In 1961 and 1962 a Working Party of the Public Health Laboratory Service, in which twenty-two laboratories participated, investigated the occurrence of salmonellae in abattoirs, meat factories, butchers' shops and meat products, and their association with human infections.

Thirty-two abattoirs were studied. Salmonellae were isolated from 930 (21%) of 4496 swabs of abattoir drains. There was great variation between different abattoirs, but in general salmonellae were found most frequently in those which slaughtered a high proportion of cattle and a low proportion of sheep; more sero-types were isolated from bacon factories than from abattoirs which slaughtered more than one species of animal. Of 11,347 tissue specimens collected at abattoirs, 218 (1·92%) yielded salmonellae.

Drain swabs from butchers' shops were examined and 73 (6·5%) of 1117 swabs were positive. Meat and meat products were less commonly contaminated but 0·8% of 4127 samples yielded salmonellae.

Salmonella typhimurium was the serotype isolated most frequently from all sources. It was often shown that the same serotypes or phage-types were occurring in abattoirs and in human cases in an area at the same time. In eight food-poisoning incidents, involving a total of 281 cases and excreters, there was convincing evidence that meat or a meat product was the vehicle of infection; in a further twenty-three incidents the organisms causing disease were isolated from sources which suggested that infection might have been meat-borne.

The evidence collected suggests that cattle introduce salmonellae into abattoirs more often than other species of animals. The importance of pigs as a source of human infection is confirmed. Sheep are not a source of salmonella infection in man from meat and meat products, whereas meat from pigs, cattle and calves is a source of infection and is responsible for both sporadic cases and outbreaks of disease.

We wish to thank the many medical officers of health who co-operated in this study. The public health inspectors and abattoir staffs who collected the specimens are too numerous to mention by name, but their invaluable assistance is most gratefully acknowledged. Among the medical officers who assisted us in the survey were: Dr A. Armit (Bridport M.B. and R.D.), Prof. D. B. Bradshaw (Leeds C.B.), Dr C. B. Crane (York C.B.), Dr J. Douglas (Bradford C.B.), Dr A. B. R. Finn (Guildford M.B.), Dr R. A. Good (Winchester M.B.), Dr G. B. Hopkins (Wimborne and Cranborne R.D.), Dr E. W. Kinsey (Caernarvon M.B.), Dr I. B. Lawrence (Dorchester M.B. and R.D.), Dr R. A. Leader (Ipswich C.B.), Dr Mary Lennox (Barry M.B.), Dr V. P. McDonagh (Keighley M.B.), Dr H. E. Nutten (Beccles M.B.), Dr G. O'Donnell (Worcester C.B.), Dr E. J. O'Keeffe (Wareham M.B. and Wareham and Purbeck R.D.), Dr N. F. Pearson (Sturminster Newton R.D.), Dr W. P. Phillips (Cardiff C.B.), Dr T. H. Pierce (Llandudno U.D.), Dr J. L. Rennie (Carlisle C.B.), Dr C. L. Sharp (Bedford M.B.), Dr E. F. Shennan (Evesham U.D.), Dr J. Stevenson-Logan (Southend-on-Sea C.B.), Dr D. W. Wauchob (Blackpool C.B.), Dr J. Walker (Lancashire C.C.), Dr J. V. Walker (Darlington C.B.), Dr R. B. Walker (Kingsbridge R.D.), Dr E. J. Gordon Wallace (Weymouth M.B.), Dr C. Robertson Wilson (Lancashire C.C.), Dr E. M. Wright (Salisbury M.B.), Dr Alfred Yarrow (South East Essex).