Community Clostridium difficileBMJ 2009; 338 doi: https://doi.org/10.1136/bmj.b2195 (Published 03 June 2009) Cite this as: BMJ 2009;338:b2195
All rapid responses
Rangaiah and colleagues examined their laboratory results for
Clostridium difficile toxin tests to understand GP requesting for the
investigation of C difficile infection (CDI). They comment that
‘currently used tests are not very sensitive’. This is true
(sensitivities vary between 80% and 90% for most commercial immunoassays),
but of at least equal concern is the likelihood of false positive results
with the commonly used commercial toxin detection kits.[2,3] The
specificity of there commercial assays ranges from 97% to 99%, meaning
that approximately 1-2 out of every 10 positive results using these kits
are in fact incorrect.[2,3] False positive results are even more likely
when testing faecal samples from the community, where the prevalence of
CDI is expected to be much lower than in hospitals. Alerts have
recently been issued about the poor accuracy of these methods with the
advice that laboratories do not rely on single tests for the detection of
C difficile toxin.
The authors quote a study by one of us (MHW) to emphasise the
importance of recent hospital admission and antibiotic treatment as major
risk factors for community associated CDI. They do not point out that
this study (and others) show that about a third of community-associated
CDI cases have neither of these risk factors. Thus, GPs should not
rely on such factors alone to arouse suspicion of community-associated
CDI. We point out that the Department of Health and Health Protection
Agency 2009 guidelines state that ‘All cases of diarrhoea among people in
the community aged 2 years and above should be investigated for CDI unless
there are good clinical or epidemiological reasons not to’. We are
concerned that all laboratories should be using the same testing criteria
for C. difficile, so that CDI cases are not missed and the value of
mandatory surveillance data is not reduced. Unfortunately, sub-optimal C.
difficile tests also undermine surveillance and potentially control
measures for CDI. The optimum use of available tests for C. difficile
infection, including combinations of assays, needs to be defined.
1. Rangaiah J, Wilks M, Millar M. Community Clostridium difficile.
2. NHS Purchasing and Supplies Agency, Centre for Evidence based
Purchasing. Clostridium difficile toxin detection assays. Evaluation
report CEP08054, 2009. Wilcox MH, Eastwood KA. Available at:
Accessed 4th June 2009.
3. Planche T, Aghaizu A, Holliman R, Riley P, Poloniecki J,
Breathnach A, Krishna S. Diagnosis of Clostridium difficile infection by
toxin detection kits: a systematic review. Lancet Infect Dis 2008;8:777-
4. Wilcox MH, Mooney L, Bendall R, Settle CD, Fawley WN. A case-
control study of community-associated Clostridium difficile infection. J
Antimicrob Chemother 2008;62:388-96.
5. Health Protection Agency C. difficile Diagnosis Working
Group:Questions and answers about the laboratory diagnosis of Clostridium
difficile infection, www.hpa.org.uk/infections/cdifficileq&a.
6. Clostridium difficile infection: How to deal with the problem.
Department of Health and Health Protection Agency, 2009. Available at:
http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1232006607827. Accessed 4th
Competing interests: No competing interests