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Coronavirus cases in China just jumped by 14,000 — but not for the reason you think

“We need to be very careful when interpreting any extremes.”

Workers in a temporary hospital in Hubei province, China, clean around two of the dozens of beds visible in the photograph.
Aerial photo taken on February 12, 2020, shows workers doing cleaning work at a temporary hospital converted from Wuhan Sports Center in Wuhan, central China’s Hubei province.
Xiao Yijiu/Xinhua via Getty

Earlier this week, stories and tweets speculating about a downward trend in the number of cases of Covid-19, the new coronavirus disease, cast a ray of hope on what’s been a remarkably worrisome outbreak.

By Thursday morning, that hopeful tone vanished, as news broke of a surge in the case and death toll — to 60,363 and 1,370, respectively.

While it’s easy to get caught up in the roller coaster of spikes, plateaus, or ticks down each day, here’s the thing: These incremental developments don’t necessarily reflect what’s happening with the disease in real time.

“We have seen a significant spike in the number of reported cases in China but not a significant change in the trajectory of the Covid-19 outbreak,” said the World Health Organization’s Mike Ryan, director of the agency’s health emergencies program, in a news conference Thursday. “This increase is in large part down to a change in how cases are diagnosed and reported.”

He sounded a note of caution: “We need to be very careful when interpreting any extremes.”

That’s because we’re still learning about this disease. Even though it may feel like the coronavirus crisis is dragging on, we’re actually early in the outbreak of a newly discovered virus. The way this disease is being diagnosed and tracked is very much a work in progress. And as more countries get diagnostic tools and come up with their own ways of classifying Covid-19 cases, we will surely be in for more spikes and plateaus that don’t actually tell us much about how the virus is spreading on any given day. The story of the latest coronavirus surge helps explain why.

Why the coronavirus cases spiked overnight

On Thursday, officials in Hubei province, the epicenter of China’s outbreak, added more than 14,000 new coronavirus cases to their tally. That was the single biggest increase in cases recorded in one day. The province’s death count also surged to 1,310, with 242 new deaths.

But, Ryan said, “This is an artifact of the reporting,” not a sign that the outbreak is spreading faster or farther.

So what does this mean?

Early in an epidemic of a new disease, it’s not unusual for health officials to shift the definition of what they consider an official case as they learn about the disease or they grapple with the resources they have to find and diagnose cases. In a single day, they can report a big increase or drop in cases based on the new definition — but that doesn’t mean more or fewer people were sick.

And that’s exactly what happened here. In Hubei province, on February 12 health officials essentially broadened the definition of what could be counted as a case. They decided trained medical professionals could classify a suspected case of Covid-19 as a confirmed one based on findings in chest imaging and a doctor’s analysis.

In other words, a lab result was no longer necessary to consider a case confirmed. The change was made to speed up the finding of new cases, National Health Commission spokesperson Mi Feng said, according to the Associated Press. And it comes at a moment when hospitals in Hubei are overrun and medical equipment is in short supply.

The 14,000 new cases weren’t even new, Ryan added: Many were older cases reclassified based on the new definition.

For now, the rest of China is still using the results of lab tests to count confirmed cases, which is why the surge only appeared in Hubei. It will take time to see the real epidemic curve of Covid-19 — that is, a visual of when exactly cases became sick, not just when they were reported. Until then, we should brace ourselves for more panicked spikes and hopeful dips in this outbreak.

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