can enter the bathing water to pose a risk of infection. Coughing is simply not an overly efficient way to introduce large amounts of viruses into a body of water. Many pathogens typically in lakes are spread by faeces because they introduce many more viruses in the environment. Waste water contaminated with faeces is also one way the new coronavirus can enter bathing waters, says Regine Szewzyk. “However, we consider it impossible that high concentrations of viruses occur in bathing water in this way.”
In Sars-CoV-2, most evidence suggests that transmission happen by digestive products. Experts repeatedly found its RNA in the stool of the infected, but no infectious viruses. According to Szewzyk, not even RNA has been found in the flow of sewage treatment plants, i.e. the treated wastewater. “In addition, bathing waters are particularly protected from fecal contamination.”
In addition, viruses that spread in this way have, in addition to the stable protein capsule, another special adaptation to this transmission pathway. “We know of viruses such as noroviruses, which are typically transmitted via faeces, that very low concentrations are sufficient for infection.” About one to ten infectious virus particles are enough. Sars-CoV-2, on the other hand, we do not yet know how many viruses a person need to contain for infection; however, the number seems to be much higher. This is not only due to the fact that the virus spreads best when the virus-containing aerosol accumulates in a closed space over a long period of time – but also the probably low importance of contaminated surfaces.
It is also unlikely that bathers release enough virus particles via the throat and nose for direct infection into the water. “The dilution in the water counteracts contagion,” says Szewzyk. Therefore, it is not known at this time whether a transfer to other bathers is possible in this way at all.” Theoretically, however, one can imagine situations in which one is exposed to high virus concentrations in this way.»
Not only in comparison with other pathogens that are more easily spread over water, sars-cov-2 infection is relatively unlikely, but also in terms of the risk of infection via aerosols. However, when many people crowd the water on warm days, the risk of infection increases on the already known paths.
Because mouth-nose protection in the water is rather impractical, one should pay attention to hygiene and disinfection when bathing, experts warn. In particular, toys and bathing equipment such as snorkels, pool noodles and the like should not be shared between children. Also helpful are keeping distance and coughing and sneezing into the elbow – the chlorination in swimming pools also irritates the mucous membranes. However, bathing lakes and outdoor pools are the better alternative anyway: Sars-CoV-2 is spread mainly indoors.
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Hugues Louissaint is an entrepreneur and writer, living in the US for over a decade. He has launched successful products such the Marabou Coffee brand, which has been highly successful in Florida. He has also been a writer for more than 5 years focusing on science, technology, and health. He writes part-time for the Scientific Origin and provides valuable input on a wide range of subjects.