County health officials say there is a public health threat in the valley right out of the 19th century -- tuberculosis.

The illness once known as consumption is more common in Napa County residents than more publicized diseases like West Nile virus. On average there are three to six cases of tuberculosis in Napa County each year, while officials have yet to identify a human case of West Nile.

County health officials say the presence of tuberculosis in the county is largely due to an influx of immigrants from developing countries, where the disease is more common than in the United States. Officials say undocumented immigrants add to the risk because they do not undergo testing for tuberculosis at border entry points, as their legal brethren do.

American Lung Association data shows California reports the highest rates of tuberculosis infection in the nation. In 2005, there were 7.9 cases of tuberculosis per 100,000 residents. The American Lung Association estimates 3.6 million Californians are infected with latent tuberculosis, which can lie dormant for decades before age or illness weakens the immune system and the bacteria that cause full-blown tuberculosis begin to multiply.

But take heart before casting a wary eye to the person coughing next to you in line at the grocery store -- you can't catch tuberculosis from short periods of contact with sick people.

"To acquire tuberculosis from someone it takes sustained contact," said Dr. Karen Smith, Napa County public health officer. "You're not going to get it from someone coughing on a bus. The people most at risk of TB are (infected people's) family members."

Nonetheless, what has been called one of history's most deadly diseases should be on local physicians' radars, and is regularly screened for at Clinic Ole, which serves low-income and some uninsured residents.

Smith said doctors need to be on the lookout for tuberculosis in patients they might normally pass off as having common pneumonia.

"We want to maintain a fairly elevated level of concern so that those folks with TB get treated promptly," Smith said.

According to the Centers for Disease Control, tuberculosis is caused by microscopic bacteria that can attack any part of the body, like the kidney, spine and brain, but is more common as a disease of the lungs.

It's when the lungs are attacked that tuberculosis can be spread through the air by infected people talking or coughing.

Dr. Robert Moore, medical director of Clinic Ole, said some of the signs of tuberculosis are a cough that has lasted longer than three weeks accompanied by weight loss, night sweats or coughing up blood.

Scientists discovered what became the first of a few medicines that could treat tuberculosis in the 1940s, slowly decreasing the incidence of the disease in the United States until the late 1970s and early 1980s, when government programs to monitor tuberculosis were cut. The CDC said tuberculosis resurged between 1985 and 1992.

"One key factor was that because people no longer thought it was a problem, TB screening programs were dropped throughout the country," Smith said. "The other factor is that people were de-institutionalized and became homeless. The homeless are particularly susceptible to TB ... at the same time HIV came out and there is no more important risk factor for developing TB than HIV. (HIV) suppresses the immune system."

According to the World Health Organization, tuberculosis kills 5,000 people a day, mostly in the developing world -- and a new, rare form of the disease that is resistant to modern drugs is drawing concern among some physicians.

Yet $400,000 in funding for state programs to control tuberculosis were cut during the state budget crisis five years ago and have remained out of the budget.

Barbara Cole, director of disease control for Riverside County and chair of the state's tuberculosis technical advisory board, said apathy about tuberculosis stems from its perception as a thing of the past.

"One of the things we want to promote is restoration of the funds that were cut and looking at how California represents a high proportion of the cases that were reported," she said.

"There is still lots of work to be done to move toward controlling TB -- much less eliminating it."