Beverly Pyle, who manages a nursing unit at the Maryland Shock Trauma Center, can predict when her staff will start calling in sick: after several weeks of large patient loads, demanding medical needs and overtime hours.
"The absences take place a week to 10 days later -- things like sore throats, GI [gastrointestinal] symptoms, fevers," she said.
Absenteeism among the 80 employees Ms. Pyle supervises in the multiple-trauma unit is typically two to three times greater than average during the period following a work overload, she said.
"I suspect a lot of it's due to stress. When the patients get sicker, the nurses get busier, and you can see an increase in [employee] absenteeism coming."
So it came as no surprise to her that scientists at the Common Cold Unit in Britain recently found in a study that people under enduring stress were twice as likely to catch a cold as those who were not stressed.
Working in the emergency room of the Johns Hopkins Hospital, Dr. Julius Goepp finds that prolonged stress over a couple of weeks can make him susceptible to a cold. "You can stave it off, during the period of stress, but you know that it is coming," said the assistant director of emergency pediatrics.
It's not the daily surge of patients, the acute stress of multiple emergencies, the uncertainties of the workday that can cause emergency room workers to come down with colds, Dr. Goepp said.
"People who do well under stress stay in the emergency room; those who don't are unlikely to make it in this job."
Numerous studies have attempted to link stress to illness and serious health effects, but working in what seems to be a stressful job does not necessarily lead to increased sickness.
For Maj. Victor Gregory, commander of the city's busy Western District police station, the question of whether excess stress leads to colds is still unanswered.
"I've thought a lot about that over the years, but the jury is still out, as far as I'm concerned," said Major Gregory, who has a degree in biology. "Officers are exposed to stress, certainly, but I have not seen it as a major factor [in sick calls] from my own observations."
From his own days as a patrolman and later working with the Quick Response Teams, which deal with dangerous emergencies, Major Gregory said he didn't experience that reaction to stressful episodes.
Dr. Frank T. Barranco, chief physician for the city police and fire departments, said his clinic is too busy to keep track of such relationships. "I don't think it happens here," he said, but there is no way to link employee-reported illnesses with stress.
Like the nurses at Shock Trauma or the emergency room personnel at Hopkins, people hired by public safety agencies seem to handle the particular types of stress in those jobs.
Air traffic controllers, who bear responsibility for the safety of thousands of airline passengers every day, seem no more prone to colds during busier periods than slower ones, says Fred Ferrar of the Federal Aviation Administration.
"Our medical people say there is not any support for this theory among air traffic controllers," he said. The lack of a good definition of job stress also hampers such studies, Mr. Ferrar said.
A bus driver or assembly line worker may endure more stress than people in seemingly "dangerous" or exciting occupations, said Dr. Jeffrey V. Johnson, a behavioral scientist at the Johns Hopkins School of Hygiene and Public Health who studies workplace social structures.
The bus driver, for example, must meet a schedule that is out of his control, faced with demanding and possibly hostile passengers, isolated from support of any co-workers, coping with the uncertain frustrations of traffic, with a quick turnaround that provides little chance for relief, Dr. Johnson explained.
While much is written about executive stress and burnout, the blue-collar worker, too, often endures long-term, on-the-job stress that can lead to health problems, he said. "It [an adverse health effect] takes weeks to develop, when the body's defense system starts to let down after prolonged stress."
Stress causes the body to release high levels of stress hormones, such as adrenalin and cortisol, to mobilize against the threat, the "fight or flight" response of our caveman ancestors. It is meant to be temporary.
But if this emergency response is prolonged to deal with chronic stress, the circulatory and immune systems wear down and the body becomes vulnerable to disease, Dr. Johnson said.
Some research shows that stress hormone levels remain elevated for weeks and months after a prolonged period of stress, he said.
Serious health effects, such as premature death, heart attack, stroke, ulcers, clinical depression or substance abuse, have been linked with a stressful environment.
But short-term, proximal effects such as colds, headaches, back pain and upset stomach are also likely to show up as the body's response to stress over time, Dr. Johnson said.