set_worst_disease_effect

set_worst_disease_effect = {
	if = {
		limit = { has_trait = bubonic_plague }
		save_scope_value_as = {
			name = disease_type
			value = flag:bubonic_plague
		}
	}
	else_if = {
		limit = { has_trait = cancer }
		save_scope_value_as = {
			name = disease_type
			value = flag:cancer
		}
	}
	else_if = {
		limit = { has_trait = smallpox }
		save_scope_value_as = {
			name = disease_type
			value = flag:smallpox
		}
	}
	else_if = {
		limit = { has_trait = measles }
		save_scope_value_as = {
			name = disease_type
			value = flag:measles
		}
	}
	else_if = {
		limit = { has_trait = dysentery }
		save_scope_value_as = {
			name = disease_type
			value = flag:dysentery
		}
	}
	else_if = {
		limit = { has_trait = ergotism }
		save_scope_value_as = {
			name = disease_type
			value = flag:ergotism
		}
	}
	else_if = {
		limit = { has_trait = consumption }
		save_scope_value_as = {
			name = disease_type
			value = flag:consumption
		}
	}
	else_if = {
		limit = { has_trait = typhus }
		save_scope_value_as = {
			name = disease_type
			value = flag:typhus
		}
	}
	else_if = {
		limit = { has_trait = great_pox }
		save_scope_value_as = {
			name = disease_type
			value = flag:great_pox
		}
	}
	else_if = {
		limit = { has_trait = pneumonic }
		save_scope_value_as = {
			name = disease_type
			value = flag:pneumonic
		}
	}
	else_if = {
		limit = { has_trait = leper }
		save_scope_value_as = {
			name = disease_type
			value = flag:leper
		}
	}
	else_if = {
		limit = { has_trait = gout_ridden }
		save_scope_value_as = {
			name = disease_type
			value = flag:gout_ridden
		}
	}
	else_if = {
		limit = { has_trait = ill }
		save_scope_value_as = {
			name = disease_type
			value = flag:ill
		}
	}
}

As written in game/common/scripted_effects/20_health_effects.txt.