Last week saw some of the biggest daily swings in the number of new reported COVID-19 related deaths in Arizona. But a county health official says those reports don't tell the full story of recent days.
On Monday, the Arizona Department of Health Services website listed zero new reported deaths. The numbers rose and fell through the week, then Friday, the state reported 67 new deaths, Arizona's biggest apparent one-day jump so far.
"The fact that you get so many deaths reported on a particular day doesn't mean they died even within the last few days — sometimes, that deaths occurred weeks earlier," said Pima County Health Director Bob England.
He said that's partly because the system for identifying and reporting those deaths is more complex than some might expect, and data about deaths is going to lag more than other statistics as health officials look back in time to uncover deaths that were previously unreported.
"So sometimes you have people who have already been reported with the disease. They're in the surveillance system. They're known to us, but follow-up has not been done since the time they died, so nobody knew in the surveillance system that they died," he said, noting that's one item on a list of reasons for a lag in reporting. In some cases the result wasn't reported correctly, or a person wasn't tested at all, especially in earlier cases at a time when it was even harder to get tested.
On Friday, ADHS published a blog post referencing that day's relatively huge spike in numbers. State health director Cara Christ wrote, by way of explanation, that the agency had recently implemented "death certificate surveillance" on top of its investigations of known cases. The new surveillance accounted for more than half of the newly reported COVID-19 deaths dating as far back as April 12, the post said.
"What you need to look at is is deaths by date of death, not by date of report. And you always have to know that you're missing some of them recently," England said.
That also means you shouldn't be too quick to conclude that you're seeing a downward trend, he said. A more complete picture can only be expected "after the fact," and that we can ultimately expect an undercount.
"Looking back a month later you can know what your graph says. You can know who died on which day. But at the time — how many people died last week — even that's a tougher thing to say."
He said lag and undercounting issues for COVID-19-related deaths in the state will improve as more testing becomes available. In a May 4 video update, England noted positive signs in the rate of people presenting with COVID-19 symptoms, but said deaths and cases are a less clear picture. He emphasized that there will be a lag in the emergence of any trends resulting from actions to reopen.
"It will take two or three weeks to see the effects of any change we make. So we need to pay really close attention as we do this gradually."