Dec. 24, 2013— -- Fifty-nine people have tested positive for tuberculosis after being exposed at a Nevada hospital neonatal intensive care unit, according to a report issued by the Southern Nevada Health District.
Dr. Christopher Ohl, an infectious disease expert at Wake Forest Baptist Medical Center, said an outbreak this large tied to a hospital is "extremely unusual."
"Unfortunately, this situation is a hospital epidemiologist's worst nightmare as neonates are highly susceptible to contracting TB and their infections can progress quite rapidly," he said.
Read the 5 things you didn't know about tuberculosis.
A mother and her newborn twins died of tuberculosis at Summerlin Hospital over the summer, prompting an investigation by the Southern Nevada Health District.
Hospital staff didn't realize the infected woman had tuberculosis until after she and one of the twins died and they performed an autopsy, according to KTNV, ABC's Las Vegas affiliate. The other twin was in the NICU being treated without being under quarantine.
The second twin also tested positive for tuberculosis and died in August, health department spokeswoman Stephanie Bethel told ABCNews.com.
Letters went out to hundreds of patients in August, but after hospital employees tested positive for the disease, officials started calling families to get tested immediately this fall. They feared about 140 infants had been exposed between May and August.
Although many of these infants have not undergone all the tests necessary to rule out active or latent tuberculosis, most of them tested negative for the disease. Some test results were inconclusive, and seven infants are currently on preventive treatment, however.
Of the 977 people exposed, two had active tuberculosis infections, 59 had latent infections --meaning they had the bacterium but weren't sick – and 181 had incomplete evaluations, according to the report.