hospital outbreak increased 3- to 4-fold. Subsequently, an outbreak of nosocomial infections (pulmonary and bacteremic) occurred in the surgical intensive care unit of the same hospital due to a strain of multiresistant Acinetobacter calcoaceticus (60). The organism was resistant to all antimicrobials ordinarily employed against Gram-negative aerobic bacilli: aminoglycosides (including amikacin); ampicillin; antipseudomonal penicillins; first-, second-, and third-generation cephalosporins; cephamycins; fluoroquinolones; aztreonam; imipenem; chloramphenicol; etc. The only antimicrobials to which the A. calcoaceticus isolates were susceptible were ampicillin–sulbactam (sulbactam responsible for the bactericidal effect of the combination) and polymyxin.
The above-described sequential outbreaks of nosocomial infections due to increasingly resistant organisms emphasizes the potentially great selective power of extensive antimicrobial use in a given institution, particularly in intensive care units, in favoring emergence of multiresistant pathogens.
In the past the rate of introduction of new antimicrobial drugs has been sufficient to counter those infections caused by organisms resistant to available drugs. Although there are >155 antibiotics (14), the rate of introduction of genuinely new drugs with different modes of action or genuinely different spectra of activity into clinical usage has slackened. Therapeutic options for nosocomial infections are increasingly limited because of antimicrobial resistance.
Control of this group of infections merits consideration of changes in some current practices. (i) Monitoring of nosocomial pathogens and their resistance patterns in acute-care hospitals. Although it is common practice for hospital microbiology laboratories to collect data on the antimicrobial susceptibilities of major pathogens and to provide summary information to physicians, such data commonly is tabulated for the recent year's experience, encompasses results from all parts of the hospital (including ambulatory services), and is provided to the physicians months later. This information is helpful for guidance in antimicrobial selection when a given pathogen has been identified or is suspected but its antimicrobial susceptibilities have not yet been determined. However, such information is less helpful in identifying early phases of nosocomial outbreaks in specialized units, since the data may become available late in the outbreak and may be obscured by collating susceptibilities from all parts of a hospital. In addition, data is not readily available in the form of antimicrobial-resistance patterns. Early detection of outbreaks of nosocomial