Cholera returns to southern Vietnam in an outbreak associated with consuming unsafe water through iced tea: A matched case-control study

Abstract

BackgroundAfter more than a decade of steadily declining notifications, the number of reported cholera cases has recently increased in Vietnam. We conducted a matched case-control study to investigate transmission of cholera during an outbreak in Ben Tre, southern Vietnam, and to explore the associated risk factors.Methodology/Principal findingsSixty of 71 diarrheal patients confirmed to be infected with cholera by culture and diagnosed between May 9 and August 3, 2010 in Ben Tre were consecutively recruited as case-patients. Case-patients were matched 1:4 to controls by commune, sex, and 5-year age group. Risk factors for cholera were examined by multivariable conditional logistic regression. In addition, environmental samples from villages containing case-patients were taken to identify contamination of food and water sources. The regression indicated that drinking iced tea (adjusted odds ratio (aOR) = 8.40, 95% confidence interval (CI): 1.84–39.25), not always boiling drinking water (aOR = 2.62, 95% CI: 1.03–6.67), having the main source of water for use being close to a toilet (aOR = 4.36, 95% CI: 1.37–13.88), living with people who had acute diarrhea (aOR = 13.72, 95% CI: 2.77–67.97), and little or no education (aOR = 4.89, 95% CI: 1.18–20.19) were significantly associated with increased risk of cholera. In contrast, drinking stored rainwater (aOR = 0.17, 95% CI: 0.04–0.63), eating cooked seafood (aOR = 0.27, 95% CI: 0.10–0.73), and eating steamed vegetables (aOR = 0.22, 95% CI: 0.07–0.70) were protective against cholera. Vibrio cholerae O1 Ogawa carrying ctxA was found in two of twenty-five river water samples and one of six wastewater samples.Conclusions/SignificanceThe magnitude of the cholera outbreak in Ben Tre was lower than in other similar settings. This investigation identified several risk factors and underscored the importance of continued responses targeting cholera prevention in southern Vietnam. The association between drinking iced tea and cholera and the spread of V. cholerae O1, altered El Tor strains warrant further research. These findings might be affected by a number of limitations due to the inability to capture asymptomatic or mildly symptomatic infections, the possible underreporting of personal unhygienic behaviors, and the purposive selection of environmental samples.

Individual and Household Risk Factors for Symptomatic Cholera Infection: A Systematic Review and Meta-analysis

“…The majority of studies were both age- and sex-matched analyses, but a subset assessed risk for cholera based on these characteristics. Fifteen studies assessed differential risk by age [ 13 , 26 , 32 , 33 , 35 , 47 , 53 , 70 , 82 , 85 , 97 , 101 , 104 , 110 , 118 ], 10 of which implemented a multivariable model [ 26 , 32 , 33 , 35 , 82 , 97 , 101 , 104 , 110 , 118 ]. Age was measured heterogeneously and findings were mixed.…”

Individual and household exposures associated with cholera transmission in case–control studies: a systematic review

“…Water-related transmission in the public domain included consuming ice [49,83,94,95], drinks from street vendors [56,67,69,78], and/or drinking water from a community well, river, or lake [38,44,59,69,73,85,[90][91][92]95], drinking from a municipal water supply [39,78,95]. Bathing or using well, river or lake water was also identified as a risk factor [38,70].…”

“…In 53% of studies that assessed water-related exposures, there was at least one significant water-related exposure where the transmission domain could not be determined. This was most often because treating water (by boiling, chlorine or unspecified) in the home could eliminate contamination from either domain [8,39,49,50,52,56,58,68,76,78,86,87,94,96]. Several of these studies also presented evidence of significant public domain transmission, suggesting that even if household transmission could not be determined, public transmission was likely present [39,49,50,78,94].…”

Food Hygiene Surveillance in Italy: Is Food Ice a Public Health Risk?

“…In developing countries where hygiene and health conditions are considered to not be optimal and cholera is spread in its endemic form, the consumption of food coming into contact with ice was shown to be an important risk to human health. In these geographical areas, the consumption of beverages produced and purchased by street-food and food businesses not constantly subject to specific controls performed by the health authorities contributes to an increasing transmission risk of foodborne diseases [12,23,24].…”

“…and Salmonella spp. in Greece [8,9]; Salmonella Saintpaul in Australia [10]; multi-antibiotic-resistant strains such as Escherichia coli ESLB (extended-spectrum-beta-lactamase) in Vietnam; and some episodes of cholera related to Vibrio cholerae O1 Ogawa ctxA have been linked with ice melted in tea [11,12].…”