TOKYO, Dec 17 - Japan's Nikkei average closed down 1.74 percent on Wednesday after Taiwan said a medical researcher had tested positive for SARS, prompting investors to unload Nippon Yusen <9101.T> and other shipping and airline shares. "It is only one person so it is unclear if we are facing a problem like earlier this year," said Makoto Suzuki, a fund manager at Chuo Mitsui Asset Management. "But with China so important to the world economy, the potential implications are large." The Nikkei <.N225> ended down 1.74 percent or 178.96 points at 10,092.64, extending the previous session's 2.09 percent decline. The broader TOPIX index <.TOPX> shed 1.48 percent or 14.87 points to a one-week low of 989.95. During the midsession break in Tokyo, Taiwan's Department of Health said a 44-year-old SARS researcher at a military hospital had tested positive for the deadly virus and was probably infected in the laboratory where he worked.//