At least 13 people have died and another 99 have contracted TB in the outbreak in Jacksonville, the state's largest city with a population of 825,000.

The Florida Department of Health said local, state and federal officials were working to contain the infections and that there was no need for a highly publicized alert even though up to 3,000 people may be at risk of contracting TB.

State health officials also defended their decision not to raise a general alarm because the population of infected homeless persons appeared isolated and contained.

"In this particular cluster, the general public was not at risk, because the cluster affected a defined sub-population," Dr. Steven Harris, the department's deputy secretary, told Reuters on Friday.

He said the department's first priority for communicating information about TB cases was to those at highest risk of exposure and added that "it is nearly impossible to catch TB" from casual contact with an infected person on the street.

TB is caused by airborne bacteria spread through coughing or close contact with those already infected.

"To be at risk, you must be exposed to the organisms constantly, by living or working in close quarters with someone who has the active disease," he said, noting that most people who are infected never have symptoms or spread the infection.

TB cases in Florida have steadily declined from 1,764 cases in 1994 to 753 last year.

To help track the spread of the current outbreak in Jacksonville, which was first detected in 2009, Florida's health department called in the Atlanta-based U.S. Centers for Disease Control and Prevention in February.

The CDC, however, said in a report that most of the potentially infected persons remained undetected and mobile, a combination that makes containment and treatment more difficult. Although the TB strain in the Jacksonville outbreak is a common one, it still requires a lengthy course of antibiotics.

The report noted that the outbreak was the largest the CDC had been involved with since the 1990s. It was released in April while lawmakers were debating a bill to close a state hospital in Palm Beach County that handled hard-to-treat TB strains.

Backers of the move to close A.G. Holley State Hospital included Republican Governor Rick Scott, a former health care executive who said the 62-year-old hospital had outlived its usefulness and needed to be shut down to save money.

The bill was passed and signed by Scott in late April and the hospital was closed at the end of June, but lawmakers involved in the decision said they had not been informed of the outbreak in Jacksonville.

"Maybe it's appropriate that A.G. Holley would be closed, maybe not," Senate Minority Leader Nan Rich, a Democrat who voted not to close the hospital, said in a statement on Thursday. "If we had all the information, maybe a different decision would have been made."

Rich, who sits on the Senate healthcare budget committee, has called for a legislative hearing to address the matter.

(Editing by David Adams and Paul Simao)

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