Patients at risk of carrying hospital superbug C diff must be tested twice to ensure they are not misdiagnosed and to prevent spreading the bacteria, researchers at St George’s Hospital are warning.

The findings show that no single test is sufficiently accurate with as many as 20 per cent of real C diff cases being missed. And out of the 55,000 cases reported in England each year, around 20 per cent - up to 11,000 patients - being misdiagnosed.

Researchers warn that the misdiagnosis of C diff can have very serious consequences.

Lead author of the study, Dr Timothy Planche, Consultant in Medical Microbiology, St George’s Healthcare NHS Trust, said: “A false negative result could mean that infected patients don’t get the right treatment and could pass the infection on to others.

“Conversely, patients receiving a false positive result may receive inappropriate treatment and be placed in wards along with infected patients, putting them at risk of contracting the infection.”

Clostridium difficile is a hospital-acquired infection, which can lead to diarrhoea, severe inflammation of the bowel and can be fatal.

Patients most at risk are those on antibiotics and the elderly - over 80 per cent of those infected are over 65.

A quick and accurate diagnosis is vital to stop the bacteria spreading, alongside hand washing and regular cleaning of wards, bedpans and toilets.

Currently, patients across the NHS suspected of carrying the C diff bug only have one test, vhich measures toxin levels in stool samples.

However, following a review of 18 studies looking at the effectiveness of the six most common hospital tests, researchers say two separate tests must be used to avoid getting false positives and missing real cases.

St George’s Hospital has been piloting and monitoring a two-stage testing scheme over the past six months.

The researchers recommend a two-stage testing process, involving two different tests.

The first would be a quick test to weed out the negatives.

Stool samples returning a positive result on the first test would then be given a second test in order to weed out the false positives. St George’s Hospital and St George’s, University of London are at the forefront of implementing this two-stage approach and are currently analysing its impact.

The results of the research are on The Lancet Infectious Diseases website and will feature in the December issue of the journal.