Trusts that have failed to meet their C difficile infection targets because of changes in how patient tests are carried out are challenging the “achievability” of even tougher measures.

Around half of trusts have now adopted two-stage testing for C difficile, in line with guidance issued by the Department of Health and Health Protection Agency in March 2009.

This involves an initial test to weed out negative cases, followed by a second test to confirm the positives. It is expected to become mandatory after a DH review publishes its conclusions in the summer.

HSJ has learned that a number of trusts that used the new testing technique in 2010-11 failed their target for that year and are challenging the 2011-12 objective, which requires a 29 per cent reduction on 2009-10 levels.

They include Guy’s and St Thomas’ Foundation Trust in London, which at the end of February had exceeded its target of 91 cases by 19, and Taunton and Somerset Foundation Trust, which had 64 cases against an annual threshold of 60.

Both trusts blamed the breach on the more sensitive test. A report to Taunton and Somerset’s board revealed the trust had “challenged the achievability” of its target of 44 cases during 2011-12 as a result.

DH guidance encourages commissioners to impose financial sanctions where breaches of the target cannot be clinically justified.

However, commissioners for both trusts have agreed not to impose sanctions for failures during 2010-11 in recognition of the impact of the new testing.

A spokesman for NHS Somerset said the primary care trust recognised that “the two-stage test regime for C difficile may present a challenge” but there is a “shared understanding and expectation that there will continue to be a downward trend in cases”.

The new objective is the first nationally set C difficile target since 2007-08, when trusts were challenged to reduce infections by 30 per cent in three years. This was achieved within a year and targets were set locally in 2009-10 and 2010-11.

A DH spokeswoman confirmed a “very small number of trusts” have queried their expected objectives.

She said: “We will be challenging these trusts on their objectives during the current annual planning round.

“Although the objective is ambitious, it is also realistic, and no trust is required to deliver reductions that another organisation has not already achieved.”

C difficile performance figures for 2010-11 will be published by the HPA in the summer.