New York has achieved a positive test rate of 3%. Where do you have it?

Three percent.

It’s the highest number in New York City right now, a critical threshold that triggers restrictions by state and local governments in response to the coronavirus. The mayor of New York has closed public schools at 3%. The governor says a sustained level of 3 percent in the city would result in a ban on indoor dining, the closure of gyms and barbershops and the imposition of a 25-person cap on attendance. places of worship, even as the holidays approach.

But as important as that number is, it seems the city and state can’t agree on whether we’re still there.

This is the situation that unfolded over the past week, with Mayor Bill de Blasio claiming 3% had been achieved, while Governor Andrew M. Cuomo said it was well below. Each relies on its own statistics, which are compiled and reported in different ways. And it turns out that the state and the city cannot agree on which tests to include in the calculation.

The gap can be striking: On Saturday, for example, the city said its seven-day average was 3.11%. Mr. Cuomo’s office, however, slashed the city’s rate by more than half a point, to 2.54%.

In a way, of course, not all numbers are created equal, as Mr. Cuomo’s statistics from the State Department of Health govern a wider range of activities and businesses in all parts of New York. York. But Mr. Cuomo has granted local school districts the right to set their own parameters for school closings, and Mr. de Blasio, who controls the school system, has set that level at 3%.

And so, in the end, it was the city’s numbers that caused the temporary pause in in-person learning in the country’s largest school system.

Why can’t they agree that we’re at 3%?

The cause of the discrepancy lies both in the tests included and in the time frame in which the statistics are reported, leading the mayor and governor to give different numbers every day.

It’s the latest jarring post between two rivals that unfolded throughout the pandemic, adding a level of dysfunction and confusion to the response.

State and city health departments have different accounting rules for tracking the spread of the virus. The state considers a new case to arise on the day the test results arrived. The city dates each new case to the day the sample was provided.

So if an infected person goes to a clinic to have their nose taken on Monday, that sample is often delivered to a lab where it is tested. If these results are reported to health officials on Wednesday, the state and city would record it differently. The state would include it with the tally of new cases on Wednesday, while the city would add it to Monday’s column.

The 3% threshold is based on a seven-day moving average. The day a new case is registered is important.

Another factor is also contributing to the gap, which has received little attention so far: antigen testing. New York State includes testing in its official measurements. But while they’re generally faster, they’re less likely to catch infection in people with low viral loads.

New York City, however, does not include antigen testing, preferring a more sensitive test known as the polymerase chain reaction test. The city only includes in its count PCR tests carried out in a laboratory. That’s why the state – which counts both antigen and PCR testing – may have a higher number of overall cases in New York City, but a lower percentage of positives.

Laboratory PCR tests have long been considered the gold standard because they are unlikely to miss any infections. But some public health experts say much of the PCR testing for the coronavirus is too sensitive, resulting in coronavirus diagnoses for people who carry relatively insignificant amounts of the virus and are likely not contagious.

Antigen tests, which can be performed quickly and inexpensively, detect fragments of coronavirus proteins. But they are more likely to miss cases, including recently infected people who have a lower viral load.

The difference in sensitivity between the two types of tests contributed to a widening gap in positivity rates between city and state.

In fact, the positivity rate of the same group of people – in this case New Yorkers – can vary depending on the number of people who receive antigen tests compared to traditional PCR tests. Antigen tests may fail in some cases when the amount of virus is still low.

Let’s say 1,000 people are tested. Suppose all have a PCR test, and 30 tests are positive, for a positivity rate of 3%. Now suppose that half do an antigen test and the other half do a PCR test. Maybe only 25 tests come back positive, for a positivity rate of 2.5%.

Bill Neidhardt, the mayor’s spokesperson, noted that the city’s decision to exclude antigen testing from positivity rates reflects CDC protocol.

“We believe in our numbers and in our methodology,” he said, before referring to the mayor’s decision on Wednesday to declare the 3% threshold exceeded, rather than adopting the state metric in a last minute attempt to keep schools open.

“Changing a public health standard in mid-morning is not a good idea for clarity and public confidence,” he said.

Gary Holmes, a spokesperson for the state’s health department, said the state had flagged both types of tests “to provide the clearest possible picture of people diagnosed with Covid in a given time period. He added that while there were differences between PCR and antigen testing, the state “has issued detailed guidance on how antigen test results should be interpreted, including when the need to confirmatory testing is recommended or required.

Why is this important?

If New York City hits 3% based on state measures, the governor suggested he would enter a so-called “orange zone,” amid three color-coded restrictions the governor enacted. beginning of October.

According to the governor’s plan, a so-called “red zone” is subject to the most severe restrictions, with bans on mass gatherings, indoor dining and in-person learning. Non-essential businesses would close and church services would be limited to 25 percent of the capacity of places of worship or 10 people, whichever is lower. These areas were used for serious epidemics in Brooklyn in October, leading to protests in some Orthodox Jewish communities where the virus was spreading rapidly.

The “orange zones” – which the governor says the city is at risk of falling into – allow slightly large gatherings and al fresco dining, but schools are closing, as are “high risk” non-essential businesses like barbers and shops. gymnasiums. The precautionary zones – suitably yellow – allow for in-person classes, but ramp up testing and put less stringent caps on meals and gatherings.

These areas are re-evaluated after two weeks, and the metrics for entering and exiting each of those areas involve a complicated mix of data and a hint of deliberation: restrictions can be changed on “expert opinion,” the state says, and include determinations based on local hospitalization rates, or whether outbreaks can be attributed to a single source (such as a prison, congregation, or group residence).

Other factors may include “compliance and enforcement actions taken by local government” as well as more vague standards such as “community cooperation to reduce the spread of the virus”.

Which, of course, could make a simple number – such as 3% – less important.

Can the city act alone?

Based on its metrics, New York has already hit the 3% mark. Yet it may still be some time before companies face restrictions.

Not only do state statistics place the city’s seven-day moving average below this figure, New York City must cross that threshold for 10 consecutive days before the city enters the “orange zone.” “.

Technically, the city could use several workarounds to target companies it decides to help spread the virus. For example, the city’s health ministry could try to shut down any restaurant declaring it a public health threat.

But the governor has broad emergency powers over a range of businesses, ahead of Mr. de Blasio. At press conferences, the mayor sometimes issues a resignation note, saying that some decisions about closures should be left to the governor.

So, for now, New Yorkers will continue to wait for the city to hit 3%… again.