Immediately after the devastating earthquake in Turkey in August 1999, an infectious disease surveillance system was established in Kocaeli Province (the biggest area affected). This surveillance study was mainly focused on diarrheal diseases. During a 33-day period, 1,468 stool cultures were processed. Diarrheal diseases increased step-by-step and later decreased to the initial level by the end of this period. Cases were scattered throughout the entire region, and the identified causes were various, indicating a multifocal increase. Of the identified causes, Shigella species were the most common. Nevertheless, Shigella isolates also belonged to distinct serotypes and clones. This study indicated a multifocal, multiclonal increase in diarrheal diseases after this massive disaster, thus indicating the necessity to set up infectious disease surveillance systems after such events.