confounding causes for HAI. Direct and conditional causes involve surgery, whereby wounds can become infected, resulting in SSI. Venous catheters, especially central venous catheters (CVC), form a port d’entrée too, allowing bacteria and other pathogens to enter the body and/or adhere to the vascular device and possibly develop into a bloodstream infection (BSI). Approximately half of BSIs are secondary to other infections, either community‐acquired or hospital‐acquired. Impaired mobility is a risk factor for developing hospital‐acquired pneumonia, and the risk is accentuated when invasive ventilation is required. Infections such as (ventilator‐associated) pneumonia and bacteraemia typically develop in seriously ill patients in whom such endogenous and exogenous factors coincide. Healthcare‐associated infections in these patients may be more challenging to prevent. Urinary catheters increase the risk of UTI, which, although less serious than SSI, BSI or pneumonia, is a frequent nosocomial infection and can result in secondary bloodstream infection. Antibiotic use can cause a severe imbalance in the human microbiome, increasing the risk of infections with opportunistic pathogens that thrive under selective pressure. The risk of acquiring a nosocomial infection is further enhanced by the frequent contact with HCWs and with other patients (through HCWs, fomites or the environment). Moreover, nosocomially transmitted pathogens are sometimes antibiotic‐resistant organisms that thrive in hospitals where antibiotics are more frequently prescribed than in the community. An infection with a resistant micro‐ organism may result in a delay of adequate treatment[12]. Almost all HAI cause delayed or inadequate recovery, additional pain and/or anxiety, and sometimes result in secondary bloodstream infection, sepsis and even permanent disability or death [10, 13‐ 20]. Cassini et al. estimated that in 2011‐2012, the burden of the five major HAI (SSI, BSI, pneumonia, UTI and CDI) together with healthcare‐associated neonatal sepsis in the European Union was 501 (95% CI 429‐582) disability‐adjusted life‐years (DALYs) per 100,000 inhabitants of the general population [10]; the burden of antibiotic‐resistant infections, mostly hospital‐acquired, was 131 (113‐149) infections per 100,000, with an attributable mortality of 6.4 (5.5‐7.5) per 100,000 (2015 data). The burden is lowest (<50/100,000) in the Netherlands, Scandinavian countries and a few others [15]. Although the recent focus has been very much on antibiotic resistance, these figures show that HAI with non‐resistant micro‐organisms likewise result in morbidity and mortality. HAI can be expressed as an incidence (e.g. events per 100 or 1,000 patients or hospital admissions) or an incidence density (e.g. events per 1,000 patient‐days or device‐days) when exposure time is taken into account. Incidence‐based surveillance is 1 11 Introduction
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