Coronavirus Update 14

A shows droplet counts per time slice (1/60 second)

B shows speech-emitted droplets scattering green laser light

A couple of things merit mention. One old thing is that it is unusual to get a COVID-19 infection from surfaces that contain the virus. A new thing is that data suggests that talking increases droplets a person emits.

Old data

The Washington Post writes:

“No one is touching anything, and everyone is cleaning everything. Despite initial reports warning people that the novel coronavirus can be transmitted from contaminated surfaces, the Centers for Disease Control and Prevention has told Americans in no uncertain terms that the virus is primarily transmitted person-to-person, through breathing, speaking, shouting and singing. While it may be possible to catch covid from a doorknob or a package, it’s a long shot, and “not thought to be the main way the virus spreads,” says the agency. (It still recommends disinfecting high-touch surfaces.) .... the most important things that will help them avoid catching covid-19? Wearing masks, staying more than six feet apart, avoiding enclosed spaces.”

The communications problem: An unintended consequence of extended concern for exercises in mostly ineffective surface disinfecting is that it creates a false sense of security in some people, leading them to be less concerned with the risk of airborne infection. One expert commented on the delicate communications problem. Early experiments with contaminated surfaces used unrealistic virus concentrations of virus that “have little resemblance to real-life scenarios. I do not disagree with erring on the side of caution, but this can go to extremes not justified by the data.”

In other words, keep focused on aerosols, and don't worry so much about possibly contaminated surfaces. Just keep your hands away from your face after touching possibly contaminated surfaces and wash hands later when you can.

New data

Some recent research has generated interesting data about talking. Not surprisingly, talking generates more airborne droplets than not talking. Talking loudly generates more droplets that talking quietly. A recent study found that loud speech can generate thousands of oral fluid droplets per second. That data was interpreted to mean that there is a ‘substantial probability’ that normal speaking causes airborne virus transmission in confined environments. More research is needed to confirm these initial observations.

An earlier short report (some data is shown in the image above) indicated that the number of droplets decreased a lot if a damp cloth covered the speaker's mouth while speaking. So again, both mask wearing and speaking quietly or not at all appears to be helpful, while not wearing a mask or speaking loudly increases the possibility than an infected person can pass the virus to an infected person and cause an infection. In all situations, one is better off outside and distanced from others who might be infected compared to being inside where the droplets can persist in significant numbers for a longer time.

A 2019 paper commented:

“Here we show that the rate of particle emission during normal human speech is positively correlated with the loudness (amplitude) of vocalization, ranging from approximately 1 to 50 particles per second (0.06 to 3 particles per cm3)[1] for low to high amplitudes, regardless of the language spoken (English, Spanish, Mandarin, or Arabic). Furthermore, a small fraction of individuals behaves as ‘speech superemitters,’ consistently releasing an order of magnitude more particles than their peers. .... other unknown physiological factors, varying dramatically among individuals, could affect the probability of respiratory infectious disease transmission, and also help explain the existence of superspreaders who are disproportionately responsible for outbreaks of airborne infectious disease.”

Safety tip, don't be a sloppy (juicy?) talker or a loud talker. And, wear your mask. And, stay outdoors but distanced everywhere.


Footnote:
1. That number shows a lot fewer emitted droplets than the data reported later. I presume the difference is due to a rather insensitive air flow measurement method in the 2019 paper compared to a more sensitive laser light scattering method in the 2020 publications.