CALDWELL,ID -- Health officials in southwest Idaho have notified more than 500 people they might have contracted tuberculosis while at the Canyon County Work-Release Center in Caldwell.

Now, Canyon County is trying to stop this infection before it gets worse.

Tuberculosis is a contagious disease caused by bacteria that usually attacks the lungs.

It can be spread through the air when the bacteria is inhaled.

"Well, it’s important, TB is a serious disease," said Jennifer Tripp, epidemiologist.

Serious and infectious.  The inmate in question spent five months in the center with active tuberculosis -- cohabitating with hundreds of other inmates.

Southwest District Health sent out 500 letters to those who may have come in contact with the inmate, but so far only 40 of those recipients have responded.  With nine people already testing positive with the less serious, latent form of the disease, health care workers are urging others on the mailing list to react.

"You can't prevent active disease unless you know you have latent disease, so we want to make sure they know if they're infected and receive treatment if that's the case," said Tripp.

Canyon County voluntarily tests new inmates for TB every seven days, but those within the work release program are responsible for their own health care. While it was requested that they be tested, it was not mandatory.

As a result, Sheriff Chris Smith says this one inmate slipped through the cracks.

"He definitely did and we believe he had an indication he was positive which is why he didn't go get the test," said Smith.

Since this case, the rules have changed.  TB testing is now a required for work release participants.  But Smith admits there will always be flaws in the system.

“Is it going to be perfect? I doubt it,” said Smith.  "We hold a lot of inmates here and something else will pop up tomorrow, that's just the way it is.”

Active TB is relatively rare -- Southwest District Health only sees one or two cases a year within its six county jails.

The last time TB affected the jail system here was five years ago.

People can be infected with latent TB but never develop symptoms. 

But those with active TB can experience a bad cough lasting three weeks or longer and chest pain.

Associated Press contributed to this report.