Transmission
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95
ter comparing 50 cities with (Wuhan, China; Tokyo, Japan; Daegu, South Korea; Qom, Iran; Milan, Italy; Paris, France; Seattle, US; and Madrid, Spain ; n=8) and without an important SARS-CoV-2 epidemic (n=42) in the first 10 weeks of 2020, areas with substantial community transmission of the virus had distribution roughly along the 30° N to 50° N latitude corridor with consistently similar weather patterns, consisting of mean temperatures of 5 to 11 °C combined with low specific and absolute humidity (Sajadi 2020). Cold working environments have been proposed to be considered as an occupational risk factor for COVID-19 (Cunningham 2020). A possible association of the incidence of COVID-19 and both reduced solar irradiance and increased population density has been discussed (Guasp 2020). It was also reported that simulated sunlight rapidly inactivated SARS-CoV-2 suspended in either simulated saliva or culture media and dried on stainless steel plates while no significant decay was observed in darkness over 60 minutes (Ratnesar-Shumate 2020). However, another study concluded that transmission was likely to remain high even at warmer temperatures (Sehra 2020) and the epidemics in Brazil and India and the southern US – areas with high temperatures – soon tempered hopes that COVID “simply disappears like a miracle”. Warm and humid summer conditions alone are not sufficient to limit substantially new important outbreaks (Luo 2020, Baker 2020, Collins 2020). One group found a significant negative association between UVI and COVID19 deaths, indicating evidence of the protective role of Ultraviolet-B (UVB) in mitigating COVID-19 deaths (Moozhipurtath 2020). If confirmed via clinical studies, the possibility of mitigating COVID-19 deaths via sensible sunlight exposure or vitamin D intervention would be attractive.
End of Quarantine Infectiousness peaks around a day before symptom onset and declines within a week of symptom onset, and no late linked transmissions (after a patient has had symptoms for about a week) have been documented (Meyerowitz 2020). After suspected or confirmed SARS-CoV-2 infection, people should quarantine until •
10 days since symptoms first appeared and
•
24 hours with no fever without the use of fever-reducing medications and
COVID Reference ENG 006.9
