Years ago, while spending a summer in Los Angeles, I fell cripplingly ill. I could not get out of bed. My spine was racked with pain. Being an idiot, I did not call a doctor. But after a week or so, I got better. I started walking my dog again and went straight to our usual park. There, nailed to a tree, was a sign that read, “Be aware, people have been catching West Nile virus from mosquitoes in this park.”

I would have liked to have gotten notification while I was sick: I might have called a doctor. Even better, I wish the poster had been up earlier: I might have switched parks.

The poster was a form of contact tracing — alerting unwitting people to the danger of infection so they can take appropriate action.

The more common form of contact tracing is a phone call from a human being. It works like this: When someone tests positive for a disease, community health officials interview that individual about the people they can remember interacting with over the previous few weeks. Those people are then warned about possible exposure and asked to get a test. If they turn out to be infected, their contacts are also informed. It’s a public health technique that has been used for decades to contain tuberculosis and measles epidemics, as well as HIV/AIDS.

Today, contact tracing and diagnostic testing are the anchors of any successful response to covid-19, regardless of whether the strategy being pursued is mitigation or suppression of the disease. Mitigation uses just enough of both techniques to slow the disease down some but not enough to eradicate it. Suppression, in contrast, involves a surge of testing and tracing strong enough to interrupt chains of transmission and get case incidence down to pretty near zero. Suppression, if you can do it, is obviously the better strategy choice.

The White House has chosen mitigation as the nation’s baseline policy — at best settling for a gentleman’s C for effort. Which means that places that skimp on testing and tracing are likely to get a second wave: Even before the mass demonstrations against racism, 24 states were estimated to have rising rates of infection. We’re seeing the results of the mitigation strategy in the numbers of cases now in Arizona, Texas and Florida.

But in some localities, such as New Orleans, there are strivers at the helm who are going for an A: full suppression. The results were visible in April in a quick return to a very low level of case incidence from a high peak. Unfortunately, thanks to less ambitious efforts elsewhere in the country, New Orleans can count on repeat reintroductions of the disease. The city will have to keep up its hard work for longer than would be the case if everyone had pursued suppression upfront.

Across all contexts, strategies and case-incidence levels, we will need contact tracing for the foreseeable future.

What does all this mean for you?

Know your status.

Know the case-incidence level and trend in your community. If your public health leaders are not providing that information, ask for it.

Know whether your community public health leaders have chosen mitigation or suppression. If they haven’t told you, find out.

Know your personal status. If you think you’ve been exposed in the past, seek an antibody test. If you think you’ve been recently exposed, seek a diagnostic test.

For me, the scariest thing is that as many as 50 percent of transmissions come from people without symptoms or prior to symptom onset. That’s why I embrace contact tracing.

What about digital contact tracing?

When I thought I might be infected with covid-19 (we had a few cases in my office), I had two separate concerns: I might have unknowingly infected my family or close associates, or I might have unknowingly infected strangers in public spaces. Manual contact tracing helps with the first concern; digital tracing, with the second.

Speculation by Fox News and the president about covid-19 cures is making it more difficult for health officials to do their job, says media critic Erik Wemple. (The Washington Post)

Our phones can be that poster in the Los Angeles park. Instead of happening to see a public notice, we can get a targeted ping when a stranger with whom we’ve crossed paths reports a positive test to a data-management system linked to an opt-in phone app. Then the app can tell you your status: “Be aware, you may have been exposed in a public place.” So, yes, if the tools are well-regulated to block data commercialization, I will eventually welcome privacy-protective versions of digital tracing when it arrives.

What will the pandemic mean for each of us for the foreseeable future? It means: Know your status. Embrace contact tracing. Take the call. Take the test.

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