General outbreaks of infectious intestinal diseases linked with private residences in England and Wales, 1992-9: questionnaire study

Methods and results

After initial outbreaks of infectious intestinal disease in England and Wales the centre obtained data via a standard, structured questionnaire (response rate >80%)2 and stored it in a dynamic database derived from EpiInfo version 5. We selected outbreaks linked with private households and analysed them with Microsoft Excel and Stata version 6. Relative proportions of outbreak settings and types were compared using the χ² test.

General outbreaks in the home (figure) accounted for 226 (5%) of the 4604 outbreaks reported during the surveillance period; of 4602 people affected, 205 (4.5%) were admitted to hospital. The risk of hospitalisation from outbreaks linked to the home was higher than that linked with outbreaks related to other premises (0.045 v 0.016; risk ratio 2.66; 95% confidence interval 2.31 to 3.06).

Foodborne outbreaks of infectious intestinal disease linked with the domestic setting and laboratory reports of salmonellosis in England and Wales. Source: PHLS salmonella dataset

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Food was the predominant transmitter of infectious intestinal disease (192/226; 85%); person to person transmission (13; 6%) and waterborne transmission (3; 1%) accounted for some of the remainder. The mode of transmission was unknown in 9 (4%) outbreaks. Foodborne transmission was linked to social functions—for example, barbecues and dinner parties—more frequently than other modes of transmission were (169/192 (88%) v 17/34 (50%); χ²=28.5, df=1, P<0.001). The mean size of group affected was 20 people (range 2 to 224, median 12, mode 8). The most frequently reported pathogen was salmonella (147/192; 77%); Clostridium perfringens (9; 5%), Norwalk-like virus (8; 4%), and Vero cytotoxin producing Escherichia coli O157 (3; 2%) featured less often. Poultry (59/207; 29%), desserts (37; 18%)—which often contained raw egg—and egg dishes (35; 17%) were commonly implicated; the link between these food vehicles and salmonella is well understood.3 The most common faults in food hygiene were inappropriate storage, inadequate cooking, and cross contamination (99/251, 39%; 78, 31%; and 51, 20%, respectively); in each case salmonella was reported more frequently than any other pathogen (84/99, 85%; 67/78, 86%; and 43/51, 84%, respectively). Inappropriate storage was more commonly reported as a food hygiene fault in homes than in other premises (99/251 (39%) v 343/1309 (26%); χ²=18.2, df=1, P<0.001).

Comment

The downward trend in general outbreaks of infectious intestinal disease linked with the home reflects the national fall in outbreaks of salmonellosis. Foodborne outbreaks in the home seemed to occur when individuals catered for larger groups than usual. However, the surveillance system favours the inclusion of these outbreaks as large outbreaks are more likely to be identified and reported. Our analysis found much evidence that the outbreaks are related to cross contamination in the kitchen and this is supported by experiments that show how easy it is for the environment to be contaminated.4

The downward trend in general outbreaks linked with the home is encouraging and mirrors the national decrease in salmonella infection, which is probably due, at least in part, to the vaccination of poultry flocks. Lowering the risk of introducing salmonella into the home seems to benefit the consumer. Thus, it seems that the food industry can also make a positive contribution to reducing foodborne outbreaks.