Rubuta ci gaba ga wannan sakin layi - Cutar Soho a London a 1854
ya ƙare bayan likita John Snow gano unguwa Broad Street famfo kamar yadda gurbata da kuma shawo kan jami'an cire ta rike. Snow ya yi imanin cewa ruwa mai gurɓataccen ƙwayoyin cuta shine tushen kwalara, maimakon ƙwayoyin cuta a cikin iska (wanda ake kira "miasmata"). Binciken da ya yi ya nuna cewa gurɓataccen ruwa shi ne ainihin abin da ke yaɗa cutar kwalara, ko da yake bai gano abin da ya gurɓata ba. Ko da yake Filippo Pacini ya ware "Vibrio cholerae" a matsayin mai haddasa cutar kwalara a wannan shekarar, zai ɗauki shekaru da yawa kafin ka'idar miasma ta faɗi.