Confidential study of deaths following healthcare-associated infection (HCAI) and linkage of surveillance and mortality data

The joint project by the Health Protection Agency (HPA) and Office for National Statistics (ONS) to further understanding of mortality following MRSA infection, has reported on the progress made in establishing robust methods for both the linkage and investigation of deaths in its first year [1]. The two year project commenced in August 2005 with funding from the Department of Health [2].

The pilot phase of the data linkage study investigated whether infection records held by the HPA could be reliably linked to mortality records held by ONS. The lack of a well completed, unique identifier in infection records meant deterministic record linkage could not be applied and a probabilistic method was developed [3]. The method was developed and trialled using invasive Streptococcus pneumoniae infection records sampled from reports made between 1 July 2003 and 30 June 2004 linked to mortality records from 1 July 2003 to 31 March 2005. These same S. pneumoniae records were submitted to the NHS Central Register (NHSCR) Tracing Service for evaluation of the linkage mechanism by providing information on outcome from an independent source. Reports of invasive S. pneumoniae infections were used in this work because they contain full surname data (which MRSA data do not) which is required to enable matching by the NHSCR. Both methods were shown to be of similar accuracy with respect to identifying individuals who had died following infection.

Following the successful development of a probabilistic method for the linking of infection and mortality records, the method is now being used to link MRSA infection records to mortality records to enable analyses of mortality following invasive MRSA infection and certification of cause of death for these patients.

The pilot phase of the National Confidential Study of Deaths Following Healthcare-Associated Infection is a qualitative clinical review of patients who have died following an MRSA infection, to describe and evaluate the relative importance of key events leading up to death.

Cases for the pilot phase were identified retrospectively from a random sample of death registrations with any mention of MRSA on the death certificate. Nine hospitals were visited by the study investigator and 18 patients reviewed. The data collated comprised a review of medical records, interviews with infection control staff, and consultants responsible for the patients, as well as a questionnaire to gather organisational data on the management of infection control. All data were reviewed by an independent multidisciplinary panel of six clinical experts specifically convened for the study, with the aim of reaching a consensus on the relative contribution of different factors, in particular the MRSA infection, to the patient?s death [4].

The main phase of the Study will use the same methods to review a small sample of patients drawn from the linked data (ie patients with invasive MRSA infection who subsequently die in hospital). Unlike the pilot phase, sampling of cases is carried out independently of whether MRSA was documented on the death certificates.

For further information on the Data Linkage Study or Confidential Study of Deaths following HCAI please contact Nicola Potz ( or David Bridger (, respectively, at the Department of Healthcare Associated Infection and Antimicrobial Resistance, Health Protection Agency Centre for Infections, London.

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