Five poultry workers have been infected with H5N1 bird flu while working at a farm in northeast Colorado, an unusual cluster of human cases though only mild symptoms have been reported, according to state and federal officials. The Colorado Department of Public Health reported the first three cases on Friday and confirmed two more on Sunday night. All of them were involved with the culling of poultry at a commercial egg laying operation where animals were infected with H5N1. Those infected reported mild symptoms, including conjunctivitis (pink eye) and common respiratory infection symptoms, wh…