Emergence of resistant bacterial strains during treatment of infections in the respiratory tract.

In order to investigate the frequency of the emergence of resistance during treatment, 1,403 episodes of lower respiratory infection were studied in a General Hospital with three departments of Chest Medicine in a period of four years. In 650 episodes the pathogen was isolated and in 82 of those failure of therapy was accompanied by emergence of resistance to the agent used. Factors associated with this phenomenon were: intensive care, tracheostomy, involvement of Pseudomonas aeruginosa, Enterobacter spp., Serratia marcescens, Staphylococcus aureus or Acinetobacter calcoaceticus, use of antipseudomonas penicillins, cefotaxime (especially when used in P. aeruginosa infections) and co-trimoxazole and monotherapy as opposed to appropriate combination therapy in patients with nosocomial pneumonia.