SAN DIEGO -- A Marine recruit died of a "bacterial infection," but investigators don't know if the death was related to an outbreak of strep A at San Diego's Marine Corps Recruit Depot, officials said Monday.

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Doctors Scrambling For Answer

Pvt. Miguel Zavala (pictured, left), 18, of Greenfield, Calif., died Sunday at Naval Medical Center San Diego after a rash on an ankle spread to much of his body.

"(Sunday's) sudden death was certainly a bacterial infection," said Navy Capt. John Malone of the Naval Medical Center San Diego, who attended Monday's autopsy.

He said there was no indication of any flesh-eating process that would point to necrotizing fasciitis -- the so-called flesh-eating bacteria -- or streptococcal toxic shock, which can result from streptococcus Group A.

With the outbreak of strep A that has sent more than 100 recruits to the hospital in the last week or so, all Marines at MCRD are being given throat cultures for the bacteria.

Fifty Marines are now in the hospital with some sort of infection, including Group A strep. One is in critical condition, apparently with an illness related to strep A, officials said.

The strep A outbreak is confined to four of the base's seven companies. All of the ill recruits arrived for training in the last 30 days.

Officials halted physical training over the weekend, and will re-evaluate the situation on Wednesday. Recruits are still marching and going to safety classes, but aren't running, swimming or doing martial arts.

Zavala's death was the third in recent weeks. The other two deaths occurred following physical training, and were not believed to be linked to the strep A outbreak.

Maj. Gen. Jan Huly, commander of MCRD, said officials are "certainly concerned."

"Mothers don't send their sons to the Marine Corps and and expect them to become casualties in recruit training," Huly said. "We take every one of those deaths personally, as if there were some way we could have prevented it, and we're going to find a way we can prevent it."

Pvt. Neal Edwards, 18, of St. Clair, Mo., died on Nov. 24 after collapsing during training on an obstacle course. Officials Monday said Edwards may have had a heart defect.

Pvt. Samuel Bruss, 19, of Kenosha, Wis., died Thursday after survival training at the base swimming pool. The cause of Bruss' death was still under investigation, but officials said his lungs were filled with fluid.

County health officials were notified about the illnesses at the recruit base, said Dr. Michele Ginsberg, head of the county health department's epidemiology unit.

"Their communication with us has been very good," Ginsberg said. "They keep us abreast of what is occurring."

Over the weekend, several thousand recruits were inoculated against the strep illness.

Strep is a common bacteria people carry in their throat, though most don't become sick, Ginsberg said. When illnesses arise, sore throat is the most common, but more serious infections also can result, she said.

"In situations where these clusters of illness occur, this is the type of setting where you would find it," Ginsberg said, referring to MCRD conditions where many people are in close quarters and "working intensely."

One sign of streptococcal toxic shock syndrome is a flat red rash over large parts of the body.

As for preventing the spread of strep illnesses, Ginsberg said hand washing is important, as is covering sneezes and coughs, and disposing of tissues.