Tracheal colonization has been associated with subsequent development of ventilator-associated pneumonia. Little is know about the density of and change in colonization over time.We did a prospective study to examine the pattern and density of tracheal colonization during the initial days of mechanical ventilation in the intensive care unit (ICU).
Subjects were enrolled if they were intubated for less than 24 hours and were predicted to stay intubated for 4 days and had a legally authorized representative that signed consent. Tracheal aspirates were collected everyday for the first 4 days of intubation via sterile in-line suction catheter on to a sputum trap using 2ml of saline. Specimen was transported immediately to microbiology laboratory and quantitative cultures obtained. Density of colonization is reported as microbial index which is the sum of log colony forming units of all growth.
29 subjects (16 men) have been recuited thus far. Mean age is 56 years. Mean ICU and hospital stay is 9 and 20 days respectively. 19/29 were receiving antibiotics on the first day of intubation. Proportion colonized was 63%, 72%, 76% and 93% on Days 1, 2, 3 and 4 respectively. Mean microbial index increased progressively (2.9 on day 1 and 4.2 on day 4). When subjects were colonized from day 1 (n=19), the colonization was persistent for all 4 days. Among those who were sterile on day 1 (n=11), 3 subjects remained sterile and 2 subjects had transient colonization. Among the early colonizers, there was very little acquisition of new bacteria.
About two thirds of subjects are already colonized within 24 hours of intubation. Density of colonization increases with the duration of intubation. Initial colonizers are relatively resistant to acquisition of new bacteria.
Future studies should explore for differences in susceptibility to nosocomial pneumonia between early and late colonizers.
Lakshmi Durairaj, None.