Five babies tested have positive for tuberculosis in West Texas after a nurse assistant at an El Paso hospital nursery exposed hundreds of infants to the disease between September 2013 and last month.

The El Paso Department of Public Health said Saturday in a statement that none of the children have active TB, the deadly and contagious form of the illness. All five will be offered treatment, although the statement said that four of the children had been vaccinated in the past, meaning their results could be false-positives.

The department also says it is expanding the list of children who may have been exposed by 96, bringing the total to about 850. Authorities say that number could still increase.

So far, 200 babies have undergone X-ray and skin tests, according to the health department.

Hospital officials have said they "should have done more" when the employee's symptoms were revealed during her annual screening in July. She was tested in August and put on leave.

Tuberculosis bacteria typically attack the lungs but can also impact the kidneys and brain and, if left untreated, can be deadly. The bacteria are typically transmitted from person to person through coughs and sneezes.

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