It's an illness so well known and notorious throughout history and today that it can be commonly identified with a two-letter abbreviation: TB.

Tuberculosis isn't always on the mind of residents of developed nations such as the United States, with 4.4 cases reported for every 100,000 residents in 2007 according to the Centers for Disease Control and Prevention. But the bacterial infection remains prevalent worldwide — with up to one-third of the world's population infected, according to a press release from the Butte County Health Department. Monday was World TB Day, which was intended to raise awareness of TB both abroad and locally.

Most cases of TB are latent, or inactive and noncontagious.

"That can remain dormant for the rest of a person's life," said Dr. Mark Lundberg, Butte County's public health officer.

But those latent cases can become active if not treated. Lundberg estimated 5 percent of TB cases become active within two years of infection and another 5 percent over the remainder of a person's lifetime. It's not known what triggers a case to become active.

TB infections do occur locally, and active cases have seen an increase in several local counties in the last year.

There was one case of active TB in Sutter County in the 2007 fiscal year, said Amerjit Bhattal, assistant human services director for public health. There have been three in 2008.

"So it's gone up a little bit from last year, but fortunately they're cases that can be treated with medication," Bhattal said.

Yuba County has also had three this year, compared to six last year and none the year before that, said Director of Nurses Val Spooner. Butte County has had three active cases every year since 2005, Lundberg said.

Lundberg noted the general public should not go rushing out to be tested for TB, because of the rate of false positive testing. Testing should be limited to those considered "higher risk," which includes people with illnesses such as diabetes, renal disease or HIV infection among others; recent immigrants from regions with high TB rates such as Africa, Asia and parts of South America and eastern Europe; those who extensively travel to high-TB regions, and those who work among high-risk populations.

Tuberculosis treatment is an extensive process with the medication process lasting between six to nine months. Treatment is particularly strong for active cases.

"You start with four different antibiotics," Lundberg said.

Also, most counties use a system called directly observed therapy, or DOT, when dealing with active tuberculosis. That means a staff member of public health has to personally witness the patient taking their medication.

"It's rather time-intensive," Lundberg said. "You have to have staff to go and take the time to meet these people. That makes a lot of difference,"

The reason direct observation therapy is used is because missed dosages could cause the TB to develop into a form resistant to many of the antibiotics.

"It's well worth monitoring," Bhattal said of the direct observation therapy. "With that DOT, we're able to keep the rates down a little bit statistically,"

More information on TB and World TB Day can be found at www.cdc.gov/tb.

Contact Appeal-Democrat reporter Robert LaHue at 749-4713 or rlahue@appealdemocrat.com.