Since 2007, there has been an increase in reported cases of FTLS in Xinyang City, Henan Province. These patients were tentatively diagnosed as having A. phagocytophilum infection. However, only a few (8.4%, 24/285) such patients had evidence for A. phagocytophilum infection, and none of the 285 patients tested positive for the many other pathogens capable of causing similar clinical and laboratory manifestations that were also investigated. These findings suggested novel infectious agents, including viruses.