Evaluation of an Emergency Bulk Chlorination Project Targeting Drinking Water Vendors in Cholera-Affected Wards of Dar es Salaam and Morogoro, Tanzania

The Ministry of Health, Community Development, Gender, Elderly and Children (MoHCDGEC) of Tanzania first reported an outbreak of cholera in Dar es Salam region in August 2015.1 By February 2016, the outbreak had affected 22 of 25 mainland regions in Tanzania and resulted in 16,521 cases and 251 deaths. Urban areas of Dar es Salaam and Morogoro were heavily affected. Dar es Salaam reported 4,714 cases (29% of the mainland total), and Morogoro reported 1,325 cases (8% of the mainland total).2 Provision of safe drinking water is essential during cholera outbreaks, and chlorination of drinking water supplies is a high priority in both urban and rural settings. During a cholera outbreak, the World Health Organization (WHO) recommends free residual chlorine (FRC) levels of at least 0.5 mg/L at the point of use, 1.0 mg/L at tap stands, and 2.0 mg/L at tanker truck filling.3 In addition, routine monitoring of FRC levels is important to ensure the continued provision of safe water.4 Recent systematic reviews of water, sanitation, and hygiene (WASH) responses during cholera outbreaks and emergencies highlighted that water quality interventions implemented during outbreaks and emergencies have not been well documented.5–7 Distribution of chlorine-based household water treatment products is common during cholera outbreaks, and has been shown to improve the microbiological quality of water when paired with appropriate training and follow-up by community health workers.8,9 Community-level chlorination interventions implemented during cholera outbreaks are not well documented in the literature, with the exception of well chlorination programs.6,10–13 At the start of the outbreak, the municipal drinking water utilities in Dar es Salaam and Morogoro estimated that only 8–20% of the residents had in-home piped water connections.14 The remainder of residents obtained drinking water from a variety of sources, including private water vendors who sold water from large tanks that ranged in volume from 1,000 to 20,000 L. Vendors sold water in 20-L increments to nearby community members. Vendors sold water piped directly from the utility, water pumped from private boreholes, or water delivered by water trucks. The water sources for the trucks varied. Some collected water at utility truck filling stations, whereas others collected from other sources such as boreholes. In addition, some residents collected water from boreholes, shallow hand-dug wells, and rainwater. Multiple challenges compromised the drinking water supply in both Dar es Salaam and Morogoro. First, although water supplied by the utilities was chlorinated, FRC levels throughout the piped network were inconsistent. Second, vendor tanks and trucks that filled from boreholes were not chlorinated. Third, trucks that filled from utility filling stations did not receive booster chlorination doses. At the peak of the outbreak and at the baseline of this program, spot checks from the piped water system, water trucks, and vendor tanks in Dar es Salaam resulted in detection of low levels of FRC. Free residual chlorine was detected in 36% (12/33) of samples from the piped water system, 53% (10/19) of samples from water trucks, and 12% (32/266) of samples from vendor tanks. Of the 32 samples from vendor tanks with detectable FRC, 24 samples were from tanks that filled from the piped water system and eight samples were from tanks that filled from water trucks. Morogoro district had similar issues with the piped utility and borehole water. In response to the chlorination challenges observed in Dar es Salaam, Morogoro, and other regions, the government of Tanzania and partners took several steps: first, advocacy to municipal water utilities to increase chlorine levels to standards recommended during cholera outbreaks; second, strengthening the monitoring of the municipal distribution systems; third, distribution of household water treatment products to households in cholera hot spots; fourth, closure of shallow hand-dug wells; and fifth, social mobilization activities. However, few steps were taken to address the insufficient levels of chlorine in bulk drinking water supplies sold by private water vendors. The emergency bulk chlorination program targeting vendors in cholera-affected wards in Dar es Salaam and Morogoro aimed to address this gap, and started with a small pilot test in February 2016. Promising results led to expansion of the program.15 The emergency bulk chlorination program was a collaborative project between the U.N. Children’s Fund (UNICEF), Tanzania, the MoHCDGEC of Tanzania, and the US Centers for Disease Control and Prevention (CDC). MoHCDGEC and UNICEF implemented the program, and the CDC set up the monitoring and evaluation system. The program targeted large-volume water vendors in the 15 wards of Dar es Salaam and eight wards of Morogoro with the highest cholera attack rates at the start of the 2015 outbreak. At the start of the program, ward environmental health officers were trained to identify, map, and enroll vendors with tanks of at least 1,000 L in volume into the bulk chlorination project. Ward officers conducted a baseline assessment, and vendors were invited to an orientation where they received project information and dosing instructions for the 8.68-g sodium dichloroisocyanurate (NaDCC) tablets (herein referred to as chlorine tablets), based on the specific volume of their tank(s). Each tablet contains 5 g of available chlorine, and the applied dose was approximately 1.0 mg/L. During pilot testing, this dose resulted in an FRC level of approximately 0.7 mg/L, 30 minutes after treatment. Vendors were trained to place tablets in tanks during or before tank filling to ensure proper mixing. Ward officers assigned to each of the targeted wards distributed the chlorine tablets to vendors and conducted routine monitoring visits at vendor locations throughout the 3-month program. Each vendor who continued in the program received at least a 3-month supply of chlorine tablets free of charge. In addition, the project allowed any non-mapped vendors or institutions in these wards, who expressed interest, to enroll at any time. In the fall of 2016, approximately 3 months after the first chlorine tablet distribution, the bulk chlorination program was evaluated in all implementation wards of Dar es Salaam and Morogoro.