M Wolkewitz¹, M Dettenkofer², H Bertz³, M Schumacher¹ and J Huebner⁴

¹Institute of Medical Biometry and Medical Informatics, University Medical Center Freiburg, Germany. ²Institute of Environmental Medicine and Hospital Epidemiology, University Medical Center Freiburg, Germany. ³Department of Internal Medicine I (Haematology/Oncology), University Medical Center Freiburg, Germany. ⁴Division of Infectious Diseases, University Medical Center Freiburg, Germany.

Abstract

Background: In addition to the close contact between patients and medical staff, the contamination of surfaces plays an important role in the transmission of pathogens such as vancomycin-resistant enterococci (VRE). Mathematical modeling is a very convenient tool for hospital infection control as it allows the quantitative prediction of the effects of special hygiene and control interventions.

Methods: We present a compartmental model which describes the dynamics of transmission from patient to patient, also taking into account the interaction with medical staff and environmental contamination. Empirical data from a VRE outbreak in the onco-haematological unit at the University Medical Center Freiburg (Germany) were collected with 100 consecutive admissions being followed up for 90 days. Stochastical simulations were used to predict the prevalence of patients colonised with VRE at the time when at least one of the following interventions were introduced: hand hygiene, disinfection of sur- faces, cohorting, screening and antibiotic reduction.

Results: Graphical figures show the temporal dynamics of several simulation scenarios. If no prevention or intervention is present, simulations based on transmission models predict an expected endemic prevalence per ward of 0.83 (95% CI:0.66, 1.00) after the first infected person enters the unit. Interventions may reduce this prevalence, but only the combination of several interventions can control a VRE outbreak.

Conclusions: The model predicts that only the combination of several interventions can control an VRE outbreak in this setting. The inclusion of environmental contamination improves the compartmental model and allows a prediction of the efficacy of the disinfection of surfaces. These results can be applied to other settings and will therefore help to understand and control the spread of nosocomial pathogens.