The United States is one of the few wealthy democracies in the world that does not mandate paid sick leave. As a result, roughly 25 percent of American workers have none, leaving many with little choice but to go to work while ill, transmitting infections to co-workers, customers and anyone they might meet on the street or in a crowded subway car.

As a nation, in other words, we are sicker than we need to be. That reality could make a widespread coronavirus outbreak here worse than it would be in a comparable country that takes sick leave seriously. But to find out just how much worse, a fascinating 2017 study offers some clues.

A paper by Stefan Pichler and Nicolas Robert Ziebarth examined what happened in cities that implemented mandatory paid sick leave in the 2000s. San Francisco was the first to do this, in 2007, followed by Washington, Seattle and New York. Connecticut, California and other states also adopted policies.

To find out how these policies affected influenza rates, the researchers culled data from Google Flu trends, a now-shuttered project that tracked influenza-related searches. After establishing that the searches closely tracked official flu rate numbers by the U.S. Centers for Disease Control and Prevention, they used the data to compare influenza rates in cities with and without mandatory paid leave, both before and after the policies were implemented.

Their main findings are shown in the chart below.

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Let’s walk through this, as there’s a lot going on. The thick vertical black line represents the point at which the sick leave cities implemented their policies. The blue line going left to right represents the flu rate in the sick leave cities, relative to those without policies: If that line is lower than the zero or “no change” marker, it means the sick leave cities have a lower flu rate than those without such a policy.

Before implementation there isn’t much difference between sick leave and non-sick leave cities: The blue line hovers near the zero line. After implementation, the blue line plummets; infection rates are as much as 40 percent lower relative to cities without paid leave policies.

That’s significant because it means that, at the population level, cities with paid sick leave policies are considerably healthier than those without them.

The absence of paid sick days creates “a near-guarantee that workers will defy public health warnings and trudge into their workplaces, regardless of symptoms,” as Karen Scott, a doctoral student studying workplace issues at the Massachusetts Institute of Technology, put it recently in The Conversation. “In this way, a manageable health crisis can spiral out of control.”

The service industry — comprising the people who prepare our meals and care for our children — has one of the nation’s lowest rates of paid sick leave in the private sector at 58 percent. The CDC reports, for instance, that “1 in 5 food service workers have reported working at least once in the previous year while sick with vomiting or diarrhea.”

Employers, as well as policymakers who oppose paid leave policies, tend to focus on short-term profitability: If you pay a worker to stay home sick, it’s easy to calculate exactly how much that costs your company.

But they overlook the much larger and harder-to-calculate costs of not having a paid sick leave policy: more workers out sick because of those who are spreading the virus in the workplace, as well as decreased economic demand stemming from greater rates of illness among potential customers.

The CDC, in fact, took a crack at estimating the costs of not providing paid sick leave a few years ago. Using federal data on health-care expenditures, the federal researchers estimated that “providing paid sick leave to workers who lack it might help decrease the number of workdays lost due to flu and similar illnesses by nearly 4 to 11 million per year.” That works out to a total national cost savings of $1 billion to $2 billion each year. That figure doesn’t factor in savings from such related factors as reduced job turnover and lower rates of workplace injury from employees who are trying to carry out their duties while battling illness.

The question policymakers should be asking, then, isn’t “can we afford paid sick days” but rather, “can we afford to live without them?” As the coronavirus bears down on us, that question is more urgent than ever.