SCCM - Society of Critical Care Medicine

Fighting a Different Enemy: Infections and Combat-Related Injuries

Clinton K. Murray, MD*
Infectious Disease Service
San Antonio Military Medical Center
Brooke Army Medical Center
Fort Sam Houston, Texas, USA

Duane R. Hospenthal, MD, PhD**
Infectious Disease Service
San Antonio Military Medical Center
Brooke Army Medical Center
Fort Sam Houston, Texas, USA

Read a related article in Critical Care Medicine.
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Current strategies to mitigate excess morbidity and mortality associated with combat-related injuries include improving personal protective equipment (e.g., body armor), locating surgical assets nearer to the point of injury, evacuating casualties rapidly for medical care, and enhancing training for combat medics and corpsmen. These interventions have resulted in remarkable survival rates during combat operations in Iraq and Afghanistan (Operation Iraqi Freedom [OIF] and Operation Enduring Freedom [OEF], respectively). (1) The wounding patterns during OIF and OEF are similar to those seen in prior wars, with approximately 55% of casualties suffering extremity injuries.

While there have been more head and neck injuries (30%) during OIF/OEF compared with the Vietnam (16%) and Korean (21%) wars, a remarkable decrease in thoracic injuries has been noted (6% in OIF/OEF compared to 13% and 10% in the Vietnam and Korean wars, respectively). (2,3) Despite these changes in wound patterns and the improved strategies to mitigate excess morbidity and mortality rates, infection remains a major cause of morbidity and mortality, with sepsis being the fourth most common cause of potentially reversible mortality. (4) Approximately one-third of casualties from OIF/OEF develop an infectious complication. These typically include infections of the skin, wound or lung caused by Gram-negative pathogens. (5) Casualties who sustain more severe injuries, particularly those due to explosive mechanisms, are at higher risk for infections.

Infections with Multidrug-Resistant Pathogens
Since the onset of military operations, physicians within military healthcare facilities both in and out of the combat zone have been dealing with casualties who have developed infections with multidrug-resistant (MDR) bacteria, notably Acinetobacter baumannii-calcoaceticus complex. (6,7) This pathogen is remarkable because it has not been seen previously with any regularity at military healthcare facilities in the United States, and it was not recognized as a common pathogen in previous U.S. wars. (8) Interestingly, Acinetobacter was noted during the Iran-Iraq War in casualties who suffered central nervous system injuries, but it was not associated with attributable morbidity or mortality. (9,10) Although the virulence of this pathogen has been debated in the current war, there may be host or strain variability associated with excess disease and easier transmission. (11-17) The broad spectrum of antimicrobial resistance that these organisms possess or acquire is of great concern. (18) Other pathogens, including extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae and Escherichia coli, as well as Pseudomonas aeruginosa, also have been reported in combat-related injuries. (14,16) In contrast to Acinetobacter, some of these pathogens have been associated with excess morbidity and mortality rates. Methicillin-resistant Staphylococcus aureus (MRSA) also has been seen among casualties, especially among those with extremity injuries that became infected and who subsequently relapsed, notably when prosthetic material was present. (16)

Source of MDR Pathogens
Early priorities for controlling infections from these MDR bacteria were to determine if the inoculation of bacteria into the wounds occurred through environmental contamination at the time of injury, through colonization of the patient prior to injury, or through nosocomial transmission. For certain pathogens, such as MRSA, all three modes of inoculation have been associated with combat-related injury infections. (19,20) For other pathogens, especially Acinetobacter, studies were conducted in and out of the combat zone to determine how they were acquired, as this could have substantial impact on infection control strategies and antibiotic therapy. (20-23) In the case of Acinetobacter, primary data indicate that most incidences were the result of nosocomial transmission in and out of Iraq and Afghanistan; they were not caused by prior colonization or inoculated into the wound at injury. These findings are consistent with non-military data that indicate MDR bacteria may be transferred during the international air evacuation of injured travelers or through the movement of patients between regional hospitals. (24,25)

It is unclear how these MDR bacteria first became introduced into the military healthcare system. Researchers have hypothesized that drug pressure may have selected these pathogens or that there was cross-contamination from hospitals in the Middle East, as these hospitals had high rates of MDR Gram-negative bacteria at the beginning of OIF/OEF. The introduction also could have been caused by increased rates of MDR pathogens in trauma victims, as noted with those injured during earthquakes and tsunamis, many of whom developed Acinetobacter infections. (26-29)

Response to MDR Pathogens
Nosocomial transmission appears to play a major role in the propagation of these MDR, so emphasis has been placed on improved infection control strategies to stop the spread of these bacteria. Data suggest that non-U.S. patients in deployed U.S. military hospitals may serve as a bacterial reservoir. (30) Rapid discharge of these patients to host-nation healthcare facilities has been shown to decrease the presence of Acinetobacter within a combat surgical hospital. (31) In addition, data show pulmonary colonization and/or infection as an early site of recovery of MDR pathogens and thus a potential target of increased infection control emphasis. (32) This is relevant, as a program to reduce ventilator-associated pneumonia (VAP) rates in a deployed U.S. hospital in Iraq (established in tents with frequent mass-casualty events) was successful. VAP rates fell to levels equal to those of trauma intensive care units in the United States. (33) Interventions included standard infection control techniques used in the United States, such as collecting data, improving hand hygiene, isolating and cohorting patients, and minimizing the duration and spectrum of antibiotics. As an added benefit, bacteria within the facility became nearly 25% less antimicrobial resistant.

In contrast to the care of trauma patients in the United States, OIF/OEF casualties with combat-related injuries are managed by a global military healthcare system. Patients travel to an average of four medical facilities from the point of injury back to U.S.-based hospitals, typically located in Washington, DC, or San Antonio, Texas. (15,21) This evacuation process takes an average of seven days and spans nearly 7,500 miles, resulting in the application of many infection control, surgical and antibiotic management strategies.

To address infectious complications in patients with combat injuries, evidence-based reviews of the medical literature and practice guidelines have been produced. (34) A consensus conference held in June 2007 brought together military and civilian experts who had served in every aspect of care within the military healthcare system from point of injury to chronic rehabilitative care (including several who had served during the Vietnam War). Professionals included infectious disease physicians, preventive medicine and infection control experts, and surgeons with expertise in trauma and general surgery as well as professionals with intensive care, burn, central nervous system, orthopedics, and head and neck injury expertise. A summary document was produced along with evidence-based support for recommendations, which were divided into extremity injuries, central nervous system injuries, head and neck injuries, thoracic and abdominal injuries, and burn injuries. (35-39)

Combat-related injuries during military operations in Iraq and Afghanistan have been associated with infectious complications due to MDR bacterial pathogens, especially Gram-negative bacteria. Investigations are underway to identify the source of these bacteria and to try to mitigate their associated morbidity and mortality. As in the U.S. civilian medical community, new antimicrobial agents are needed to treat these infections. Platforms to identify infection and its antimicrobial resistance profile also are needed to ensure appropriately focused therapy is instituted.

References

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37. Conger NG, et al. Prevention and management of infections associated with combat-related thoracic and abdominal cavity injuries. J Trauma. 2008;64(3 Suppl):S257-264.

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39. D’Avignon LC, et al. Prevention and management of infections associated with burns in the combat casualty. J Trauma. 2008;64(3 Suppl):S277-286.

Disclosures

*Author has no disclosures to report.

**Author has no disclosures to report.