STAFF absence rates at Oxford City Council are continuing to rise.
In the six months from April to September, almost 8,000 days were lost to sickness.
Council leaders blamed "something inside the culture" for the trend, but have failed to pinpoint the reasons for the problem.
Half-year results showed the council's 1,393 full-time equivalent staff each took an average of 5.71 days off with illness between April and September - up from 5.1 days compared to last year.
And if that trend continued for the remainder of the year, staff absenteeism would be the worst ever at the authority.
Last year, staff each took an average of 11 days off, with the cost put at more than £1m.
This financial year, council managers wanted to bring the figure down to 10.5 days.
A long list of measures has been prescribed in a bid to cure the problem, but no lasting remedy has yet been found.
Last night, city council leader John Goddard said: "It seems to be something inside the culture we have not yet got sorted out.
"It's good local front-line management that is needed - and until that is in place we will stay where we are."
He said that if rates were reduced to an average of eight days a year, savings would pay for an additional 20 staff.
The most common cause of staff sickness given was stress and depression.
Staff in city works, city homes and leisure and culture - the departments responsible for street cleaning, council houses and swimming pools - accounted for the majority of sick days.
Last month, Barton pool and Ferry sports centre were closed because of a lifeguard shortage due to staff sickness.
And a week later, no inflatables could be used during a family fun day at the Ferry pool because it was three lifeguards short.
Labour group leader Bob Price said: "We're unlikely to meet the annual target. It's a significant cost to the council.
"It's disappointing we're still in the same place after all the work that has been done over the last three or four years."
Return-to-work interviews had little impact on sick rates, and private firm Diagnostic Health Services, hired in 2006 to provide a nurse-led call centre-style service for staff phoning in sick, had its contract terminated after it failed to cut absence rates.
City council human resources manager Sue Shutter said: "Our focus has turned to dealing with long-term sickness absence and we will be taking a report to the chief executive on measures to deal with this, particularly where stress is given as the cause."
Mr Goddard added: "There is a connection between good performance, good morale and good health rates.
"As the council's performance improves, I believe morale will continue to rise and this will one day show in reduced sickness rates."
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