A number of recent studies point to the benefits. A study by Philip Susser, now a medical student, and Nicolas Ziebarth, a Cornell economist, backs up Chipotle’s theory that paid sick leave could reduce the spread of contagion. Their study, published in the journal Health Services Research, estimated that 45 percent of the American work force does not have paid sick leave; that’s about 50 million workers.

Low-income mothers are particularly likely to work while sick. Another study, by LeaAnne DeRigne of Florida Atlantic University and colleagues, explains why. It found that families with less ability to afford unpaid time off are more likely to lack paid sick leave. According to the study, published in Health Affairs, 65 percent of families with incomes below $35,000 had no paid sick leave, while the same was true of only 25 percent of families with annual incomes above $100,000.

Paid sick leave slows the spread of disease. Cities and states that require employers to offer paid sick leave — Washington, D.C.; Seattle; New York City; and Philadelphia, as well as Connecticut, California, Massachusetts and Oregon — have fewer cases of seasonal flu than other comparable cities and states. Flu rates would fall 5 percent if paid sick leave were universal. According to one estimate, an additional seven million people contracted the H1N1 flu virus in 2009 because employees came to work while infected. The illnesses led to 1,500 additional deaths.

Paid sick leave has other benefits besides reducing flu deaths. For example, workers may use it for preventive care, forestalling subsequent, more disruptive health problems. Workers lacking paid sick leave are more likely to delay needed medical care, a finding that holds for both insured and uninsured workers. In other words, though health insurance helps people pay for health care, it does nothing to help them afford to take time off to get it.

Sicker workers may be more prone to job-related injuries. One study found that even within industries in which accidents and injuries are relatively more likely — like forestry, mining and construction — workers with paid sick leave experienced fewer of them than workers without it. Another study found that employees who work while sick are more likely to have heart attacks than those who take time off.