A continuing rise in negative home equity and unemployment has led to rating actions on 581 prime RMBS transactions issued between 2005 and 2008, Fitch Ratings said.

"While actual loan losses to date remain low on average for the transactions reviewed (36 basis points), average delinquency has almost doubled since the start of the year to 11% and continues to grow due to high average roll-rates from performing to delinquency," Fitch said in a report.

About 45% of the borrowers in the private-label MBS reviewed by Fitch owed more on their mortgages than their homes were worth, according to Grant Bailey, a senior director at the rating company.

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