Activity in China’s factory sector contracted in January for the first time in more than two years, an official survey showed, a far worse result than expected that will add to worries about the country’s choppy economic outlook this year. The official Purchasing Managers’ Index (PMI) fell to 49.8 in January from December’s 50.1, the National Bureau of Statistics said on Sunday, a whisker below the 50-point level that separates growth from contraction on a monthly basis.