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Clostridium difficile Deaths - The Coverage of the Statistics

19 September 2008

The General Register Office for Scotland (GROS) applies the rules of the International Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10), in order to determine the ICD-10 code for each death registered in Scotland.  The complexity of these rules can result, in some cases, in the cause of death coded by GROS differing from that which a health board would choose.  For example, the ICD-10 rules state that, if certain specific conditions are mentioned in Part I on the death certificate, they should be considered as obvious consequences of certain other conditions.  This means that if Part I(a) contains “Septicaemia” and Part I(b) contains “Clostridium difficile”, a code which is associated with Clostridium difficile will be chosen as the underlying cause of death.

The guidelines for coding set out by the World Health Organisation, and applied by GROS staff with advice from the Information Services Division of NHS Scotland, in relation to Clostridium difficile are:

• code A04.7 - "Enterocolitis due to Clostridium difficile" - applies when the death certificate mentions "Clostridium difficile" along with “Enterocolitis” or “Diarrhoea”;

• code A41.4 - "Septicaemia due to anaerobes" - applies where the death certificate mentions “Septicaemia  or  septicaemia due to anaerobes”  along with any wording associated with “Clostridium difficile”;

• code A49.8 - ”Other bacterial infections of unspecified site” - applies when “infection” is included on the death certificate together with “Clostridium difficile”, or when “Clostridium difficile” is mentioned on its own.

• code A09 - "Diarrhoea and gastroenteritis of presumed infectious origin" - applies when there is a presumed infectious origin of diarrhoea and gastroenteritis along with any wording associated with “Clostridium difficile” on the death certificate.

(Of course, the figures for Clostridium difficile deaths do not include cases where codes A41.4, A49.8 and A09 were used without any mention of Clostridium difficile.)

For the purposes of producing the statistics shown in the accompanying tables, GROS creates an "extract" file which contains copies of the records for all deaths which might potentially involve Clostridium difficile.  These are identified as follows:

• all deaths which have the code A04.7 "Enterocolitis due to Clostridium difficile" are included automatically;
• deaths which have the code A09 "Diarrhoea and gastroenteritis of presumed infectious origin", A41.4 "Septicaemia due to anaerobes" or A49.8 ”Other bacterial infections of unspecified site” are clearly candidates for inclusion.  However, deaths for which other codes have been assigned may have Clostridium difficile mentioned.  Therefore, GROS searches the cause of death text from all deaths for a mention of:

            o    Clostridium difficile;
            o    something that is clearly an abbreviation (e.g. "C. diff."); 
            o    Clostridium (but no mention of "difficile") and also a 
                  mention of "colitis", "bowel infection", "diarrhoea" or similar; or 
            o    pseudomembranous colitis (a condition which is almost always caused by 
                  Clostridium difficile);

All cases which contain such text are included in the "extract" file.  However, deaths where the text simply states "Clostridium infection" are excluded.  Detailed inspection of the text is required because of numerous spelling errors and non-standard abbreviations. These selection criteria were agreed with GROS's medical adviser.

For each death, GROS assigns a single code for the underlying cause of death and, depending upon what was written on the death certificate, may assign several other codes for other factors which contributed to the occurrence of the death. Statistics on three bases can therefore be produced from the records in the "extract" file:

• deaths for which Clostridium difficile was the underlying cause - the only records counted are those which have an "underlying cause" code of A04.7, A09, A41.4 or A49.8 and a mention of "Clostridium difficile" [Footnote 1];     
• deaths for which Clostridium difficile was a contributory factor - the records counted are those which have a mention of "Clostridium difficile" [Footnote 1] but the "underlying cause" code is not A04.7, A09, A41.4 or A49.8;
• deaths for which there was any mention of clostridium difficile - all records which have a mention of "Clostridium difficile" [Footnote 1] are counted.  

1. or something equivalent - a condition which must be satisfied for the records to be included in the "extract" file