National guidelines for MRSA prevention were published in Germany in 1999  and each hospital must record the occurrence of MDRO such as MRSA since 2001, but without mandatory reporting . German microbiology laboratories have been participating in the European Antimicrobial Resistance Surveillance System (EARSS) and have provided the MRSA percentage of S.aureus bacteremia isolates for many years. Since 2008 a more comprehensive surveillance system for MDRO from laboratory data has been established (ARS = Antibiotika Resistenz-Surveillance, https://ars.rki.de). In 2009 a mandatory reporting of MRSA bacteremia cases was introduced . MRSA-KISS and the MDRO component of ICU-KISS were established in 2003 as voluntary surveillance systems. In 2009 about 10% of all hospitals were participating and about 15% of all ICUs.
Compared to the data from other countries the incidence density of nosocomial MRSA in German hospitals and ICUs is lower (especially considering that most publications report only nosocomial MRSA infections, not nosocomial MRSA cases (i.e. including colonized as well as infected patients) [7–9]. But of course there are also countries with lower MRSA rates. One example is the report from 38 French hospitals describing a decrease of the MRSA incidence density from 1.16 to 0.57 per 1000 hospital days between 1993 and 2007 .
Intensive care units participating in the MDRO component of ICU-KISS were able to achieve a significant decrease of ICU-acquired MRSA cases of 29% during a four-year surveillance period. This is in accordance with similar observations concerning the influence of surveillance activities on the development of nosocomial pneumonia and primary bloodstream infections in ICU-KISS. Significant reductions of infection rates of between 14 and 29% were demonstrated during various periods of analysis [11–14]. On the unit level, the surveillance staff together with the ICU staff can analyze the data at any time, present the information to the ICU staff and stimulate discussions to analyze reasons for infection control problems and to introduce the most appropriate interventions. Already in the second year of surveillance a significant effect was observed with further improvement in the following years.
However, no decrease in hospital-acquired MRSA rates on the hospital level was found. Normally, MRSA rates on the hospital level are presented during meetings of the hospital infection control committees. But, even if the hospitals have hospital-acquired MRSA rates above the median, the hospital committees are often not able to identify reasons for this situation and draw the most appropriate conclusions. A similar development was demonstrated within the other hospital-based surveillance system in KISS, the surveillance system for Clostridium difficile associated diseases (CDAD-KISS), where we also did not find a reduction of nosocomial cases within the first 3 years of participation. Perhaps the infection control staff has focused its activities on the ICU within their hospitals because they know that the highest MRSA rates can be observed on the ICUs and they are used to work in the field of quality management with the ICUs due to the experience from ICU KISS.
Moreover, many hospitals increased their admission screening frequency remarkably during the observation period. Without admission screening, cases with an MRSA positive microbiology report from day 3 on will be automatically considered hospital-acquired or ICU-acquired according to the MRSA-KISS and ICU-MDRO protocols. With admission screening, on the other hand, many cases will be classified as imported which would not be the case without admission screening. Due to this reclassification the constant hospital-acquired MRSA incidence in MRSA-KISS hospitals with continuous participation will be in reality associated with an increase of hospitals-acquired cases. For the ICUs we do not have the data about the development of admission screening. But we also expect an increase over the years along with the increase in the entire hospitals. Therefore the observed 29% decrease of the ICU-acquired MRSA incidence density has also to be regarded-at least in part-in the light of this re-classification bias.
Unfortunately we do not have comparable data from hospitals without continuous MRSA surveillance in Germany. The only data source available is the above mentioned ARS database, where the percentage of MRSA among S.aureus strains is provided for a large number of hospitals over time. According to this database a further increase of the percentage of MRSA was observed between 2008 and 2010 https://ars.rki.de.
Our data lead to the conclusion that a unit based surveillance approach (at least in the ICUs) is more useful for reducing nosocomial (i.e.acquired) MRSA rates compared to a hospital based approach. From the hospital level, the infection control staff has to identify the most problematic units and to provide a feedback on the unit level in order to stimulate appropriate interventions on the unit level.