Abstract
Bangladesh is a cholera endemic country with a population at high risk of cholera. Toxigenic and non-toxigenic Vibrio cholerae (V. cholerae) can cause cholera and cholera-like diarrheal illness and outbreaks. Drinking water is one of the primary routes of cholera transmission in Bangladesh. The aim of this study was to conduct a comparative assessment of the presence of V. cholerae between point-of-drinking water and source water, and to investigate the variability of virulence profile using molecular methods of a densely populated low-income settlement of Dhaka, Bangladesh. Water samples were collected and tested for V. cholerae from “point-of-drinking” and “source” in 477 study households in routine visits at 6 week intervals over a period of 14 months. We studied the virulence profiles of V. cholerae positive water samples using 22 different virulence gene markers present in toxigenic O1/O139 and non-O1/O139 V. cholerae using polymerase chain reaction (PCR). A total of 1,463 water samples were collected, with 1,082 samples from point-of-drinking water in 388 households and 381 samples from 66 water sources. V. cholerae was detected in 10% of point-of-drinking water samples and in 9% of source water samples. Twenty-three percent of households and 38% of the sources were positive for V. cholerae in at least one visit. Samples collected from point-of-drinking and linked sources in a 7 day interval showed significantly higher odds (P < 0.05) of V. cholerae presence in point-of-drinking compared to source [OR = 17.24 (95% CI = 7.14–42.89)] water. Based on the 7 day interval data, 53% (17/32) of source water samples were negative for V. cholerae while linked point-of-drinking water samples were positive. There were significantly higher odds (p < 0.05) of the presence of V. cholerae O1 [OR = 9.13 (95% CI = 2.85–29.26)] and V. cholerae O139 [OR = 4.73 (95% CI = 1.19–18.79)] in source water samples than in point-of-drinking water samples. Contamination of water at the point-of-drinking is less likely to depend on the contamination at the water source. Hygiene education interventions and programs should focus and emphasize on water at the point-of-drinking, including repeated cleaning of drinking vessels, which is of paramount importance in preventing cholera.
Highlights
Cholera is a life-threatening disease with an estimated 2.9 million cases annually in 69 cholera-endemic countries, including Bangladesh (Ali et al, 2015)
The probability of the presence of V. cholerae O1 [OR = 9.13] and O139 [OR = 4.73] in source water was significantly higher than that in the point-of-drinking water, suggesting that the quality of point-of-drinking water might not be affected by the quality of sources
We found that non-O1/non-O139 V. cholerae was widely distributed throughout both source and point-of-drinking water samples
Summary
Cholera is a life-threatening disease with an estimated 2.9 million cases annually in 69 cholera-endemic countries, including Bangladesh (Ali et al, 2015). In Bangladesh alone, the estimated annual number of cases is 109,000, with a three percent case fatality rate (Ali et al, 2015).Toxigenic and non-toxigenic V. cholerae can cause cholera and cholera-like diarrheal illness and outbreaks. Non-O1/non-O139 and non-toxigenic V. cholerae O1 strains, harboring a range of accessory virulence factors, can cause diarrheal diseases (Morris et al, 1984) and sporadic localized cholera outbreaks (Saha et al, 1996; Faruque et al, 2004; Pang et al, 2007) emphasizing the importance of research on both toxigenic and non-toxigenic V. cholerae. Accessory factors that can cause diarrheal diseases are repeats-in-toxin (rtxA) (Lin et al, 1999; Chow et al, 2001), non-O1 (NAG-ST) and O1 (O1ST) heat-stable enterotoxins encoded by the stn and sto genes, respectively (Ogawa et al, 1990; Dalsgaard et al, 1995; Theophilo et al, 2006), hemolysins encoded by the hlyA gene (Zhang and Austin, 2005; Karlsson et al, 2013), transcriptional activator (toxR) (Waldor and Mekalanos, 1994), hemagglutinin protease encoded by hap (Silva et al, 2006; Mohapatra et al, 2009), ADP ribosylating exotoxin (chxA) (Awasthi et al, 2013), the type VI secretion system (T6SS) (Unterweger et al, 2012), a novel type III secretion system (T3SS) (Dziejman et al, 2005; Shin et al, 2011), and mannose-sensitive hemagglutinin subunit A encoded by mshA (Watnick et al, 1999)
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