Fitch Ratings has affirmed the ratings of Platinum Underwriters Holding Ltd and its subsidiaries and revised the company’s rating outlook to negative from stable.The revision in the outlook reflects Platinum’s recent underwriting performance which has shown significantly greater volatility than expected for a re/insurer in its current rating category, said Fitch.Moreover, the ratings agency said that significant increases in loss estimates from the first half of 2011 recorded in its third quarter 2011 earnings demonstrated challenges that the company faces in measuring and controlling exposure to large losses.Fitch’s ratings recognise that despite the company’s unusually poor performance this year maintained a longer term history of strong underwriting results and profitability and reflected the company’s solid capitalisation, moderate financial and operating leverage, as well as its high-quality and liquid investment portfolio, said the ratings agency.Platinum has an issuer default rating of A- and its subsidiaries have a financial strength rating of A.