The announcement of a public inquiry into the outbreak of clostridium difficile (C Diff) at Vale of Leven Hospital in Dunbartonshire was greeted with relief by the families of patients who had died. They had two reasons for rejoicing: at last they would discover the truth about what led to the deaths of their relatives and it would provide lessons for other hospitals.

"A public inquiry will mean that no other families will have to go through the agonies we have all suffered," said Michelle Stewart, secretary of the C Diff Justice Group, formed following the deaths of 18 people who contracted the illness at Vale of Leven Hospital last year. Nine of those deaths were directly attributable to C Diff and it was a contributory factor in the other nine. However, we now know that there were also 18 deaths directly attributable to C Diff at Gartnavel Hospital in Glasgow last year and a further 10 in 2007. Although the Gartnavel deaths occurred over a longer period and in a much bigger hospital, the fact that there were so many suggests there was also a particular problem there.

With a number of families now reporting where C Diff was not the main cause of death but a significant contributory factor, there is the separate issue of how the infection is recorded on death certificates. They should, of course, record the cause of death as accurately as possible.

Provisional figures for rates of C Diff across Scotland show a 38% decline in the first quarter of this year compared with the first three months of last year, but the number of cases, at 1152 between January and March, is evidence that it is still a problem. Measures have been brought in to improve cleaning and hygiene practices, and include the possibility of random inspections, but the levels of both C Diff and MRSA remain worryingly high. A recent NHS survey of more than 2000 people who had recently been in hospital found that standards of cleanliness now cause as much anxiety as the risk attached to operations.

With rates varying widely between hospitals, it is important to identify the factors leading to higher incidence and the effectiveness of measures to combat the bacteria. That is as true of Gartnavel as it is of Vale of Leven - and of every hospital in Scotland.

The Vale of Leven cases were the result of a single outbreak of C Diff, while at Gartnavel they were distributed over a much longer period. Comparing the two may therefore provide significant additional insight.

The terms of reference of the Vale of Leven inquiry have not been set yet. The opportunity to widen its scope should be seized to include the C Diff deaths at Gartnavel (since both are within Greater Glasgow and Clyde health board) with the possibility of also including other Scottish hospitals with a higher than average death rate from C Diff. The point of an inquiry is to learn as much as possible from past mistakes; that requires taking evidence from as many sources as possible.