Eleven Southern California counties and 13 public health agencies will take part in the state’s largest bioterrorism drill starting Monday and continuing through the week, officials say.

The event, called the Southern California Regional Exercise for Anthrax Disaster Incidents, or SoCal READI, includes members of state and county public health agencies, hospitals, elements of law enforcement, hospitals and many volunteers in a practice response to a simulated large-scale aerosolized anthrax bioterrorism attack, said Susan Fanelli, assistant director of the California Department of Public Health.

The bacteria that causes anthrax would be one of the biological agents most likely used in a bioterror attack, according to the Centers for Disease Control and Prevention. Inhaled anthrax is the most deadly form of the disease, with survival rates of only 10 to 15 percent, increasing to 55 percent with aggressive treatment, the agency’s website says.

SoCal READI has been in the planning stage for two years and builds on smaller drills conducted across the state in the years since the terrorist attacks of Sept. 11, 2001, Fanelli said

Following the attacks on the Pentagon and the World Trade Center, California received federal funds for emergency planning, and some of those resources were used for developing bioterrorism protection plans, Fanelli said.

Counties participating include San Bernardino, Riverside, Los Angeles, Orange, San Diego, Imperial, Inyo, Mono, Ventura, San Luis Obispo and Santa Barbara. The health departments from the cities of Long Beach and Pasadena are also participating,

Each county and health agency will determine its participation for the practice drills, Fanelli said.

The mock attack will occur on Monday over a vast Southern California area, officials said.

By Tuesday, hospitals and other organizations will “realize” that the region is in the early stage of a regional anthrax outbreak.

Much of the exercise is to practice large-scale distribution and dispensing of medications initially to first-responders and later to members of the public, officials said.

While in a real scenario antibiotics would be distributed, for the drill, candy or another placebo will be passed out. And, in a few locations, flu shots will be dispensed, officials said.

Los Angeles County Health officials could not immediately be reached for comment.

Among those participating San Bernardino County departments are public health, fire hazmat, sheriff, Office of Emergency Services and Inland Counties Emergency Medical Agency, which also includes Inyo amd Mono counties.

The exercise will also include San Bernardino county’s 18 acute-care hospitals, plus several volunteer organizations, cities and school districts, said Claudia Doyle, spokeswoman for the San Bernardino County Department of Public Health.

One of the strengths of the exercises is that it brought health department executives from 13 agencies together for joint planning activities, said Fanelli, who prior to her post in the state health department was deputy director of the Emergency Preparedness Office. The large-scale cooperative skills learned from planning for the event could be translated to a real disaster of natural or man-made origin.

“The exercises basic goal is to test the county’s response to activate emergency plans, use redundant communications and coordinate receiving and distributing medications and other medical resources within the county,” Doyle said.

Shortly after the terrorist attacks of 9-11, letters laced with anthrax began appearing in the U.S. mail. Five Americans were killed and 17 were sickened in what became the worst biological attacks in U.S. history, says the FBI’s website.

The investigation, code-named “Amerithrax,” that followed by the FBI, U.S. Postal Inspection Service and other agencies, was one of the “largest and most complex in the history of law enforcement,” the FBI website says.

In 2010, the FBI and its partners announced that U.S. Army Biologist Bruce Ivins acted alone in planning and executing the attacks. Ivins committed suicide before federal officials could file charges, the FBI website says.

The deadliest incident with aerosolized anthrax occurred at a Russian military biology facility in 1979. Of the 79 cases reported, 68 were fatal, says the Johns Hopkins Bloomberg School of Public Health website.

“Inhalation anthrax starts primarily in the lymph nodes in the chest before spreading throughout the rest of the body where it ultimately causes severe breathing problems and shock,” according to the CDC website.