Acinetobacter Baumannii Infections in Hospitals

The bacterium Acinetobacter Baumannii saw a sudden emergence in military treatment facilities during the Iraq War, earning it the colloquial name Iraqibacter. Since the conclusion of the war, it has been a persistent problem among veterans and soldiers. The transport of soldiers through multiple medical facilities has increased the spread of the bacteria in civilian hospitals. Multi-drug resistant and not well studied, it has been identified as an ESKAPE pathogen, meaning it is responsible for a majority of nosocomial (hospital-acquired) infections. Few antibiotics are effective in the treatment of this pathogen, and further study is required to effectively combat its spread and fight existing infections. A cousin of the bacteria is found commonly in soil, leading to the misconception that A.baumannii is a soil-dwelling organism as well. Almost exclusively, it is isolated from health care settings.

Certain virulence factors have allowed A.baumannii to excel as a pathogen, with efficacious toxin delivery systems that burden and wear down the host cell. Its overall microbial fitness allows it to withstand the environment of the host, without affecting the host directly or perceptibly. Specific genes, called pathogenicity islands, increase virulence by encoding toxins, coagulating blood of the host or allowing antibiotic resistance. Horizontal gene transfer allows a bacterium to take up new genetic material, integrating it into the organism's genome.

A.baumanni is notable in its ability to form biofilms, allowing it to survive on hospital surfaces for long periods. After forming a biofilm, the microorganism's metabolism is affected and they are consequently less sensitive to antibiotics.

Infections have been documented in the US, the UK, Australia, China, Brazil, India, South Korea and Germany.

Causes of A.baumanni Infections

Infection in soldiers and veterans is due, in part, to their frequent transfer between facilities after injury. As A.baumanni is rarely isolated from the environment, the infection does not occur at the time of injury. Rather, it is sustained after the soldier is transported to a medical environment, where the bacteria is prevalent (the only place in which it is prevalent.) Equipped with the ability to survive on surfaces for an extended period, it is thought that soldiers are exposed to the bacteria during the casualty-evacuation process. Back and forth transfer between level-I and level-II facilities is common, prior to being transferred to a level-III facility in a combat zone. This could be followed by transfer to a regional facility after service has concluded (such as hospitals in Europe on their way to their home country.) This concludes with a transfer to a medical facility in their home country. Researchers have identified this frequent transfer as a chief reason behind increasingly common A. baumanni infections. Infection with this multi-drug resistant pathogen has the potential to complicate treatment for returning soldiers and can increase mortality from underlying injuries, diseases or conditions.

A. baumanni is one of many opportunistic bacteria which take hold of patients with compromised immune systems, diabetes, chronic lung conditions, urinary or intravenous catheters and open wounds. Transmission occurs via contact with contaminated surfaces and skin to skin contact with contaminated individuals. Researchers suspect the bacteria favors hospital environments because of the prevalent use of antibiotics, which create host environments in which there is less microbial competition. In one study, approximately, 20% of VAP cases (ventilator associated pneumonia) was caused by A.baumonni.

At least one study showed that body lice is another important reservoir for the pathogen, as it was recovered from 22% of homeless individual's body lice samples.

Symptoms of A.baumanni Infections

Like other opportunistic bacteria found in hospitals, the symptoms of infection are conditions in and of themselves. Each condition caused by this bacterial infection is accompanied by a different set of associated symptoms, therefore symptoms are dependent on the area of the body which the bacteria infect.

These conditions are not unique to A.baumanni and can include:

  • Pneumonia
  • Meningitis
  • Bloodstream Infections (bacteremia)
  • UTI
  • Flesh eating infections

In some cases, the bacteria can colonize a wound or tracheostomy site without causing symptoms. Like a handful of other pathogenic bacteria, the presence of A.baumanni in a culture from sputum or respiratory secretions is not definitive evidence of infection, and it may be difficult to interpret whether the bacteria is infecting the individual or has simply colonized without issue.

Risk Factors for A. baumanni Infection

As the chief source of infection among injured soldiers, deployment and military service itself are risk factors for infection. Transfer between multiple medical facilities places both civilians and military personnel at greater risk. Those with weakened immune systems are a particularly high-risk group. Patients who spend a great deal of time in ICUs or have prolonged hospital stays are also at greater risk. Like other opportunistic bacterial infections, the risk of infection is greater for those who have catheters, sutures, ventilators and those who have undergone dialysis or antimicrobial therapy

Treatment of A.baumanni Infections

Many facets of this pathogen make it especially difficult to treat. A comparative lack of scientific literature regarding the bacteria makes it more difficult to fully understand its mechanisms of growth and antibiotic resistance. Knowledge of its pathogenesis could help researchers to develop more effective and numerous treatment options.

Due to a considerable multidrug resistance and the desire to reduce the acquisition of further antibiotic resistance in the species, it is critical for health care providers to determine particular antibiotic susceptibilities (weaknesses) of the strain infecting the individual. Carbapenem class antibiotics have been effective, although resistance within the species seems to be on the rise. Pandrug resistant strains have arisen as a result of the bacteria's ability to deftly acclimatize itself to the environmental pressures forced upon it by antibiotics. For this reason, the last resort antibiotic colistin is sometimes used, although it is considered a last resort antibiotic which can cause kidney damage and other potential side effects.

Prevention of A. baumanni Infections

As stated, A.baumanni does not differ on many counts from other opportunistic pathogens, aside from its competent adaptability to various environmental stressors. Therefore, methods of prevention are similar to those employed to control the spread of any other opportunistic bacterial pathogen. These measures include fastidious hand hygiene and surface sterilization prior to handling patients with susceptible conditions. Wounds should be kept clean and covered and antibiotic courses should be used sparingly and only when absolutely necessary. When used, it should be ensured that the patient sees them through to completion. This may be achieved with direction observational therapy.

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