International epidemiological and microbiological study of outbreak of Salmonella agona infection from a ready to eat savoury snack—I: England and Wales and the United States

BMJ 1996; 313 doi: (Published 02 November 1996) Cite this as: BMJ 1996;313:1105
  1. D Killalea, senior registrara,
  2. L R Ward,
  3. D Roberts, deputy directorb,
  4. J de Louvois, head, Environmental Surveillance Unita,
  5. F Sufi, statisticiand,
  6. J M Stuart, consultant epidemiologista,
  7. P G Wall, consultant epidemiologista,
  8. M Susman, consultant in communicable disease controle,
  9. M Schwieger,
  10. P J Sanderson, consultant microbiologistf,
  11. I S T Fisher, scientific coordinatorg,
  12. P S Mead, medical epidemiologisth,
  13. O N Gill, deputy director (information)a,
  14. C L R Bartlett, directora,
  15. B Rowe, directorc
  1. a Public Health Laboratory Service, Communicable Disease Surveillance Centre, London NW9 5EQ
  2. b Food Hygiene Laboratory
  3. c Laboratory of Enteric Pathogens
  4. d Public Health Laboratory Service, Statistics Unit, London NW9 5EQ
  5. e Barnet District Health Authority, Colindale Hospital, London NW9 5HG
  6. f Wellhouse NHS Trust, Edgware General Hospital, Middlesex HA8 0AD
  7. g European Union Salm-Net Surveillance Network, London NW9 5EQ
  8. h Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, GA 30333, USA
  1. Public Health Laboratory Service, Central Public Health Laboratory, London NW9 5HT. Salmonella Reference Laboratory, Laboratory of Enteric Pathogens L R WU. Leeds District Health Authority, Leeds LS7 3JX M Schweiger, consultant in communicable disease control. Correspondence to: Dr Gill
  • Accepted 9 October 1996


Objectives: To identify the source of an international outbreak of food poisoning due to Salmonella agona phage type 15 and to measure how long the underlying cause persisted.

Design: Case-control study of 16 primary household cases and 32 controls of similar age and dietary habit. Packets of the implicated foodstuff manufactured on a range of days were examined for salmonella. All isolates of the epidemic phage type were further characterised by pulsed field gel electrophoresis.

Results: 27 cases were identified, of which 26 were in children. The case-control study showed a strong association between infection with S agona phage type 15 and consumption of a peanut flavoured ready to eat kosher savoury snack imported from Israel. S agona phage type 15 was isolated from samples of this snack. The combined food sampling results from the United Kingdom, Canada, the United States, and Israel showed that contaminated snacks were manufactured on at least seven separate dates during a four month period between October 1994 and February 1995. Voluntary recalls of the product successfully interrupted transmission.

Conclusions: Rapid international exchanges of information led to the identification of the source of a major outbreak of S agona in Israel and of associated cases in North America. The outbreak showed the value of the Salm-Net surveillance system and its links outside Europe, both for increasing case ascertainment and for improving the information on the duration of the fault at the manufacturing plant.

Key messages

  • International surveillance networks can strength- en infection control

  • When a foodstuff is contaminated it is important to examine as many batches as possible to show the duration of the production fault


  • Funding The Salm-Net surveillance network is a concerted action funded by the European Commission—Directorate General XII, under the Biomedical and Health Research Programme.

  • Conflict of interest None

  • Accepted 9 October 1996
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