Rubuta ci gaba don wannan sakin layi - A wannan shekarar, likitan Biritaniya John Snow, wanda ke aiki a wani yanki mara kyau na London, ya gano gurbataccen ruwa a matsayin hanyar watsa cutar. Bayan barkewar cutar kwalara ta 1854 Broad Street
ya zana taswirar cututtukan kwalara a yankin Soho a London, kuma ya lura da tarin cututtukan kusa da famfon ruwa a wani unguwa. Don ya gwada ra'ayinsa, ya rinjayi ma'aikatan gwamnati su cire makullin famfo, kuma adadin masu cutar kwalara a yankin ya ragu nan da nan. Binciken da ya yi ya sa aka shawo kan annobar. Snow ya kasance memba mai kafa kungiyar Epidemiological Society of London, wanda aka kafa a sakamakon barkewar cutar kwalara a 1849, kuma ana daukarsa daya daga cikin iyayen cututtukan cututtukan cututtukan cututtukan cututtukan cututtukan cututtuka.