Study objective: To study sequences of colonization of different species of microorganisms and to determine the importance of gastric colonization for the development of nosocomial pneumonia.
Design: A prospective study.
Setting: Two identical ICUs of a university hospital.
Patients: Sixty-four patients admitted to ICU for at least 5 days; 59 were intubated.
Interventions: Microbiologic cultures of serially taken samples of gastric aspirates, oropharyngeal swabs, and tracheal aspirates were performed at the time of ICU admission and subsequently twice a week. Diagnosis of pneumonia was based on quantitative cultures from bronchoalveolar lavage (BAL) and protected specimen brush (PSB). Sequences of colonization were examined by comparing isolates of the same species, with concordance of minimum inhibitory concentration values to six antibiotics.
Measurements and results: Eleven patients developed 14 episodes of nosocomial pneumonia, yielding 20 species of microorganisms. Seventeen of 20 species (85 percent), associated with pneumonia, were cultured, previous to or on the day of diagnosis, from tracheal aspirates, and 6 of 20 (30 percent) species were cultured from gastric samples. A sequence of colonization from the stomach to the upper respiratory tract eventually leading to pneumonia was not observed in any of the six species. Initial colonization with Pseudomonas aeruginosa and Enterobacter species was more often demonstrated in the trachea (16/24 and 13/25 cases) as compared with the stomach (1/24 and 6/25 cases; p < 0.0001 and p = 0.02 respectively). In contrast, initial colonization with Klebsiella species and Enterococcus faecalis was more frequently demonstrated in the stomach (13/28 and 8/15 cases) as compared with the trachea (6/28 and 0/15 cases; p = 0.02 and p < 0.0001, respectively).
Conclusions: Based on studying sequences of colonization in ICU patients, we concluded that the stomach is unlikely to be an important source of pathogens leading to nosocomial pneumonia as diagnosed by BAL/PSB. Furthermore, the initial site and route of colonization might not be the same for all microorganisms.