Two Philly Doctors Break Down Science Behind COVID-19 Safety Precautions

September marks the sixth month of the Philadelphia area shutdown due to the COVID-19 pandemic. This contagious and deadly new virus is even more dangerous than the flu, and with no vaccine or proven therapies to fight it, the war on COVID-19 relies heavily on non-pharmaceutical interventions.

Major public health organizations such as the CDC and WHO have issued guidelines for COVID-19 regarding social distancing measures and hygiene practices. Many of the recommendations are general, such as closing schools and non-essential businesses. Other guidelines offer specific and quantifiable rules for interpersonal distancing (six feet), hand washing (20 seconds), group gatherings (limit of 10 people), and quarantine for those at risk (14 days). These explicit rules raise the following questions: What is the scientific evidence for such precise recommendations? And do these interventions actually work?

How safe are six feet?

Public health organizations have different specific recommendations for interpersonal distancing. While the CDC’s widely publicized recommendation is six feet, the WHO recommends only one meter (just over three feet). The science behind these guidelines dates back to experiments over a century ago using spaced plates on the ground to measure the distance traveled by respiratory droplets. It was concluded that the larger droplets traveled only short distances and that the contagion could probably spread to others only a few meters from the “infector”.

Contemporary studies question whether six feet of separation is sufficient. Air samples taken six feet from influenza patients contain a sufficient concentration of virus particles to be infectious. Indoor spaces such as offices and shops often have drafts that can circulate particles that remain in the air for long periods of time more widely.

Recent experiments have shown that coughing and sneezing create clouds of droplets that travel up to 27 feet. These observations corroborate the findings of COVID-19 hospital departments where viral air samples have been detected up to 13 feet from infected patients. Therefore, while six feet may be practical, there is no guarantee that even this distance is safe. Conclusion: the farther the distances, the better. For most people, close contact is not completely avoidable during daily activities, which is why wearing a mask is an important addition to social distancing.

How many people can meet safely at one time?

President Donald Trump’s coronavirus guidelines released in March recommended “avoiding social gatherings in groups of more than 10 people.” Locally, the Philadelphia Department of Public Health declared a July 14 moratorium on public gatherings of 50 or more until February 2021, eliminating major in-person events such as the Mummers Parade, concerts and sports. -shows.

It is important to avoid large crowds as it is difficult to maintain social distancing in such situations. The likelihood that one or more participants in a group will be infected depends on two factors: the size of the crowd and the prevalence of the disease. Since the prevalence of the disease in the United States is still unknown, selecting a number at which to cap group gatherings is arbitrary. While there is no definable cap number, the important point to remember is that the potential for transmission will be directly proportional to the number of people in a gathering, and therefore bigger is not better.

Are 14 days sufficient as quarantine for those exposed?

Health organizations consistently recommend that people who have been exposed to COVID-19 self-quarantine for 14 days. The appropriate length of quarantine is determined by the incubation period of the virus. For COVID-19, the average incubation period is around five days, with around 99% of people developing symptoms showing them within two weeks of exposure. A 14-day quarantine period is therefore appropriate.

Does Hand Washing Really Prevent COVID-19?

All health organizations recommend washing your hands frequently with soap for 20 seconds or more. Studies indicate that washing hands takes an average of 10 seconds or less, but research has shown that this short time is insufficient to wash away dirt and germs. Washing with a foam time of at least 20 seconds has been shown to eradicate considerably more germs. A popular trick is to sing “Happy Birthday” twice while lathering. An alternative for Philadelphia sports fans is to sing a verse from the song Eagles Fight – a Philly Special!

Many scientists consider the evidence supporting social interventions to be weak because these measures have not been verified by randomized trials. But the recent widespread resurgence of cases due to the relaxation of social precautions as the country began to reopen has emphatically reconfirmed the importance of these public health measures.

michael savage is Ralph J. Roberts Professor of Cardiology and David fischman is Professor of Medicine at the Sidney Kimmel Medical College at Thomas Jefferson University in Philadelphia.


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Susan W. Lloyd