I.S. 143, for example, has for the last decade had an on-site medical clinic, offering immunizations, physical exams and social work.

Lisa Murray went to the plant's on-site clinic, but nurses rushed her to the hospital.

The Tyler Morning Telegraph reported that each participant of the 2011 PEARL was required to visit an on-site clinic after completion of the event.

As late as the 1980's, its on-site clinic registered 16,000 patient visits a year.

St. Luke's-Roosevelt Hospital Center (on-site clinic)

At the company's on-site clinic, costs are "down to about $15 per head per annum," he said.

For employees, on-site clinics can mean faster medical attention and lower out-of-pocket costs, since visits are usually free or carry only a small co-payment.

For employers, on-site clinics can mean gains in worker productivity and lower health-insurance outlays.

"There has been an evolution in this industry," said Stuart Clark, executive vice president of Comprehensive Health Services, which operates dozens of traditional on-site clinics.

A vendor company that runs on-site clinics, for example, could steer patients to its own programs for disease management, say, or smoking cessation, instead of equivalent ones offered by the patient's health insurer.