Washed microbiota transplantation for patients with 2019‐nCoV infection  Other: washed microbiota transplantation, other: placebo  China/COVID‐19 complicated with refractory intestinal infections  0, all, 14–70 complicated with refractory intestinal infections  Treatment  Experimental: observational group 5 u washed microbiota suspension administered via nasogastric tube, nasojejunal tube or oral, combining with standard therapy