In critically ill patients who were mechanically ventilated, variation in lung microbiota at admission predicted intensive care unit (ICU) outcomes, according to study results published in the American Journal of Respiratory and Critical Care Medicine.

Culture-independent microbiology have revealed that the lungs harbor complex and dynamic communities of bacteria and that the burden of lung bacteria predicts mortality and disease progression in certain patients. For example, the lung microbiota of critically ill patients are profoundly altered compared with healthy individuals and correlate with alveolar inflammation; however, the clinical significance in critical illness is unknown.

Therefore, researchers sought to determine whether lung microbiome (bacterial burden, diversity, and community composition) at ICU admission predicted clinical outcomes in 91 critically ill patients. The researchers found that patients with increased lung bacterial burden had fewer ventilator-free days, which remained significant when controlled for pneumonia and severity of illness (hazard ratio, 0.43; 95% CI, 0.21-0.88; P =.022). In addition, the community composition of lung bacteria predicted ventilator-free days (P =.003) driven by the presence of gut-associated bacteria (eg, Lachnospiraceae and Enterobacteriaceae spp.). The detection of gut-associated bacteria was also associated with the presence of acute respiratory distress syndrome. 

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The investigators concluded that, “Key features of the lung microbiome (bacterial burden, enrichment with gut-associated bacteria) predict outcomes in critically ill patients.” They added that, “The lung microbiome is an understudied source of clinical variation in critical illness, and represents a novel therapeutic target for the prevention and treatment of acute respiratory failure.”

Future prospective studies should investigate whether the microbiome’s role in lung disease is more attributable to remote (gut-lung) or local (lung-lung) host-microbiome interactions, as well as collecting time-matched specimens from the lower and upper gastrointestinal tract.

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Dickson RP, Schultz MJ, van der Poll T, et al; on behalf of the BASIC Consortium  Lung microbiota predict clinical outcomes in critically ill patients [published online January 24, 2020]. Am J Respir Crit Care Med. doi:10.1164/rccm.201907-1487OC