In October 2003, Tong Zeng, a Chinese lawyer and a volunteer in a 1998 Chinese-American medical cooperation program, published a book[16] that again speculated that SARS could be a biological weapon developed by the United States against China. In the book, Tong disclosed that in the 1990s, many American research groups collected thousands of blood and DNA samples and specimens of mainland Chinese (including 5,000 DNA samples from twins) through numerous joint research projects carried out in China. These samples were then sent back to the United States for further research, and could be used in developing biological weapons targeting Chinese. These samples came from 22 provinces in China, all of which were hit by SARS in 2003. Only provinces like Yunnan, Guizhou, Hainan, Tibet, and Xinjiang were left out, and all these provinces suffered less severely during the SARS outbreak. The author suspects that Japan is also involved, as many Japanese factories in Guangdong in the 1990s made it compulsory for all workers to have blood tests in the factory annually, rather than asking workers to go to local hospitals for blood tests and a proper physical examination. However, Tong Zeng admits that these are only speculations, and he does not have any concrete proof from the study of the virus's genetic sequence.[17]