The first reported outbreak of an undetermined species of human infection with spotted fever group Rickettsia in Lu'an, China

•This was the first reported outbreak of an undetermined species of a human infection with the spotted fever group of Rickettsia in China.•In this outbreak, the clinical manifestations of the cases were similar to those of Rocky Mountain spotted fever and Japanese spotted fever; however, the severity was significantly lower than these diseases.•This study showed that C-reactive protein and the numbers of neutrophils by blood testing showed an increasing trend in different periods, while lymphocyte ratios and platelets showed a decreasing trend.•Our findings have also shown that the cases we discovered might only be “the tip of the iceberg”.