Los Angeles County health officials have asked for federal assistance to analyze and contain an outbreak of tuberculosis within the city's homeless population, a spokeswoman for the county agency said on Friday.
Los Angeles County Health Department spokeswoman Mabel Aragon said the agency is still in the process of confirming the number and type of TB cases in the county.
"The CDC is helping us with surveillance and statistic gathering," she said.
CDC spokesman Scott Bryan confirmed that the federal health agency has been asked by local and state TB officials to assist with the outbreak investigation. Bryan said the CDC plans to dispatch staff to the state in the next two weeks.
The Los Angeles Times reported that health workers have identified about 4,650 people who were probably exposed to a persistent outbreak of the contagious disease on downtown Los Angeles' skid row.
The newspaper said that over the past five years, county officials have identified 78 cases of a unique strain of the contagious disease, including 11 deaths. Sixty of those cases were homeless individuals leaving in the skid row area.
In an interview posted on the Los Angeles health department's website, Kiren Mitruka of the U.S. Centers for Disease Control and Prevention said: "Although progress has been made toward eliminating TB in the U.S., TB outbreaks continue to occur and remain a challenging issue."
The United States had about 10,528 cases of tuberculosis in 2011 and there were 529 deaths from the disease in 2009, according to the latest full year CDC statistics.
The CDC responds to TB outbreaks only when state and public health departments exceed their surge capacity to control it, Mitruka said.
"We don't go in unless we're asked," she said in the online interview.
Typically, the CDC will conduct an onsite investigation lasting two to three weeks, working closely with state and local public health partners, Mitruka added.
The cluster of TB cases going on in Los Angeles follows a pattern of infection. A review of 51 TB cases which the CDC investigated between 2002 and 2008 published in Emerging Infectious Diseases found substance abuse was the most common risk factor, with 58 percent of outbreak patients reporting substance abuse.
Tuberculosis infection destroys lung tissue, causing patients to cough up the bacteria which then spreads through the air and can be inhaled by others.
Most cases can be cured with a six-month cocktail of antibiotics, but rates of drug-resistant TB have been spreading fast, causing alarm among public health officials and prompting calls for more research into new treatments.
"I think it's a wakeup call that highlights the fact that this is still a major, major problem," said Dr Mel Spigelman, chief executive of the TB Alliance, a nonprofit research group based in New York.
"Even in the U.S., where we have one of the lowest rates in the world, we still have over 10,000 patients every year who get TB."
Spigelman said that number pales in comparison to the 9 million people globally who get TB.
"It's still in the U.S., we just don't recognize it."
(This story corrects spelling of TB Alliance chief executive's last name to Spigelman, not Spiegelman, fourth paragraph from bottom)
(Reporting by Deena Beasley and Julie Steenhuysen; editing by G Crosse)