U.S. soldiers returning with resistant Acinetobacter baumannii infections

November 2005

SAN FRANCISCO – Drug-resistant Acinetobacter baumannii, carried by U.S. soldiers returning from Iraq and Afghanistan, is emerging as a potentially serious problem in U.S. hospitals, according to reports from the 43rd Annual Meeting of the Infectious Diseases Society of America (IDSA).

“In March of 2003, an outbreak was noted that involved combat causalities returning from Operation Iraqi Freedom at several hospitals in the U.S. military medical evacuation route, which begins in Iraq and typically goes through Europe and Germany, and then on to the United States,” said Paul T. Scott, MD, chief of epidemiology and threat assessment, division of retrovirology at Walter Reed Army Institute of Research in Washington. Scott and colleagues did a two-phase epidemiological investigation.

“The outbreak was quickly confirmed using the surveillance network data where 1% to 2% of all wound infections in U.S. hospitals are Acinetobacter,” he said.

Between March and September 2003, military physicians were seeing between one and three cases per day, according to Scott.

“All of these patients in the initial outbreak were severely wounded combat casualties who had either limb or life-saving surgery at field hospitals in Iraq before their evacuation and they were mostly … young males,” he explained.

About 7% of isolates were not sensitive to any of the standard antibiotics, 26% were sensitive to carbapenem only and an additional 23% were sensitive to carbapenem and one other drug class.

For treating patients, only two antibiotics, imipenem and amikacin, were effective against the bacterium more than half of the time. In fewer than 10% of cases, only imipenem was effective, according to Scott.

More than 250 patients, mostly soldiers who served in the Middle East, have been identified in this outbreak. Not all the cases occurred in military personal. Civilian patients who were very ill and receiving treatment in military hospitals were also infected, and five have died as a result of the infection. No military personnel who served in the Middle East have died of the infection.

Acinetobacter is commonly found in soil and water, and because the infections occurred mostly in healthy young soldiers who had been wounded, researchers originally believed the victims were exposed to the bacterium when bits of dirt embedded in their wounds.

“This gram-negative bacterium is present worldwide in water and soil and is found to cause infections in every part of the body and it’s strongly associated with outbreaks of nosocomial disease in critical care centers,” Scott said.

Scott and colleagues tracked infections in 148 people, most of whom were active duty soldiers wounded by land minds, mortar fire or bombs.

All 148 had been treated in one or more of the following facilities: Walter Reed Army Medical Center, Washington; Landstuhl Regional Medical Center, Germany; the USS Comfort; or a field hospital in Iraq.

Bacterium-related illnesses

The bacterium led to various illnesses, including infections in wounds, blood, the respiratory and urinary tracts. Most of the patients had fever, which typically lasted a week, stayed in the hospital for an average of 39 days and were prescribed antibiotic therapy for an average of 29 days.

The researchers collected samples in and around the field hospitals in Iraq and Kuwait to characterize the soil ecology and see if they could find any samples that were clinically significant.

“We collected 170 isolates from 148 patients, and this was able to give us an opportunity to track outbreak strains because these were collected at multiple locations of treatment per person and from four different facilities, one in Iraq and one at a hospital ship in the Persian Gulf and then one in Germany and one in the United States,” he said.

“We recovered 37 Acinetobacter isolates as a result of the sampling and most were recovered in our critical care treatment areas,” he continued.

He said the researchers recovered many samples on equipment, such as the environmental and control unit machine and operating room tables and lights.

The also collected 31 soil samples, but were unable to isolate Acinetobacter in the soil.

Finally, the researchers did a retrospective cohort study of inpatients treated at Walter Reed only to see if there was any clinical significance to these infections.

They identified 96 patients who met the inclusion criteria.

“At the end of phase 2, our findings were that this appeared to be in fact a hospital-associated outbreak throughout the military health care system. Of those 96 patients I just showed you, 18 of them represented cross infections and we were able to establish pulse field studies on our environmental samples and clinical samples with a direct link as far back as to our treatment areas and our field hospitals,” he said. Scott’s research suggests that Acinetobacter actually is acquired in the hospital. Scott said that investigators still do not know how the field hospitals became contaminated.

Infections caused by Acinetobacter have long been a problem in European and Israeli hospitals, but prior to Operation Iraqi Freedom, A. baumannii was rarely seen in U.S. military hospitals. There has also been a rise in Acinetobacter infections in this country outside of the military setting, including two outbreaks in U.S. hospitals.

Treatment options

Acinetobacter has been around for a long time but appears to have become more drug resistant.

It was one of the most common causes of infection during the Vietnam War and at that time it did not appear to be resistant to antibiotics, according to Scott.

Lt. Cmdr. Kyle Peterson, MD, National Naval Medical Center, Bethesda, Md., discussed the outbreaks in a different presentation at IDSA, and reviewed the data from Vietnam in 1972. In one study, Myron Tong, MD, PhD looked at 30 patients who had 63 extremity wounds, and found Acinetobacter accounted for about one-third of the infections. Peterson said the wounds were “very similar to what our Marines are having in our hospital right now.”

Although the gram-negatives appeared to have dominated in Vietnam, as they are in Iraq, the difference was antibiotic resistance.

“We’ve got massive amounts of gram-negative resistance, and I cannot explain why that is in the particular area where we’re seeing our injuries from unless the Iraqis were using a lot of antibiotics in their hospitals and it just got into the soil. I do not think that they were using it in their agriculture, but that remains to be a big question,” Peterson said.

He discussed the response at Walter Reed to control this infection.

“We’ve been aggressively screening everybody who comes back with swabs of their groin, axilla and nares on arrival to the hospital from the medivaced flight and we’ve now collected 567 wounded-in-action admissions in our database … about a third are positive for Acinetobacter and about 10% of them are true infections with about the other 90% being colonized,” he said.

Walter Reed officials have also instituted isolation policies and universal precautions, such as wearing gowns, gloves and masks around positive patients, regardless of who the visitor is, he said.

He mentioned that many people, from politicians to Miss Maryland, have expressed interest in visiting the soldiers in the hospital. They all must practice infection control, he said.

Hand washing is very important. “Of paramount importance is enforcing hand washing among our employees because … it would be very easy to grow off of people’s hands,” he said.

He said the organism is difficult to eradicate in the environment.

“The persistence has been shown … to be up to 176 days and high-level decontamination has to be done once you get it into the hospital rooms because it gets on surfaces and sticks around for a few days, and it’s very hard to eliminate. You have to wash curtains, scrub everything down with bleach, basically shut down your unit and have a high-level field day to get it,” he said.

The U.S.S. Comfort had a serious problem with the organism that was nearly impossible to eliminate. “We had a big problem with this and I think our problem was that we didn’t have any hand hygiene products and there was no impetus ahead of time to think about things like this when the ship was designed. We had one sink for every ward of 70 beds. There was a shortage of gowns,” he said.

“We did finally just shut down whole wards at a time and make them dirty. You put all your dirty [infected] patients in there, but the problem was that, basically, I was getting a phone call from the lab everyday when I had a positive isolate and then I was putting them into isolation after that, and they were probably infected and sitting on the ward for several days ahead of time spreading it to other patients. We never really did catch up until we medivaced everybody back to Iraq,” Peterson said.

Peterson said because the organism is multidrug resistant, one probably wants to start with two drugs initially. Débridement of infected tissue may also be necessary.

For more information:

• Peterson K, Aronson N. Infections in returning soldiers. Meet the Professor Session #120.
• Scott P, Hulten E, Craft DW, et al. An outbreak of multi-drug resistant Acinetobacter baumannii infections in the military health care system associated with Operation Iraqi freedom. Abstract #327.
• Both presented at the 43rd Annual Meeting of the Infectious Diseases Society of America. Oct. 6-9, 2005. San Francisco.