To minimise HCAI in haemodialysis patients with a CVC, it is essential that infection prevention and control within the haemodialysis environment takes an evidence-based approach to ensure optimal management of CVCs. This includes accurate diagnosis and monitoring of bloodstream infections using standardised case definitions and, adopting components of an infection prevention and control programme and quality improvement initiatives (chapter 2, section 2.5) that are aimed at ensuring safe and effective healthcare (Health Information and Quality Authority 2009).
Bloodstream infections can be classified according to surveillance or clinical case definitions. Surveillance definitions include the European Centre for Disease Prevention (ECDC 2012), the CDC/NHSN central line-associated bloodstream infection (CABSI), also known as laboratory-confirmed bloodstream infection (CDC/NHSN 2009) and the CDC/NHSN Dialysis Event Module Bloodstream Infections (CDC/NHSN 2009). Prior to the establishment of the ECDC, the Hospital in Europe Link for Infection Control through Surveillance (HELICS) developed case definitions relevant to CVC-related infections.
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The HELICS (2004) protocol includes case definitions for bloodstream infection and CVC-related infection, developed for the surveillance of nosocomial infections in Intensive Care Units (ICU). The case definition relating to bloodstream infection is not concerned with the source of the infection, but the case definition for CVC-related infection addresses three issues. The first two relate to local and general CVC-related infection, both of which do not require positive blood cultures, lack clarity on what constitutes a CVC culture and are very broad definitions. The third is linked to CVC-related bloodstream infection. The HELICS definitions, while suitable for surveillance of bloodstream infection rates specific to ICU patients, may not be suitable for clinical diagnosis or research-based activities, especially in the field of outpatient haemodialysis care, as it may result in decreased specificity1 (Kallen 2013).
The CDC/NHSN surveillance case definition for CABSI differs from HELICS in that it was developed for different inpatient areas, including inpatient dialysis units (CDC/NHSN 2009). Laboratory-confirmed bloodstream infections criteria are used to classify primary bloodstream infections, which are classified as CABSI infections, if the central line was in place 48 hours before the onset of the infection. Greater detail on this case definition is provided in chapter 8 (section 8.14.1). The advantage of this definition is that it removes any clinical uncertainties relating to secondary bloodstream infections and common skin contaminants. Culturing of the catheter tip is not a criterion for CABSI. A case definition on clinical sepsis is also provided, but this only applies to neonates and infants under the age of one. A potential weakness of this definition is that it may over-estimate the true rate of CVC-related infections due to difficulty in differentiating central line infections from remote unrecognised infections. Other limitations include inter-observer variability and a lack of standardisation in the surveillance process (The Joint Commission 2012).
The CDC/NHSN2 (CDC/NHSN 2009) was the first organisation to develop a
surveillance protocol that includes dialysis events related to vascular access use, including CVC use. These events are specific to patients attending outpatient haemodialysis settings and include hospitalisation, the start of an intravenous (IV) antimicrobial and positive blood cultures. As outlined in chapter 8 (section 8.14.3), the dialysis event surveillance protocol also
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Specificity is the ability to identify correctly those who do not have the condition. 2 CDC/NHSN updates the dialysis event protocol on a regular bases, the trial protocol is informed by the CDC/NHSN protocol published in 2009.
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includes three infection-related case definition outcomes: local access infection; access-associated bacteraemia and vascular access infection. Although simple and easy to use, these case definitions lack the specificity necessary for clinical diagnosis and may not be sufficiently robust for research studies. However, an advantage of the dialysis events protocol is the reporting of dialysis events per 100 patient-months and the collection of denominator data (number of CVCs) on the first two working days of each month. This is less labour-intensive than collecting denominator data for line days (reported as 1000 catheter line days) that requires counting the number of patients with one or more CVCs at the same time each day during a specific month. This is not suited to an outpatient haemodialysis setting as patients visit the unit every second day. The use of the dialysis events surveillance protocol is widespread in outpatient haemodialysis units in the US, with a number of European and non-European dialysis units also reporting its use (Tokars et al. 2002, Klevens et al. 2005, George et al. 2006, Klevens et al.
2008, El-Saed et al. 2011, Bajwa et al. 2012).
The Infectious Diseases Society of America (IDSA) (Mermel et al. 2009), in their 2009 update on clinical practice guidelines for the diagnosis and management of intravascular catheter-related infection, recommended a specific clinical case definition for catheter-related bloodstream infections (CRBSI); chapter 8 (section 8.14.1) provides greater detail on this particular case definition. Clinical findings alone, due to their poor sensitivity1 and specificity2, are not sufficient or reliable for diagnosing CRBSI (Mermel et al.
2009, SARI 2009). A diagnosis of CRBSI is dependent on a number of measures including culturing the tip of the CVC and blood cultures. The semi- quantitative catheter segment culture is a method that cultures the outside of the catheter segment, while the quantitative segment catheter culture is concerned with the intra-luminal spread of organism. The quantitative culture method is labour-intensive and time consuming. It has been reported that the semi-quantitative method has high sensitivity, especially in recently inserted catheters. For long-term catheters, the semi-quantitative culture method may be less sensitive to intra-luminal spread of organisms, when compared to the quantitative catheter culture method. However, there is much debate within the literature as to which method is the more sensitive (Bouza et al. 2005, Safdar et al. 2005, Mermel et al. 2009, SARI 2009). Indeed, both approaches
1 Sensitivity is the ability to identify correctly those who have the condition. 2Specificity is the ability to identify correctly those who do not have the condition.
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are recommended by the European Renal Dialysis Association best practice guidelines (Vanholder et al. 2010).
CRBSI can be diagnosed without removal of the CVC, using blood culture diagnostic methods including simultaneous quantitative cultures of blood and differential time-to-positivity cultures. The simultaneous quantitative cultures of blood are labour-intensive and expensive. Differential time-to-positivity cultures are dependent on drawing positive simultaneous blood cultures from the CVC and peripheral vein (Blot et al. 1998, Raad et al. 2004, Allon 2009). However, it is not always feasible to draw peripheral blood cultures from haemodialysis patients. First of all, peripheral cultures cannot be obtained from vessels intended for future AVF formation. Secondly, patients’ vasculature may be so poor that a peripheral sample cannot be obtained. In these circumstances, a peripheral sample may be obtained, during dialysis, from the dialysis circuit lines. However, there is a lack of clarity as to whether there is any difference between cultures drawn directly from the catheter and from the dialysis circuit lines (Mermel et al. 2009, Vanholder et al. 2010).
The strength of the CRBSI case definition lies in its precision and the inclusion of specific requirements detailing what constitutes a CVC culture. As outlined above, these include specific laboratory testing and, as a result, diagnosis is less open to interpretation, making CRBSI case definitions more suited for clinical research activity (Association for Professionals in Infection Control and Epidemiology 2009). The precision of this case definition can also be a weakness as a number of specialised blood culture tests are required to confirm CRBSI diagnosis, tests that may not routinely be undertaken in hospital laboratories aligned to outpatient haemodialysis units or tests requiring specific blood culture samples that may not be attainable from haemodialysis patients. In addition, there is a reluctance to remove the CVC, as it is the patient’s only form of vascular access for haemodialysis, making it impossible to culture the tip of the catheter (The Joint Commission 2012, Kallen 2013).
Finally, SARI (2009) in its published guidelines on the prevention of intravascular catheter-related infections in Ireland recommends the use of CABSI and CRBSI case definitions in the diagnosis and monitoring of bloodstream infections. Specific reference is also made to the outpatient
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haemodialysis setting and the use of the CDC/NHSN dialysis events outcomes in the surveillance of infection within this patient population.