Pseudomonas aeruginosa (Pa) is a frequent nosocomial pathogen in the ICU setting, often associated with water and ventilator circuits. Patient to patient spread is suspected but not well documented.

Five of 5 patients in a small surgical NICU either were colonized or infected with Pa. Infections included line associated abscess, tracheobronchitis, wound infection (2), including postoperative myelomeningocele wound breakdown. One patient colonized with Pa was readmitted with VP shunt infection. To investigate this outbreak, a better understanding of the epidemiology of the organism was needed. Adequate typing of the organism was essentail in this process. Molecular epidemiologic techniques were used to type the isolates. 4/5 patient's isolates were typed by antibiotic susceptibility patterns, and biotyping. In addition, we subjected these isolates to pulsed field gel electrophoresis (PFGE), which specifically identified the strains by their DNA patterns. All isolates had the same DNA banding and were identical. The index case was transferred from another NICU with documented pseudomonal endotracheal tube colonization 6 weeks prior, and the earlier isolate from this patient's trachea was also identical to the later isolates. No further patients were admitted to the NICU, and the outbreak was eradicated. This organism was uncommon in this unit before the outbreak and remains uncommon after the outbreak.

Molecular epidemiologic methodology, specifically, PFGE was valuable as a means of determining the source of an outbreak of invasive Pa with clear patient to patient spread. It also has provided some insight into how microbial strains become established in specific hospital areas. It is clear that patients transferred into units can alter the existing microbial patterns and prior patient isolates should be taken into consideration in the management of these patients.