We have a new weapon in the fight against the coronavirus, thanks to a group of enterprising researchers at the @czbiohub.

It’s cheap, sophisticated and shockingly precise https://trib.al/OBYzOVt 

Seven weeks ago, researchers at the University of California San Francisco offered to test everyone living or working within a four-square-block area of San Francisco’s Mission District http://trib.al/OBYzOVt 

This was no simple task:

1,400 front doors were banged on at least five times
All 4,087 official adult residents, including the homeless population, were told about the test in their native tongue http://trib.al/OBYzOVt 

In the end, roughly 3,000 people showed up to be tested over 4 days in late April.

More than 6% of Latinos were infected with Covid-19, most with high viral loads, though many had no symptoms.
Of 981 White people tested, zero were positive http://trib.al/OBYzOVt 

There were several takeaways:

Poor people of color are disproportionately affected
Infectious people are walking around without a clue

But neither of those are the biggest takeaway. The biggest takeaway is this chart http://trib.al/OBYzOVt 

The chart illustrates the genetic relationships of all the Covid-19 cases found in that four-square-block area.

It tells us a lot about how the coronavirus spreads http://trib.al/OBYzOVt 

Sars-CoV-2, the virus that causes Covid-19, mutates very slightly once every two or so transmissions.

These mutations don’t alter the virus meaningfully, but they do allow us to track the path it’s taken http://trib.al/OBYzOVt 

The chart starts in Wuhan with the original virus, and no mutations.

The further down the chart we go, the more the virus has mutated away from the original.

People on the same horizontal line have or had the exact same virus as each other http://trib.al/OBYzOVt 

Let’s look at this cluster: 3 people in one household were infected with the same virus. Not unusual.

It likely entered the household from the resident on the same line. They have the exact same virus but got it earlier, hence they have antibodies http://trib.al/OBYzOVt 

When we know these people are surely connected, then the question becomes: How?

Do they ride the same bus?
Are they having an affair?
Is it a little kid who happened to have played in the park near the child of the household? http://trib.al/OBYzOVt 

By revealing the genetic relationship between the viruses, the diagram exposes the social relationships between people it infects.

Joe DeRisi, co-president of the Biohub explains: "It’s basically a spotlight that tells you where to dig" http://trib.al/OBYzOVt 

The virus doesn’t spread in an orderly way: Each infected person might inject two others on average, but most people infect no one.

This method can lead you not only to the super spreaders, but also to the social activity that’s spreading the disease http://trib.al/OBYzOVt 

It works at opening things up, too. Last week, a pair of workers at a fish-packing plant tested positive for Covid-19.

Usually the fear that special measures weren’t keeping workers safe would have forced the plant to close, but not this time http://trib.al/OBYzOVt 

The @czbiohub found the viruses were genetically far apart, meaning the two workers had contracted the virus independently and outside of work.

The fish-packing plant was able to stay open, and workers were able to stay on their jobs http://trib.al/OBYzOVt