An official at a Texas hospital where a nurse assistant potentially exposed more than 750 infants to tuberculosis said Tuesday that her symptoms were discovered in July but that more than a month passed before she was tested for the infectious lung disease.

The administration of the Providence Memorial Hospital in El Paso "should have done more" when the employee's symptoms were revealed during her annual screening, Sierra Providence Health Network CEO Eric Evans said at a news conference. Sierra Providence is the parent company of a network of hospitals that includes Providence Memorial.

The hospital submitted a corrective action plan to the Centers for Medicare and Medicaid Services on Tuesday and expects its approval, Evans said.

The employee tested positive for active tuberculosis on August 27 and was placed on leave. Health officials believe as many as 751 children may have been exposed to the infected worker between September 2013 — three months before the worker exhibited the first symptoms of the disease — and August this year. Of those, 502 are scheduled for testing in the next three weeks and all babies under six months old are being given preventative medicine, said Director of Public Health in El Paso Robert Resendes.

Fifty-three employees who came into contact with the nurse assistant have been tested but none have active TB, said Enrique Martinez, chief medical officer at Providence Memorial. Two more are pending tests as they were away from work.

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.

Norma Hernandez, the mother of a 9-month-old boy exposed to TB, says her trust in the health care system is shattered.

"I'm afraid to even bring him to the doctor because now I don't know whether he'll be exposed to something else," Hernandez said at the parking lot of the El Paso Department of Public Health, where children were being tested for tuberculosis.

Lee B. Richman, founder of the New Jersey Medical School Global Tuberculosis Institute in Newark, said transmission of the disease requires a lot of exposure over long periods of time.

"Seven hundred is a large number, but I'd bet the house very few are infected," Richman said.

David Dowdy, assistant professor of epidemiology at Johns Hopkins Bloomberg School of Public Health, said often about 1 percent of those exposed become TB latent, which means they have the illness in their body but do not develop it and cannot transmit it. From those who are latent, between 5 percent and 10 percent develop the active form of the disease.

At least twice in the past Providence Memorial Hospital has been sanctioned by the Centers for Medicaid & Medicare Services. In 2011, it failed to assess properly a patient who later committed suicide. In 2012, according to CMS, Providence failed to correctly administer drugs to a patient and keep adequate records.