In Michigan, two coronavirus infections in the same workplace constitutes an outbreak. In New York City, public school buildings must close when two people in two different classrooms catch the virus. But Iowa will not announce coronavirus outbreaks at many businesses unless 10 percent of employees are actively infected, and even 10 percent of students becoming ill may not be enough to close a school.

The nation’s patchwork pandemic response has led to wide disparities in data reporting and even in definitions for basic medical concepts. In the absence of federal standards, states have adopted divergent and sometimes scientifically questionable approaches to disease control, which experts say have allowed the virus to spread.

"If I get things under control but my neighbor is using different criteria and allows more disease, then I’m still in trouble,” said epidemiologist Cyrus Shahpar, chief science officer for coronavirus response at the nonprofit Resolve to Save Lives. “We’re never going to get past this unless we get on the same page.”

A Washington Post investigation last month revealed that Iowa used its loose definition of a workplace outbreak to justify withholding evidence that at least 117 people at the Agri Star Meat and Poultry plant in Postville had been sickened with the coronavirus.

In an email Tuesday, Iowa Department of Health spokeswoman Amy McCoy said, “The definition of outbreak in workplaces is an example of how states can come together to share experiences and provide suggestions for how to approach these issues, but each state still may need to adapt depending on public health needs, state laws, and population sizes and settings.”

McCoy said the state is “balancing what’s happening within critical workforces such as meatpacking and food processing where a large number of Iowans work to help feed the world.”

Critics say the state is also relying on questionable metrics to keep schools open.

Iowa requires schools to conduct at least half of its classes in person unless 15 percent of all tests in the community are positive and at least 10 percent of students call in sick. This threshold is among the highest in the nation. According to the Centers for Disease Control and Prevention, a community test positivity rate of 5 percent suggests that there is a “high risk” of transmission in school buildings.

“We have moved our schools into a situation where it may not be as safe and healthy as recommended by medical professionals,” said Mike Beranek, president of the Iowa State Educators Association.

Beranek, who is on leave from his job as a third-grade teacher in West Des Moines while working for the union, said the rules make it difficult to control outbreaks among students and staff members. Although Iowa does not track or report coronavirus cases in schools, an independent effort led by a couple from Ames has found hundreds of positive diagnoses across the system. In some districts, schools remain open, dozens of students are in quarantine.

To Des Moines Public Schools Superintendent Tom Ahart, the danger was too great. When the Education Department denied the district’s request to delay in-person classes, Ahart filed a lawsuit and ignored the state’s order. Classes in Des Moines have been online-only since early September.

But, under threat of losing accreditation or being forced to add days to the school year, the Des Moines school board voted last week to move to a hybrid model in which students could be in classrooms up to three days a week.

McCoy said that the state’s protocol for determining closures and reporting cases is based on long-standing practices for handling outbreaks of diseases such as the flu, and that schools can apply for waivers to close.

But the coronavirus is far more infectious and dangerous than the flu. Epidemiologists consulted by The Post said keeping kids in classrooms in communities with test positivity rates as high as 14 percent is a recipe for disease spread, especially in a state like Iowa, which does not require people to wear masks indoors.

And a White House Coronavirus Task Force report obtained by The Post warned that Iowa is in the “red zone” for new cases and advised the state to adopt new metrics for reopening schools. The report pointed to West Virginia’s system, which advises schools to go remote if at least two outbreaks occur within two classrooms and requires that all school buildings in a county close when the test positivity rate reaches 5 percent — the threshold recommended by the CDC.

Iowa is among a shrinking number of states that do not report case counts by Zip code — data that is especially useful in sparsely populated areas where counties can encompass wide geographic regions.

“Every jurisdiction choosing its own indicators makes it really hard for community members to understand what’s happening with their outbreak and compare,” Caitlin Rivers, an epidemiologist at Johns Hopkins University, told reporters this summer.

Iowa’s threshold for reporting a workplace outbreak — at least 10 percent of employees infected for certain types of businesses — is unusually lenient. For large businesses such as meatpacking plants and warehouses, that could amount to more than 100 people infected before the public is notified.

In the case of Agri Star Meat and Poultry, an outbreak was never reported even though genetic analysis showed the plant had probably been a nexus of spread. In denying a Freedom of Information Act request from The Post, the Iowa Department of Public Health said it was obligated to report only “active” outbreaks; because of a delay in testing, the majority of positive tests at Agri Star were serology tests, which indicate past infection.

“Using a percentage rather than a number to define an outbreak displays a poor understanding of both public health and mathematics,” said David Michaels, who headed the Occupational Safety and Health Administration in the Obama administration.

Generally, an outbreak is defined as the occurrence of disease beyond the normal background level, said Tara Smith, an epidemiologist at Kent State University in Ohio; the newer or rarer the disease, the lower the threshold.

The Council of State and Territorial Epidemiologists, to which Iowa state epidemiologist Caitlin Pedati belongs, provides a stringent definition for workplace coronavirus outbreaks: “two or more laboratory-confirmed COVID-19 cases among workers at a facility with onset of illness within a 14-day period, who are epidemiologically linked, do not share a household, and are not a close contact of each other outside of the workplace during standard case investigation or contact tracing.”

Iowa’s 10 percent threshold “seems like an unbelievably high bar," acknowledged Jeff Engel, a former executive director of the Council of State and Territorial Epidemiologists who now serves as its senior adviser for coronavirus response.

But Engel noted that state epidemiologists often have to negotiate political pressures, and that Iowa is a state that is highly dependent on its meat industry.

“It’s a constant tension between keeping the economy going and protecting the public health,” he said.

McCoy, from the Iowa Department of Public Health, said that the definition from the Council of State and Territorial Epidemiologists “came out after Iowa had developed its own definition and was already reporting on outbreaks,” and that Pedati herself had been involved in the group’s workshop in which workplace outbreak definitions were proposed.

A spokesman for Iowa Gov. Kim Reynolds (R) declined to comment.

Iowa sits at the extreme end of a vast spectrum of approaches to the coronavirus, Shahpar said. A review of state policies found that the same set of statistics would invoke wildly different responses depending on where they occur. A case rate of nine diagnoses per 100,000 residents per day would be considered “very high” in Michigan, triggering the closure of bars and restaurants, a switch to remote learning and a ban on in-person gatherings. But Oklahoma deems that same case rate to be “low,” and simply suggests that businesses and schools utilize heightened hygiene measures.

Shahpar said states are deciding how they want to approach the pandemic and then setting standards that justify their decision.

“It ultimately means that the amount of risk that you have to live with depends on where you are in the U.S.,” he said.

Policies around school closures are similarly varied. In Florida, where Gov. Ron DeSantis (R) cautioned schools against “sweeping” responses to new infections, classes remain in person even in districts that report dozens of new infections every day. New York City, on the other hand, posts daily “report cards” for every school in the system and requires schools to move online if they see at least two cases in two classrooms.

Setting safety standards and tracking cases in school systems should be a federal responsibility, said Randi Weingarten, president of the 1.7 million-member American Federation of Teachers. Without guidance from the CDC, she argued, reopening policies are being set according to state officials’ political preferences. The governors of all four states that have ordered schools to reopen are Republicans. Of the nine jurisdictions with state-ordered closures, all but West Virginia have Democratic governors.

The lack of CDC guidance has also put the onus of developing a pandemic response on local health departments, most of which have far less expertise than the federal agency.

Jennifer Rombalski, public health director for La Crosse, Wis., said her staff members spent the first few months of the pandemic developing their own guidelines for nursing homes, tools for business and dashboards for reporting coronavirus data.

“In a time like covid-19," she said, "for us to be all working on creating guidance materials at the same time when it should just be so much more coordinated has been really frustrating.”

Even in California, where three confirmed coronavirus infections in a workplace count as an outbreak, this information doesn’t always become public.

Foster Farms, a major poultry processing plant in the Central Valley, started reporting coronavirus infections among its workers to the Merced County Department of Public Health in April, but it took more than two months for the department’s officers to inspect the 1,400-person facility, Director Rebecca Nanyonjo-Kemp said. The department has not listed precise case counts at the plant or other specific facilities since July. And the company’s practice of reporting deaths as “resolved” cases meant that the county was not aware of the true number of fatalities until seven people had died.

Nanyonjo-Kemp said that her office received support from California’s attorney general and other state authorities but that it was difficult to navigate unfamiliar terrain without clear federal guidance.

Except for a partial shutdown between Sept. 1 and 7, the plant has remained open throughout the outbreak. A total of 396 workers have become infected with the virus, and nine have died.

All the while, Foster Farms’ workers were never informed about the cases among their colleagues or the health department’s determination of an outbreak, said United Farm Workers organizer Elizabeth Strater, whose union represents some of the company’s employees.

“Looking back," she said, “it’s like a horror movie, and we just weren’t aware of the other scenes.”

Desmond Butler contributed to this report.

Correction: An earlier version of this article incorrectly reported the dates of Foster Farms closure.