Researchers Find TB Reinfections in Homeless

People can be infected twice with tuberculosis, and this may help to explain recent outbreaks of the disease among the homeless, researchers said Wednesday.

Although doctors had thought it unlikely that those who had recovered from tuberculosis would be infected again, health officials in Boston said they have confirmed at least seven cases of reinfection at a shelter for homeless people here.

“You can be reinfected,” said Dr. Edward Nardell of the Massachusetts Public Health Department, whose finding was published in the New England Journal of Medicine.

This means that those thought to be protected from the disease can get it again, and that TB vaccine may be less effective than previously thought, he said.

Tuberculosis is caused by an airborne bacterium that usually infects the lungs and causes a chronic cough and spitting up of blood. The disease can be treated with drugs, but, once infected, the patient always carries the bacteria.

For the study, researchers traced the cause of an outbreak of tuberculosis in a 350-bed shelter for the homeless. A culture of specimens from 22 patients there revealed that all of them had an unusually drug-resistant form of the disease.

Seven of the patients were known to have had the disease previously, and it was considered unlikely that they would have this drug-resistant form.

“This emphasizes the importance of TB among the homeless,” Nardell said. He said the disease often occurs in shelters where many patients may have trouble completing the course of treatment.

“It says that TB transmission can occur even if people have been infected before. That wasn’t thought to be very important before, especially in this country. It says that perhaps in this setting, TB may propagate in a more rapid fashion than we thought possible,” he said.