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Microbe of the Month: Heat, meat and squalor: a recipe for disaster: When a US restaurant ignored basic health rules, 800 fell ill with salmonella poisoning. Bernard Dixon reports

AT A TIME of the year when we need to be reminded of the hazards of food-borne disease, the journal Epidemiology and Infection has just published a gripping analysis of the largest outbreak of salmonella food poisoning ever reported, in South Carolina. Indeed, with more than 800 people becoming ill, this was one of the worst incidents of its sort on record anywhere. And it could easily have been avoided.

'Restaurant A' came under suspicion at the beginning of September 1990 when the state health authorities received reports of two people who had been admitted to hospital with severe salmonellosis. An infection of the bowel by salmonella bacteria, this causes diarrhoea, fever and abdominal pain. Often a relatively trivial (though debilitating) illness that clears up after a few days, salmonellosis can also be much more serious, rivalling typhoid fever in its severity.

In this case, both of the hospitalised victims were shopkeepers who had attended a convention of 2,000 hardware retailers over the previous weekend. Restaurant A had catered for the event in the convention centre. Phone calls from the South Carolina Department of Health and Environmental Control to hardware stores around Greenville established that other people had suffered diarrhoea after the event. An investigation was clearly necessary.

Investigators set out to contact every sixth name from a list of convention participants. They reached 398 (98 per cent) of them, and found that 135 (34 per cent) of these had been ill - giving an estimated 800-plus victims in all. Answers to questions about various meals consumed during the weekend soon pinpointed turkey served for lunch on Sunday 26 August as the principal source of infection. Although it was too late to examine any of the turkey, tests on the faeces of a number of victims who provided samples indicated that Salmonella agona had been responsible for the outbreak.

In one sense, the incrimination of Restaurant A came as no surprise, because at least 23 health and hygiene violations had occurred there during the first six months of 1990 alone. The offences had led to repeated withdrawals of the establishment's high-quality rating, which had been reinstated after successive, though temporary, improvements.

Once the investigators began to study the background to the latest incident, they uncovered a further, unbelievable story of irresponsibility and squalor. First, the refrigerators, ovens and other equipment in the kitchen, while adequate for the 200-300 meals that were prepared each day during normal business, were inappropriate for the task of producing a further 7,000 meals during the 30 hours of the convention.

Second, turkey had been handled without any regard for the fact that bacteria multiply rapidly on any sort of meat left at room temperature. Contamination of poultry with strains of salmonella is by no means uncommon, but the associated dangers can usually be contained by appropriate cooking, refrigeration and kitchen procedures. Turkey and chicken should be thoroughly cooked. There should be no opportunity for raw poultry to contaminate cooked meat, utensils or surfaces; and cooked poultry must be refrigerated if not served immediately.

In this case, 92 frozen turkey breasts were delivered to the restaurant on Friday 24 August. An employee confirmed that about 20 of these, cooked but not boned, were sitting unrefrigerated on a preparation table when he came on duty at 7am on Saturday. There they remained, with work going on all around, at least until he left at 5pm. An unrefrigerated truck took the other 72 breasts to an associated restaurant - a journey of about an hour. After being cooked on the Saturday, they were reloaded on Sunday morning on to the same truck, which broke down en route back to South Carolina and was abandoned by the roadside. An hour later, another unrefrigerated truck picked up the breasts and returned them to Restaurant A. The temperature was 27C.

Restaurant staff warmed the turkey for serving at the convention by reheating the water in which it had originally been boiled and pouring this over the breasts. Waiters setting out the buffet then noticed that much of the turkey had an offensive odour, and returned more than half of the pieces to the kitchen with a request for replacements. But as no further breasts were available, the kitchen personnel rinsed the turkey under a cold tap, rewarmed it under the hot tap, and sent it back to the convention centre, where it was served.

In reporting this sequence of events, the investigators expressed dismay over a health department's inability to improve sanitary practices in a restaurant that had repeatedly failed inspections. Yet they disregarded an equally perplexing feature of the story. Although diners were not asked about taste or odour, no fewer than 213 mentioned that they had eaten turkey that smelt or tasted bad. Now why on earth should they do that?