A cholera outbreak caused by drinking contaminated river water, Bulambuli District, Eastern Uganda, March 2016

BMC Infectious Diseases

Table 3 Case-control study: risk factors for cholera due to water utility or drinking water from various water sources (n = 100 Cases, n = 100 controls)

Variable	Cases n (%)	Controls n (%)	OR_M-H^a	95%CI
Untreated borehole water for drinking
Yes	35(36)	54(54)	0.31	0.13-0.65
No	63(64)	46(46)	ref	0.13-0.65
Untreated Cheptui river water for drinking
Yes	76(78)	54(51)	7.8	2.7-22.0
No	22(22)	49(49)	ref	2.7-22.0
Untreated swamp water for drinking
Yes	11(11)	5(5)	2.5	0.80-8.0
No	87(89)	95(95)	ref	0.80-8.0
Untreated borehole water for domestic utility
Yes	35(36)	40(40)	0.70	0.30-1.5
No	63(64)	60(60)	ref	0.30-1.5
Untreated Cheptui river water for domestic utility
Yes	81(83)	69(69)	3.8	1.4-10.0
No	17(17)	31(31)	ref	1.4-10.0
Untreated swamp water for domestic utility
Yes	12(12)	3(3)	5.5	1.2-25.0
No	86(88)	97(97)	ref	1.2-25.0

^aORM_-H odds ratio of association was computed by stratification or Mantel-Haenszel method. Drinking untreated borehole water was protective, OR_M-H = 0.31, 95% CI=0.13-0.65) and this result might be due to confounding factors in which persons may have used bore hole water with other water sources in various combinations. Water was drunk or used untreated (and unboiled) from all sources. People who drank untreated Cheptui river water were up to 8 times as likely to have had cholera compared to those who did not (OR_M-H =7.8, 95% CI = 2.7-22.0) and this relatively larger OR_M-H value supports the water borne hypothesis. People who used untreated Cheptui river water for routine work were up to 4 times as likely to have had cholera compared to those who did not (OR_M-H =3.8, 95% CI = 1.4-13.0)

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