The Board That Crossed the Line
A small Dubai café uses one white chopping board for everything. At 10:00 a cook dices raw chicken on it, wipes it with a dry cloth, and at 10:15 slices cucumber and tomato for a salad that will not be cooked. The same knife is used. The cloth is then used to wipe the counter where the salad bowl is placed. At 10:30 a second cook prepares a cheese sandwich on the same counter with unwashed hands after handling the raw chicken tray. The café has colour-coded boards in a cupboard but staff say they are 'too far away'. The salad is served at 11:00 to 14 customers; 6 report diarrhoea 12–36 hours later.
1. Map the cross-contamination routes from the raw chicken to the salad and the sandwich.
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Route 1 - Board and knife (direct): Raw chicken juices remain on the white board and knife. A dry wipe does not remove or kill bacteria; it may spread them. The cucumber and tomato are sliced on the contaminated surface and served raw, so no kill step follows. This is the most direct route.
Route 2 - Cloth (indirect): The cloth picks up contamination from the board and transfers it to the counter where the salad bowl sits. The bowl base and the counter become contaminated, and the cloth may later touch other surfaces.
Route 3 - Hands (indirect): The second cook handles the raw chicken tray, then makes a cheese sandwich without washing hands. The sandwich is RTE, so contamination is consumed directly.
Route 4 - Shared counter (environmental): The counter is a common surface for both the salad and the sandwich, so contamination persists across tasks.
Key point: Every route ends in an RTE food with no subsequent kill step. That is what makes this a high-risk cross-contamination event rather than a nuisance.
2. What separation controls (equipment, layout and workflow) should the café implement?
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Equipment:
- Use colour-coded boards and knives: e.g. red for raw meat, green for salad/vegetables, yellow for cooked meat, blue for fish. Enforce their use - 'too far away' is not acceptable.
- Provide separate cloths for raw and RTE areas, or use single-use paper towels. Launder cloths at high temperature and store dry.
Layout and workflow:
- Designate a raw preparation zone and a RTE zone, physically separated or separated in time with cleaning between.
- Work raw to RTE in a one-way flow where possible; never prepare RTE food on a surface just used for raw meat.
- Store raw foods below and away from RTE foods in the chiller.
Behaviour:
- Wash hands and change gloves between raw and RTE tasks.
- Clean and sanitise the board, knife and counter between tasks - a dry wipe is not cleaning.
- Supervise and verify: spot-check board colour use during service.
3. The café says the salad was 'probably fine because it was washed'. Explain why washing does not solve this problem.
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Washing removes soil and some surface contamination, but it does not sterilise. Two limits:
- Washing happens before the contamination event. The cucumber and tomato were presumably washed, then sliced on a contaminated board. The contamination is added after washing, so washing provides no protection.
- Washing cannot remove bacteria that have been transferred onto cut surfaces. Once the knife carries bacteria into the flesh of the cucumber, surface washing is irrelevant - and the salad is not washed again after slicing.
Correct principle: For RTE food, the control is prevention of contamination, not removal after the fact. That means clean and sanitised surfaces, colour-coded equipment, and handwashing - not a reliance on washing the ingredient.
Additional point: Even if the salad were re-washed, the water itself can become a contamination vehicle if not managed, and the salad would still be served raw with no kill step.