Effectiveness of common and improved sanitary washing methods in selected cities of West Africa for the reduction of coliform bacteria and helminth eggs on vegetables

To analyse and improve the effectiveness of common indigenous washing methods for the reduction of faecal coliform (FC) populations on the surface of wastewater-irrigated vegetables and to determine simple factors affecting their efficacy. Questionnaire interviews were used to gather information on common methods used for washing vegetables in seven West African countries. The efficacy of the most common decontamination methods was measured in terms of log reductions in FC populations on homogenised contaminated lettuce, cabbage and spring onion samples. The large majority of urban households and restaurants in the subregion are aware of vegetable-related health risks and wash vegetables before consumption. Methods used vary widely within and between Ghana and neighbouring francophone West African countries. However, several of the most common methods do not reduce the contamination to any desirable level. Significantly, different log reductions are achieved depending on the washing method, contact time and water temperature. Tests to improve the apparent ineffective methods were especially promising in view of the relatively expensive vinegar. However, up to 3 log units reduction is also possible at a much lower price with 'Eau de Javel' (household bleach), which is commonly used in francophone West Africa. Washing vegetables before consumption is an important component of a multiple barrier approach for health risk reduction. The high risk perception among consumers demands that more information be made available on the appropriate use of these washing methods. Any washing method will need complementary efforts to reduce contamination before the vegetables enter the kitchen, such as safer irrigation practices.