MICROBIOLOGICAL SURVEILLANCE DURING SELECTIVE DECONTAMINATION OF THE DIGESTIVE-TRACT (SDD)

The use of selective decontamination of the digestive tract (SDD) as p rophylaxis against nosocomial respiratory tract infection remains cont roversial, largely because of concerns that, in the long term, it may promote the emergence of antibiotic-resistant strains. This report des cribes the results of surveillance cultures and susceptibility testing undertaken during the course of a 2-year, double-blind study of the e fficacy of SDD which was conducted in a respiratory intensive care uni t (ICU). Surveillance specimens from the alimentary tract and trachea were obtained from each patient on admission and then twice weekly unt il 48 h after discharge from the unit. Specimens were cultured semiqua ntitatively and organisms from morphologically distinct colonies were identified by standard methods; the susceptibilities of these isolates were determined by the disc diffusion method. Five thousand, nine hun dred and sixty surveillance samples from 239 patients were processed i n this way. Compared with the placebo group, SDD caused a significant reduction in the incidence of colonization of the alimentary tract wit h aerobic Gram-negative bacilli (AGNB), and Candida spp. were almost t otally eliminated. The incidence of colonization with enterococci incr eased in both groups, while the incidence of both colonization of the alimentary tract with strains of coagulase-negative staphylococci and methicillin-resistant Staphylococcus aureus and infection caused by th ese organisms increased in the SDD group. Acinetobacter spp. were the most common bacteria associated with unit-acquired colonization and lo wer respiratory tract infection in both groups. The acquisition of str ains of Pseudomonas aeruginosa and cefotaxime- and/or tobramycin-resis tant Enterobacteriaceae was significantly greater in the placebo group than in the SDD group, although tobramycin-resistant strains of Prote us, Morganella and Providencia spp. were isolated from three of 114 pa tients receiving SDD. The use of SDD did not lead to an overall increa se in antibiotic resistance amongst the AGNB usually associated with I CU-acquired infection. However, colonization with strains which were e ither resistant to one or more of the antibiotic components of the reg imen or which were not inhibited by the regimen was observed and may s ubsequently lead to infection.