The Daily Dose: Novel coronavirus can linger up to 14 minutes in the air after talking

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A recent study investigated the possibility that COVID-19 could be transmitted via droplets that form while people are speaking. They compared droplet formation when speaking loudly and moderately. They discovered that a considerable amount are formed in each case. As per the study in PNAS, “In a closed, stagnant air environment, they disappear from the window of view with time constants in the range of 8 to 14 min, which corresponds to droplet nuclei of ca. 4 μm diameter, or 12- to 21-μm droplets prior to dehydration. These observations confirm that there is a substantial probability that normal speaking causes airborne virus transmission in confined environments.” Face masks might not be the ultimate, fool-proof panacea but it’s certainly better than walking into a lingering cloud of coronavirus.

With countries easing into the process of re-opening their economies, contact tracing is considered a key element of doing so successfully and with minimum fatalities. However, there are nuances to the process that needs to be taken into consideration. Timeliness and thoroughness play major roles in determining whether it is effective. An Italian study used the local COVID-19 outbreak to design a contact tracing model. Acting quickly emerged as a major factor. The virus’ reproductive rate was the other, determining how exposed individuals need to be found. The higher the R0, the closer to 100% exposed need to be identified. According to the study, “The model includes the implementation of progressive restrictions after the first case confirmed in Italy (February 21, 2020) and runs until March 25, 2020… We draw scenarios of different containment measures and their impact. Results suggest that the sequence of restrictions posed to mobility and human-to-human interactions have reduced transmission by 45% (42 to 49%)… Although a number of assumptions need to be reexamined, like age structure in social mixing patterns and in the distribution of mobility, hospitalization, and fatality, we conclude that verifiable evidence exists to support the planning of emergency measures.”

A separate study also explored the effectiveness of contact tracing coupled with case isolation. Like the previously mentioned Italian study, the authors determined that time is of the essence. “In most scenarios, highly effective contact tracing and case isolation is enough to control a new outbreak of COVID-19 within 3 months. The probability of control decreases with long delays from symptom onset to isolation, fewer cases ascertained by contact tracing, and increasing transmission before symptoms.”

With everything we know about human evolution and how it may have played out geographically, the picture of evolution in East Asia remains vague. A Chinese study investigated how the two main populations, one from northern China the other from what is currently the Fujian region, mixed. As per the authors, ancient DNA indicates “that the northern genetic signature had begun spreading into southeast China by the time of the late Neolithic 5,000–4,000 years ago. This suggests that farming in East Asia could have spread through mixing of farmers and hunter-gatherers, says Ling Qin, an archaeologist at Peking University in Beijing. That’s different from what ancient-genome studies have found in western Eurasia, where farmers with Middle Eastern ancestry largely replaced hunter-gatherers in Europe.”


IMAGE SOURCE: Creative Commons

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