Too ill to work? Many people, and especially those with paid sick leave, stay home.

However, even people with sick leave regularly engage in “presenteeism” – going to work while ill. It’s the opposite of absenteeism, and its impact on the workplace has been a topic long sequestered in academic journals.

As we head into winter’s cold and flu season, presenteeism is gaining interest in the American workplace for good reason: More costly than absenteeism, it is detrimental to employees and employers alike.

The U.S. Bureau of Labor says 39 percent of all American workers – or 41 million people – do not have paid sick leave. That means a lot of people are showing up for work while under the weather.

In September, President Obama signed an executive order forcing companies holding federal contracts to provide paid sick-leave benefits to their employees.

On the face of it, being sick at work might sound like something employers might favor, with some work preferable to none at all. Besides, such employees display a strong work ethic, job dedication and loyalty. But research generally finds health consequences for present-but-ill employees, with higher medical costs and greater reductions in productivity than absenteeism would cause.

A Society for Human Resource Management online article said presenteeism costs are “higher than the combined costs of medical care, prescription drugs and absenteeism,” with estimated annual costs of $150 billion to $250 billion a year. That represents 60 percent of all productivity losses.

“Unhealthy workers are unproductive workers – and they’re expensive,” stated Scott Wallace, a distinguished fellow at the Geisel School of Medicine at Dartmouth College. And the cost of poor health, he said, can be three to 10 times the total cost of all employee benefits.

That’s why focusing on wellness rather than absenteeism represents a progressive workplace trend.

“This issue is multifaceted, and I think people who ignore it do it with their heads in the sand,” Wallace said. “The impact on employees is tremendous when they show up at work sick. The stress makes them sicker, and their performance level at work is in the gutter.

“People around them get sick, and it increases stress and gets into a death spiral for employers,” he said. “I’m mystified that employers can’t figure this out in 11 seconds.”

Employees who recover at home are more productive than persistently ill employees struggling at work to meet job demands, research shows.

“Organizations need to think about this, develop policies and get first-level managers involved who are closest to the source,” said Gary Johns, a department of management professor at Concordia University in Montreal. He’s reviewed the academic literature addressing corporate and employee impacts of presenteeism.

“Giving employees accommodation and support can be good all the way around,” he said. “They are under so much pressure to go to work that they are contaminating the place or are affecting their own health downstream. But this needs to be managed so you do not burn people out physically and abuse them and create problems.

“It takes a sensitive hand,” he said.

His own published studies note that “a sore throat will stimulate absenteeism for a singer and presenteeism for a pianist.” Reaction from colleagues and clients also affect presenteeism, both as encouragers and discouragers. Teamwork and interdependent work tends to encourage presenteeism.

People earning higher wages generally exhibit less absenteeism. People facing financial difficulties generally were more likely to show up for work when sick.

Ill employees make more mistakes and communicate less effectively and produce lower quality work. Presenteeism among pharmacists, one study found, resulted in more prescription errors. Downsizing actually increases absenteeism. In a real twist, research shows a higher propensity for medical workers to be on the job, even with contagious illnesses.

Job insecurity, strict attendance policies, teamwork, demanding clients and a positive attendance culture are among the factors promoting presenteeism. That, in turn, can exacerbate existing medical conditions, damage the quality of work life and lead to impressions of ineffectiveness because of declines in productivity.

“There’s one thing we seem to know about this,” Johns said. “In the aggregate, it appears that a lot more productivity is lost to presenteeism than absenteeism.”

A delicate balance exists between absenteeism and presenteeism: Are co-workers and superiors aware that a person’s medical condition and productivity are connected? Are accommodations ever made in job design or adjusted performance appraisals?”

While many companies still lack absentee policies beyond forbidding it, few companies have presenteeism policies despite growing evidence of its impact on productivity, said Johns, who holds a Ph.D. in organizational psychology.

“Excitement concerning the subject has been fueled by claims that working while ill causes much more aggregate productivity loss than absenteeism,” states a study he authored in the Journal of Organizational Behavior. “Managing presenteeism effectively would be a distinct source of competitive advantage.”

Other details are clear: People with infectious diseases should stay home or be separated from everyone else. Chronic problems – including back pain, depression and diabetes – are trickier. Johns said there’s considerable agreement across studies that presenteeism accounts for more aggregate productivity loss than absenteeism.

“On the face of it, this suggests an iceberg effect in which the one visible portion of work loss (absenteeism) is dwarfed by that portion beneath the surface (presenteeism),” he stated in one study. “That might result from more sanctions against not attending work vs. taking it easy on the job.”