Controlling an Outbreak of Pseudomonas aeruginosa in a Neonatal Intensive Care Unit: Multivariate Analysis of Risk Factors through a Case- Case- Control Study

Herruzo R, Ruiz G, Rubio M, Cruz-Troca JJ, Mora E and Perez J

Background: Neonates are very susceptible to Pseudomonas aeruginosa.

Aim: To describe a P. aeruginosa outbreak in our Neonatal Intensive Care Unit (NICU), and understand the underlying individual risk factors for colonization or infection, using a case-case-control design.

Methods: Microbiological studies were done routinely in our neonates to identify and instigate contact precautions if P. aeruginosa was present. If found, a search was made for possible environmental reservoirs and Random Amplification of Polymorphic DNA (RAPD) was run on all isolated P. aeruginosa. We divided our children into two cohorts, (with and without this microorganism). Finally we designed a case-case-control study to evaluate predictive factors in those infants colonized or infected by P. aeruginosa.

Results: In 4 months, 14 infants were infected and 16 were only colonized by P. aeruginosa. All the P aeruginosa isolated from these children were identical on RAPD, but this organism was not found in any environment reservoirs. Separation by status into two cohorts helped to reduce new cases, but global number of cases (sum of the new and existing cases each week) took longer to fall. In the same time period another 82 NICU-patients had not P. aeruginosa, and they were used as controls. Bivariate and multivariate analysis determined the factors associated with colonization or infection by P. aeruginosa.

Conclusion: Risk factors of infected neonates: fungal infection, number of cases in previous week and separation into cohorts (protection factor). In colonized, birth malformations were added to above risk or protection factors.