CHICAGO -- Junior doctors quickly learn that exposure to patients' germs is part of the job, but a study suggests many are returning the favor. More than half of doctors in training said in a survey that they'd shown up sick to work, and almost one-third said they'd done it more than once.

Misplaced dedication and fear of letting other doctors down are among reasons the researchers cited as possible explanations.

Dr. Anupam Jena, a medical resident at Massachusetts General Hospital in Boston, developed food poisoning symptoms halfway through an overnight shift last year but said he didn't think he was contagious or that his illness hampered his ability to take care of patients.

Jena, a study co-author, said getting someone else to take over his shift on short notice "was not worth the cost of working while a bit sick." He was not among the survey participants.

The researchers analyzed an anonymous survey of 537 medical residents at 12 hospitals around the country conducted last year by the Accreditation Council for Graduate Medical Education. The response rate was high; the hospitals were not identified. The results appear today in the Journal of the American Medical Association.

Nearly 58 percent of the respondents said they had worked at least once while sick, and 31 percent said they had worked more than once while sick in the previous year. About half said they hadn't had time to see a doctor about their illness.

Dr. Thomas Nasca, the accreditation council's CEO, said residents are trained to put patients' needs above their own but also should recognize that if they're sick, their patients would be better served by having another doctor take care of them.

Residents' training is rigorous and demanding. Many work up to 80 hours a week and sometimes 24 hours a day in hospitals. The atmosphere in some programs is ultra-competitive, and residents may work while sick because they don't want to be seen as slackers, Jena said.