Bermuda reinsurer Platinum Underwriters Holdings Ltd reported a net fourth-quarter loss of $17.7 million as it was hit by $78 million in catastrophe losses.The company estimated losses of $68.2 million relating to the New Zealand earthquake and $9.9 million relating to the Australian floods, which accounted for the bulk of the $108.5 million fall in quarterly net income.There has been further catastrophe activity in Australia this year, which will impact first quarter results in the range of $15 million to $30 million, Platinum estimated.More flooding occurred in large areas of Australia and Cyclone Yasi made landfall in Northern Queensland.Platinum posted a full-year profit of $215.5 million a fall of 43.8 percent.The results for the quarter include net premiums earned of $185 million, net favourable development of $27.7 million, net investment income and net realised gains on investments of $38.9 million.Michael Price, president and chief executive officer of Platinum, said: “2010 was a difficult year for underwriting and investing with heavy catastrophe losses and volatile interest rates.“Despite these challenges, Platinum had an acceptable year, producing double-digit returns and growth in book value per share for the year.“Our book value per common share was $50.20 as of December 31, 2010, an increase of 11 percent for the full year.“Despite the prevailing soft market conditions, we expect to participate selectively in a variety of reinsurance classes while maintaining our strategy of underwriting for profitability, not market share, and continuing to align our capital base with business opportunities.”The company’s combined ratio for the quarter - the percentage of premium dollars spent on claims and expenses was 107.8 percent for the fourth quarter and 80.6 percent for the full year.Shareholders’ equity was $1.9 billion as of December 31, 2010, a decrease of $182.3 million (or 8.8 percent) from $2.08 billion as of the end of 2009.Book value per common share was $50.20 at year-end 2010, an increase of $4.98 (or 11 percent) from $45.22 a year earlier.During the fourth quarter, the company repurchased more than 1.68 million shares for approximately $75.1 million.During the year, they bought back 9.67 million shares for $379.7 million.