Transmission of nosocomial pathogens

Prevention of the spread of antibiotic-resistant micro-organisms is one of the challenges for mankind in the new millennium, according to a recent report from the World Health Organization. In our Western world resistance problems occur mainly in intensive care units (ICUs). However, the observed numbers of infections are only the tip of the iceberg of patients colonised with multiple-resistant pathogens. Remarkably, manifestation of problems with antibiotic resistant pathogens within ICUs has specific characteristics. Initially there are a few, presumably sporadic, infections, and sometimes an outbreak is feared. Such an initial outbreak may be caused by an environmental source within the ward or by the admission of a patient colonised or infected with the resistant pathogen. After some time, the incidence of infections increases and a considerable part of the patient population appears to be colonised. A situation of endemicity has developed and the eradication of the resistant micro-organisms from the ward is very difficult and may even be impossible. Classical measures of infection prevention such as hand disinfection after patient contact remain the cornerstone of infection prevention, but little is known about their quantitative effects. Compliance with this rule is not 100%, usually not even 50%, but what percentage would be sufficient, and can other measures be more effective? Modelling the dynamic processes that determine the epidemiology of colonisation may help to quantitatively predict what effects will influence this process. Moreover, these methods may help to identify new measures for infection control.