This study evaluated the development of soft rot disease (Janthinobacterium agaricidamnosum) in Agaricus bisporus crops. Symptoms of the disease appeared at the end of the first break of the mushroom’s harvest and mostly occurred in the later stages of cultivation (in the second break and between the 1st and 2nd crop). Distribution of lesions in growing rooms indicated that employees served as a vector of disease infection, which was spread when harvesting the mushrooms. An evaluation of the post-harvest mushrooms showed that fruiting bodies, especially those stored in closed containers, showed disease symptoms when infected at harvest.