40 Bacteriology and Causes of Recurrent Bacteremia in Combat Burn Casualties

Abstract

Bacteremia is a risk factor for increased mortality in combat burn casualties. Surviving the first episode of bacteremia predisposes burn casualties to recurrent bacteremia. However, very little is known of the incidence of recurrent bacteremia in burn casualties. Herein, we investigate bacteriology, predictors, and mortality of recurrent bacteremia in combat burn casualties admitted to our Burn Center over a 10 year period from March to Dec 2013. The microbiological database was queried for results of blood cultures, bronchoalvelolar lavage fluid, stool, urine, and wound cultures. Bacteremia was defined as the growth of Gram-positive or Gram-negative organisms in blood culture that excluded coagulase-negative staphylococci, Corynebacterium spp., and Propionibacterium spp. as probable contaminants. Recurrent bacteremia was a subsequent episode of bacteremia ≥ 7 days after the first episode. Polymicrobial bacteremia was the presence of more than one pathogen in the same blood culture. Bacteremia was attributed to UTI, Pneumonia, or Wound Sepsis determined per criteria defined by the CDC. All other bacteremia was considered Non-attributable Bloodstream Infection (NABSI). Univariate and multivariate analysis was done to determine factors predictive of clinical outcome (p ≤ 0.05). Of the 166 casualties meeting inclusion criteria, 63% had non-recurrent bacteremia and 37% had recurrent bacteremia with a median time to recurrence of 20 days. In both groups, Gram-negative organisms were the predominant causative pathogen. Acinetobacter baumannii complex (63%) was the most prevalent in the non-recurrent group, while K. pneumoniae 46% vs. 30%) and P. aeruginosa (35% vs. 26%) were more common in recurrent bacteremia. Half of the recurrent bacteremia cases were polymicrobial compared to 8% in non-recurrent bacteremia. NABSI (~40%) was common in both groups. Of those with identified sources, pneumonia was most common in non-recurrent bacteremia (38%), and a combination of wound sepsis and pneumonia (29%) in recurrent bacteremia. Mortality rate was two-fold higher in recurrent bacteremia patients. Univariate analysis indicated TBSA, ISS, and recurrent bacteremia as risk factors for mortality. Multivariate analysis demonstrated only recurrent bacteremia to be independently associated with mortality. Recurrent bacteremia is associated with virulent Gram-negative organisms and polymicrobial bacteremia. The higher mortality is multifactorial and maybe due to the immune-compromised status of combat burn casualties. Understanding the bacteriology and the sources of infection would enable development of strategies to prevent as well as treat bacteremia, which could reduce mortality in combat burn casualties.