Alison Young

USA TODAY

The Senate's homeland security committee, citing reporting by USA TODAY, wants answers from three federal agencies about their handling of an ongoing investigation of the risks posed by the recent release of a deadly bioterror bacteria from a laboratory in Louisiana, according to letters sent Wednesday.

Understanding how the bacteria got out of a high-security lab at the Tulane National Primate Research Center near New Orleans is "imperative" because of the potential bioterrorism threat posed by the organism, said the letters signed by committee chairman Sen. Ron Johnson, R-Wis., and ranking Democratic Sen. Thomas Carper of Delaware. The letters were sent to top officials at the Centers for Disease Control and Prevention, the U.S. Department of Agriculture and the Environmental Protection Agency.

The senators note that the Tulane accident follows other "concerning reports" of incidents at federal labs and as the country has faced potential threats from infectious diseases ranging from measles to avian influenza and Ebola.

"These events are reminders as to how vulnerable our nation may be to a serious biological incident," the letters said. "Our committee takes seriously our oversight responsibilities in how federal agencies are working to prepare for and respond to these potential threats to our national security." Johnson and Carper could not be reached for comment.

For weeks, federal officials have been investigating how a deadly, foreign bacterium called Burkholderia pseudomallei got out of a high-security lab on the 500-acre primate center campus, sickening three monkeys not involved in any experiments. CDC investigators recently concluded that the bacteria probably were carried out of the lab on the clothing of workers using sloppy biosafety practices.

The incident has raised concerns that the bacteria may have contaminated soil or water in the facility's large outdoor primate breeding colony of about 5,000 rhesus macaque monkeys. The first sign that the bacteria had escaped Tulane's biosafety level 3 lab was the identification of two ill monkeys that were housed in separate outdoor cages. The bacterium is not found in the United States, the CDC has said, but is most commonly found in soil and water in Southeast Asia and northern Australia. Ill monkeys can shed the bacteria in urine and feces, officials have said. People and animals can be sickened by the bacteria if they come into contact with contaminated soil or water.

The CDC has said it is unlikely there is any threat to the general population, but the investigation is ongoing.

Tulane officials have said they don't believe the bacteria have ever gotten outdoors and have pointed to soil testing coordinated by the U.S. Environmental Protection Agency that didn't detect the bacteria. The committee wants the EPA to explain the "scientific justification for the soil sampling plan ... particularly as it pertains to the number of soil samples taken at the site."

The letter cites USA TODAY's reporting that found only 39 soil samples were tested — far too few to detect the elusive bacteria if present. The newspaper reported that in parts of the world where the bacteria has lived for decades, studies have found it is difficult to detect without a large number of samples because it forms underground colonies like invisible ant hills that aren't evenly distributed across an area.

The senators also want to know more about the agencies' efforts to determine whether soil and water conditions near the lab could support colonization of the bacteria, as well as the status of plans to monitor wildlife and domestic animals in the vicinity for signs of exposure. Other questions seek to examine how the agencies have coordinated their investigation. The letters set an April 8 deadline for the agencies to respond.

EPA and USDA officials could not immediately be reached.

"I think that Congress understands how important the work at Tulane and other institutions is across the country, but they've raised concerns that this work is not being done safely," CDC spokesman Tom Skinner said Wednesday evening. "CDC concurs that this work must be done safely and we will be responding to the senators' letter accordingly."

Read the letters sent by the committee to the CDC, the EPA and the USDA.

For full coverage of the Tulane lab incident and other safety and security issues at U.S. labs, go to: biolabs.usatoday.com

Follow USA TODAY investigative reporter Alison Young on Twitter: @alisonannyoung