What Coronavirus Numbers Can And Can’t Tell Us About The Spread Of The Disease

By Mose Buchele, KUT

Every day, we hear updated COVID-19 numbers: The number of confirmed cases. The number of people hospitalized. The number of people who have died. We know the numbers are going up, and we expect them to continue to rise. But beyond that, it can be difficult to understand what they teach us about the spread of the disease and whether we’re making progress against it.

The streets are empty in downtown Austin last week. (Gabriel C. Perez / KUT)

To make sense of these daily updates, Claus Wilke says, it helps to think of the pandemic as any other natural disaster, like a hurricane or an earthquake. There is one key difference, though: If everyone stays home, the disaster doesn’t happen.

“Psychologically that’s really difficult. It’s one thing if you see the hurricane coming or the earthquake has already happened,” says Wilke, who chairs the Department of Integrative Biology at UT Austin. “But we have to basically take these really severe measures, that, if we do them right, it will feel like it was completely pointless because nothing happened.”

He says that’s a best-case outcome of stay-at-home orders and other emergency measures cities and states have been taking. Because the disease develops slowly but spreads quickly, though, the numbers won’t tell us if these measures are working for at least three weeks.

A Lag In The Numbers

It can take up to two weeks before infected people show symptoms of the coronavirus and, Wilke says, “it takes about three weeks from the day you get infected to the day you die – if you die.”

That means there’s a lag in time between when people take action to slow the spread of the virus and when the effectiveness of that action is reflected in the data.

Americans should expect the numbers of infected people and deaths to rise for weeks after the population starts staying at home. And because of the speed at which the virus spreads, they will probably rise dramatically.

“The case number and the number of deaths doubles approximately every three days,” Wilke says. “In Italy, they started quarantining late and then it was just getting worse and worse and worse, while they were putting all these severe restrictions into place. And it can feel like it’s not working.”

“That’s what they’re going to see in New York,” he adds. “It will feel like it’s not working,” even if it is.

No Widespread Testing

There’s a second reason the numbers will keep going up: the lack of early widespread testing.

Texas – and the rest of the U.S. – is far behind other countries in testing people. That means when you see the number of confirmed cases reported, you should assume the real number is much higher. The more testing we do, the more the numbers will rise.

Travis County medical officials, for example, believe there are probably seven times more people infected with the coronavirus than are reflected in the “confirmed” numbers.

Wilke says that puts us at a huge disadvantage in fighting the disease.

The most important thing about testing is not to measure the virus’ spread, he says, but to find out “who is infected and who is not.”

If you test enough to identify all cases, then you can actively begin shutting the virus out of the population.

“We can really tell the people that are infected to absolutely stay home. Anybody who’s been in contact with people that have been infected also has to stay home,” Wilke says. “You should test enough so you catch everybody that is positive.”

The U.S. is far from being able to do that – which brings us back to the shelter-in-place orders.

“If you don’t know who has it and who doesn’t have it, the only thing you can do is assume everybody has it and behave accordingly,” Wilke says.

Flattening The Curve

So, knowing the numbers will likely keep rising, is there a sign of progress you can listen for when you hear the daily updates?

The answer to that is yes – but you have to look at more than just the daily numbers.

That’s where those graphs representing the growth of COVID-19 come in.

One of the things you can see in these graphs is the rate of infection. As that rate slows, the line that was a steep curve up begins to level.

One such graph, published by the Financial Times, shows how quickly virus deaths are doubling, Wilke says.

“The U.S. here is roughly on the ‘doubles every three days’ line,” he says. “Korea very quickly got on the doubles every week line” and so its curve is not as steep.

This is what people mean when they talk about “flattening the curve.” It doesn’t mean the numbers stop going up.

“The cases are still going up very, very rapidly,” Wilke says. “These are deaths, so really scary numbers.”

But they still show progress if they show the spread of the disease is slowing. It is a way of knowing if things like social distancing and stay-at-home orders are working.

The View From Texas

Here’s where Texas could actually have an advantage over some other parts of the country.

The disease didn’t spread in Texas as early as in places like New York or California. That gave officials here the opportunity to intervene earlier, amplifying the effectiveness of shelter-in-place rules and other emergency orders.

“We must not be complacent,” Wilke says. “We really have to make sure we don’t squander that.”

Areas where stay-at-home rules are followed early and strictly can stop the disease from spreading as quickly. But it takes everybody working together to do it, and right now, only some parts of the state are onboard.

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