New research suggests that an outbreak of wound and bloodstream infections among U.S. service members in Iraq was acquired at contaminated field hospitals, not on the battlefield.

Army doctors noticed an increasing problem of infection with a drug-resistant microbe called Acinetobacter baumannii-calcoaceticus complex (ABC) among casualties being treated in Iraq.

Acinetobacter bacteria are found in soil and water but usually cause no problem. In fact, it's quite common for people to carry the germ on their skin without any ill effects. However, with open wounds and reduced immunity there's an increased risk of ABC infections.

Dr. Paul Scott, from Walter Reed Army Institute of Research in Rockville, Maryland, and colleagues looked into ABC infections seen in wounded soldiers evacuated from Iraq, and examined three possible sources for infection.

Skin samples from 160 soldiers were tested for the presence of ABC bacteria. In addition, samples from the soil and from healthcare environments were also examined for evidence of the microbes.

Just one of the patients tested had evidence of ABC on the skin, the team reports in the journal Clinical Infectious Diseases, and only 1 of 49 soil samples carried the microbes. By contrast, ABC bacteria were present in samples obtained from all seven field hospitals studied.

Taken together, these findings suggest that drug-resistant ABC infection was not acquired in the battlefield, but only after the patients had been treated for wounds at field hospitals.

The results of a second study, which is reported in the journal Infection Control and Hospital Epidemiology, also point to contaminated field hospitals as being the source of these outbreaks.

"We need to know where these infections are coming from," Dr. Matthew E. Griffith said in a statement. "One of the possibilities was that ABC was on the soldiers' skin before injury and simply traveled to the wound site to cause the infection. "

The study involved skin testing of 102 active military soldiers stationed in Iraq.

Contrary to what had been expected, Griffith, from Brooke Army Medical Center at Fort Sam Houston in San Antonio, Texas, and colleagues found that uninjured soldiers in Iraq do not carry drug-resistant ABC on their skin.

If the organism was not present on the skin before injury, then it is likely to have come from some other source and entered the wound after injury, Dr. Griffith said. One likely source: field hospitals.

These findings add "to the ever growing body of evidence" implicating health care-related transmission as the cause of the ongoing military ABC outbreak.

SOURCES: Clinical Infectious Diseases, June 15, 2007; Infection Control and Hospital Epidemiology, May 16, 2007