HAMBURG (AFP) - An outbreak of killer E. coli that has spread to 12 countries and killed 19 people may be linked to a Hamburg festival in May and could have caused a 20th death, according to reports on Saturday. As authorities continued to hunt the source of the killer bug, Germany's national disease centre, the Robert Koch Institute (RKI), is looking closely at a harbour festival that took place in Hamburg on May 6-8. The weekly newspaper Focus said Saturday the festival drew 1.5 million visitors from Germany and abroad and noted that the first reported case of E. coli infection followed just a week later in the city's university hospital.