Little information has been released about the contagious individual, who was not a hospital employee or health care worker. The person has since been placed in isolation and is receiving treatment. Officials have cited patient privacy laws in not offering details that could lead to identifying the individual.
The Solano County resident visited Sutter Memorial Hospital in Sacramento during the last half of March and NorthBay Medical Center in Fairfield in early and mid-April.
"We knew who the person was and the person was certainly there for a reason," said Steve Huddleston, a spokesman for NorthBay.
The person was not diagnosed with tuberculosis until late last week and had just recently started showing symptoms, said Dr. Olivia Kasirye, chief public health officer for Sacramento County.
Initially a total of 35 babies were thought to have been exposed at the two hospitals to the bacteria that spreads through the air and can lead to a sometimes fatal respiratory disease, but officials lowered their estimate to 26 at most. Kasirye said 20 babies were thought to have been exposed in Sacramento but further evaluation of hospital records showed only 11 were at potential risk.
Officials said they believed the risk of infection to the infants was low but were asking parents to have the babies tested by their doctors by the end of the week.
Because access to neonatal intensive care units is tightly controlled and records are kept on everyone who comes and goes, the hospitals were able to identify everyone who may have been exposed to the infected person, Kasirye said.
Exposure to tuberculosis often does not lead to the full-blown active version of the disease, in which patients typically come down with a bad cough and chest pain and sometimes cough up blood. Instead, the infection can lie dormant for years, only emerging when a patient's immune system weakens.
Because the babies are already in a vulnerable state, most will likely be placed on an antibiotic to eradicate the germ and prevent the active version of the disease from developing, said Dr. Michael Stacey, chief medical officer for Solano County.
Any adults at the hospital who may have been exposed will also be tested both for their own safety and to gauge how contagious the infected person was at the time, Stacey said. He said initial tests have shown the infection does not appear to be drug-resistant.
In recent years, varieties of tuberculosis that don't respond to standard antibiotics have raised fears that a disease once thought effectively eradicated in the U.S. could become more prevalent.
Last week, California took the unusual step of jailing and charging a tuberculosis patient who they say refused to take medication to keep his disease from becoming contagious. Stacey said the current case is purely a public health issue and that no further investigation is under way as officials focus on making sure everyone possibly exposed is safe.
"This is an unfortunate situation that happened, but it was not the fault of the person or the hospitals," he said.