Work to clean up a hospital bacteria outbreak inadvertently led to more contamination, new documents reveal.
Brain surgery was postponed at Edinburgh's Western General in March after a small number of patients contracted the Pseudomonas aeruginosa bug from showers and taps in a ward.
A decontamination programme was ordered by NHS Lothian.
But documents released by health watchdogs show this work is believed to have caused further problems.
Health Protection Scotland (HPS) papers show a shower in the hospital's department of clinical neurosciences twice tested negative for the bacteria following the outbreak, and patients were allowed to keep using it.
But later tests on the shower were positive for Pseudomonas aeruginosa - a common bacteria that can be harmful to patients who are very vulnerable to infection - and it was taken out of service.
HPS reports, released after a Freedom of Information request, show the "current hypothesis is that remedial plumbing, extensive flushing and water pressure may have dislodged biofilm (a collection of microorganisms such as bacteria) within the water systems leading to the contamination in the recent samples".
NHS Lothian said it followed national testing guidelines and the dislodging of the biofilm did not lead to any further patient infections. It added that once the bug was identified, it was immediately taken out of use.
The department of clinical neurosciences had been due to move into the new children's hospital in July but that move was postponed due to safety fears about the new complex and it is not expected to move there until spring next year.
Tom Waterson, Scotland health committee chair at trade union Unison, said: "The outbreak was a concern for patients and staff alike.
"They have been desperate to leave that facility because it is in dire need of modernisation and they were meant to have moved out of there months ago.
"My concern is that we now know there had been doubts about the move to the new building for a long time so why was there not more done on the maintenance of the neuroscience department."
The Scottish government has said it will provide about £6m in funding to help keep the existing Sick Kids hospital and neuroscience department up to scratch until the new facility is open next year.
A total of 47 patients had elective procedures cancelled and rearranged as a result of the March outbreak.
Further positive samples for the bug were identified in July and since then 18 samples (out of 2,926 taken) have tested positive for what the health board described as "very low counts of Pseudomonas aeruginosa".
A spokeswoman for NHS Lothian said: "The water sampling regime used is a national protocol for assessing Pseudomonas aeruginosa regardless of how the bacteria entered the water.
"As part of that protocol, outlets continue to be tested after remedial works have been carried out.
"On identification of Pseudomonas aeruginosa in shower water, the shower was immediately removed from patient use so that no patient exposure could occur."
It is not known what happened to the patients who contracted the bug in March as NHS Lothian said it was "unable to discuss individual patients and their outcomes".