The number of borrowers in arrears on their home loans in some areas may not improve, leaving lenders facing losses, an analysis by Fitch Ratings of loan delinquencies suggests.Fitch said that across Australia delinquencies increased to 1.45 per cent at 31 March 2013, up 25 basis points from 1.2 per cent at 30 September 2012, but below the five-year average of 1.53 per cent.Regions south west of Sydney, west of Melbourne and south of Brisbane - where serviceability is key to mortgage performance - experienced the sharpest increases in arrears, Fitch said.Arguing that "delinquency floors exist", Fitch said that "Christmas spending and the increasing cost of living may have arguably offset the positive benefits from lower mortgage rates, but do not fully justify the increase in delinquency rates." "The increasing number of delinquent borrowers in low-income and high-unemployment regions could indicate that these specific serviceability constraints cannot be fully solved by monetary policy. "Therefore, the delinquency rate in these regions may have reached a virtual floor at end-September 2012."Fitch noted that RBA cuts in the cash rate "did not have a positive impact on mortgage performance in the six months to end-March 2013, in contrast to the six months to end-September 2012."Nelson Bay in New South Wales - which includes the localities of Corlette, Fingal Bay and Shoal Bay - remained the worst performing postcode by value of mortgages in arrears, Fitch said, with 6.6 per cent of mortgages delinquent at the end of March 2013.Fitch said Nelson Bay has been the worst performing postcode in Australia since postcode-level analysis was first published, in November 2007. Other problem postcodes are Montrose in Tasmania, Waterford and Surfers Paradise in Queensland, and Rooty Hill and Green Valley in NSW.Thirteen of the 20 worst performing postcodes were in New South Wales, and eight of these were in south west and western Sydney.