Hospital officials did not learn that the resident had become infected until earlier this month, Charness said. Her diagnosis was confirmed this week, he said.
One in 3 patients with active tuberculosis will die within weeks to months if the disease is not treated with antibiotics, but with appropriate treatment, TB can be cured in 90 percent of patients, according to the National Institutes of Health.
Boston Public Health Commissioner John Auerbach declined to comment last night, saying that a press conference on the matter is scheduled for today.
Charness said the VA hospital plans to e-mail hundreds of members of its staff today and send notices in the mail to the 715 patients who may have been exposed to the disease.
At Cape Cod Hospital, officials said they learned about the infected resident this week. The intern was there between Jan. 3 and Jan. 30, said David Reilly, a hospital spokesman.
''We're working hard to identify all patients and workers who may have been exposed to that person," he said.
A spokesman at Brockton Hospital said that the resident was there for a month about six months ago, but that he did not know the precise dates.
''We have immediately begun the process of identifying any persons who may have had contact with this individual, and we're in the process of contacting anyone who may have been exposed," said Rich Copp, a spokesman for Brockton Hospital.Continued...
Officials at Boston Medical Center could not be reached for comment last night.
At the West Roxbury VA hospital, Charness said officials are identifying people with the greatest likelihood of being exposed to the resident.
He said that if tests come back positive for people for whom they thought exposure was unlikely, they would expand the number of people significantly, to include patients on floors where the resident did not work and family members visiting patients.
''It's entirely possible that no one will be infected, and if a small number of people are infected, they are eminently treatable," Charness said. ''And even those people might not generate the disease."
The hospital is urging everyone it contacts to come in for a free skin test, a two-step process that involves injecting a small amount of fluid called Tuberculin under the skin on the forearm.
The person given the test must return within 48 to 72 hours to have a healthcare worker review the test site. The test is then repeated roughly three months later, at a time when latent infection can be reliably detected.
Only someone with active TB is contagious, and it usually takes lengthy contact to become infected, federal health officials say. On average, people have a 50 percent chance of becoming infected if they spend eight hours a day for six months or 24 hours a day for two months working or living with someone with active TB, according to the National Institutes of Health fact sheet.
About 10 percent of people infected develop active TB, which results in early symptoms including weight loss, fever, night sweats, and loss of appetite.
Tuberculosis has reemerged as a serious public health problem in the United States, according to federal health officials. In 2003, about 15,000 new cases of tuberculosis were reported in the United States, according to the federal Centers for Disease Control and Prevention.
Worldwide, about 8 million people develop active TB each year and 3 million die.
Alice Dembner and Stephen Smith of the Globe staff and Globe correspondents Jennifer Nelson and Scott Goldstein contributed to this report.
 

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By David Abel, Globe Staff