A Zumba class and photo session were underway when gunfire erupted, hitting four people including a 13-year-old girl, inside a Back of the Yards dance studio Monday night. Two separate groups began firing about 8:30 p.m. in the 1500 block of West 51st Street, causing dancers and witnesses inside the Body Factory Nutrition to run for cover, Chicago police said. When police responding to several reports of gunfire got there, five witnesses told officers they were "in the middle of their Zumba class when bullets came through the front windows, striking their friends," according to a police report. Additional victims who were taking a photo heard loud bangs and "immediately ran to back of the dance studio," according to the report. The wounded — a man, a girl and two women — ranged in age from 13 to 57. The 13-year-old girl, who was shot in the lower back, was taken to Comer Children’s Hospital in fair condition. A 29-year-old man, who was shot in the neck, was taken to the University of Chicago Medical Center in good condition, police said. Additionally, a 48-year-old woman was shot in her left arm. She was also taken to U of C in good condition, and a 57-year-old woman who was shot in the right hand was taken to St. Bernard Hospital, police said. Multiple shell casings, including ones from at least one rifle, were found at 5114 S. Laflin St., the report said. A Cadillac, a nearby building and a city utility truck were damaged. The victims were the unintended targets of the attack. Area One detectives are investigating. No arrests have been made.