"This is a landmark study not only because of its size, but also because we followed what happened to patients. This meant we have been able to show confidently which are the best tests to use to diagnose C-diff," says Mark Wilcox. (Credit: Chris Watkins/Flickr)

For bacterial infection, which test is best?

Researchers have identified the most effective test for diagnosing a bacterial infection that causes about 20,000 deaths a year in US hospitals.

Clostridium difficile (C-Diff) affects the digestive system, and is most common in hospital patients treated with antibiotics for other infections.

Scientists tested more than 12,000 fecal samples from hospital patients to establish the best method for diagnosing C-Diff. The findings appear online in the journal Lancet Infectious Diseases.

“The diagnosis of C-Diff has become a complicated area with lots of alternative tests, and there has been considerable uncertainty about which are the best tests to use,” says Mark Wilcox, a professor at the University of Leeds and Leeds Teaching Hospitals NHS Trust, who is also the C-Diff lead for Public Health England, the nation’s public health body.

“This is a landmark study not only because of its size, but also because we followed what happened to patients. This meant we have been able to show confidently which are the best tests to use to diagnose C-diff.”

The study compared the main different ways of diagnosing C-Diff, including the two “gold-standard” methods: a cytotoxin assay, which looks for the presence of C-Diff toxin in fecal samples; and cytotoxigenic culture, which looks to see if there are bugs present in fecal samples that could possibly produce C-Diff toxin.

The research team found that patients with fecal samples positive by the cytotoxin assay were almost twice as likely to die within 30 days as those patients with samples only positive by the alternative ‘gold-standard’ method (16.6 percent versus 9.7 percent).

Tests that detect the presence of toxin in fecal samples (the cytotoxin assay) are the most reliable indicators of true C-Diff, according to the study results. The research has already been used as a basis for new 2012 guidelines to the National Health Service (NHS) on the diagnosis of the infection.

C-diff cases in the NHS have decreased markedly in number since their peak in 2007-08 but reliably diagnosing C-diff is a crucial way forward to continuing to fight this infection,” says Wilcox.

These findings highlight the importance of using appropriate tests to diagnose C-Diff, especially as it is not possible to diagnose the infection using laboratory tests. Treating patients for C-diff and preventing the spread of infections in hospitals rely on accurately identifying who has the infection, as well as those who may be capable of transmitting the bug.

The UK Department of Health and the Health Protection Agency, now known as Public Health England, funded the research, which was carried out by researchers at the University of Leeds, in partnership with colleagues from the University of Oxford, University College London, and St George’s, University of London.

Source: University of Leeds

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