How’s your COVID-19 knowledge?

Note: In this continuing series, local science writer Barry Evans offers a quiz on the COVID-19 pandemic.

1 Compared with the C-19 virus, the pores in a cloth mask are …

(a) About the same size

(b) About 10 times larger

(c) About 100 times larger Answer: (c) The pores in cotton fabric are typically 10,000 to 20,000 nanometers (billionths of a meter) in diameter, compared to about 120 nanometers for the SARS-CoC-2 virus. (About 10,000 viruses would fit in the period at the end of this sentence.)

2 In the absence of a mask, a single sneeze can release into the air …

(a) Two hundred thousand virus particles

(b) Two hundred million virus particles

(c) Two hundred billion virus particles

Answer: (b) A single sneeze releases about 30,000 droplets containing some 200 million virus particles into the air—traveling at about 100 mph.

3 How many virus particles does it take to infect someone?

(a) A hundred

(b) A thousand

(c) A million Answer: (b) Researchers are still working on this, but it appears that as few as one thousand SARS-CoV-2 particles can do the job.

4 When is an infected person most infectious to others?

(a) Immediately after being infected

(b) Just prior to having symptoms (c) A week after having symptoms

Answer: (b)

5 What’s our “community transmitted” situation? As of last Thursday, Humboldt County reported a total of 68 positive cases. The fraction of those cases that were community transmitted (neither in contact with someone who tested positive nor travel-acquired) was:

(a) About 20%

(b) About 40%

(c) About 60%

Answer: (a) As of Thursday, of the 68 cases, 13 are from unknown community infection, with 2 under investigation.

6

Compared with the flu, the C-19 virus spreads…

(a) More easily

(b) About the same

(c) Less easily

Answer: (a). Researchers use the R0 (“R-naught”), or basic reproduction number, to classify how contagious it is. An R0 of 1.0 means that, on average, one person will catch the virus from a single infected person. Currently in the U.S., the C-19 virus has an R0 of 2.2, that is, one infected person will infect 2.2 others on average. For flu, the R0 is about 1.3. (In contrast, measles R0 is 12-18.)

7

The likelihood of getting infected outdoors compared with getting infected indoors is:

(a) Remote

(b) About the same

(c) Much more likely

Answer: (a) For instance, according to a preprint (not peerreviewed) paper published last month, out of 1,245 C-19 cases investigated by Chinese researchers, only two stemmed from outdoors transmission. By far the majority of transmissions occurred at home.

8 In the U.S., the chance of dying if you’re infected is:

(a) 1-2 percent

(b) 2-4 percent

(c) 4-8 percent

Answer: (c) According to Johns Hopkins Coronavirus Resource Center, 6% of known cases of C-19 in the US result in death. The mortality rate varies greatly from country to country (see Johns Hopkins chart for the 10 countries most affected by COVID-19 worldwide). Here in Humboldt, we’re doing OK — as of Thursday, we have no deaths, while 6% of 68 is about 4.