An increasing number of Australian housing loans are in arrears - a trend that continued for a fifth consecutive month in March for prime residential mortgage-backed securities, as measured by Standard & Poor's Performance Index. The upward trend in arrears was not consistent across all product types, however, according to S&P Global Ratings.The S&P prime RMBS SPIN increased to 1.13 per cent in March from 1.11 per cent in February, while the SPIN for low-documentation loans fell 14 basis points in March to 4.41 per cent, with part of the decline reflecting a rise of around two per cent in outstanding loan balances. Low-doc loans represent around 1.3 per cent of total loans outstanding that underlie prime RMBS transactions, down from a peak of 13.2 per cent in January 2008.The SPIN for nonconforming loans fell to 4.08 per cent in March from 5.22 per cent the previous month, helped by a 28 per cent increase in outstanding loan balances during the month.Against this general trend, Fitch Ratings affirmed its ratings for around A$130 million in debt securities issued by La Trobe Financial Capital Markets Trust 2015-1's floating-rate Class A notes. The issue consists of notes backed by Australian non-conforming residential mortgages originated by La Trobe Financial Services Pty Limited. At 31 March 2016, the transaction's 30-plus days in arrears level, at 4.01 per cent, tracked below Fitch's 4Q15 Non-Conforming RMBS Index of 5.69 per cent."There have been no losses for the transaction since issuance," Fitch noted in a media release.