Foodborne Outbreak Surveillance and Risk Assessment

An outbreak is an incident in which two or more people, thought to have a common exposure, experience a similar illness or proven infection (at least one of them having been ill).

A general outbreak is an outbreak affecting members of more than one household or residents of an institution.

A food is any substance or product, whether processed, partially processed or unprocessed intended to be, or reasonably expected to be ingested by humans (Reg. (EC) No 178/2002), including drinking water (Reg. (EC) No 178/2002).

Surveillance
Reported data on foodborne disease outbreaks are valuable in establishing a link between foodborne illness and specific foods or situations that caused it. The HPA becomes aware of possible foodborne outbreaks from various sources including the national laboratory reporting scheme, consultants in communicable disease control (CCDCs), Environmental Health Officers (EHOs), microbiologists and the HPA reference laboratories. A structured questionnaire is then sent to the appropriate CCDC with the request that the form be completed by the lead investigator on completion of the outbreak investigation. The questionnaire seeks a minimum set of data on the outbreak, including details of setting, mode of transmission, causative organism and details of epidemiological and laboratory investigations. Data from the questionnaires are stored and analysed.

Statutory Reporting of Foodborne Outbreaks

Information from the surveillance of foodborne disease outbreaks are also provided on an annual basis to the European Food Safety Authority (EFSA) for inclusion in the Community Summary Report on Trends and Sources of Zoonoses, Zoonotic Agents, Antimicrobial Resistance and Foodborne Outbreaks in the European Union. The UK reports data for general outbreaks of foodborne infections. All UK outbreaks reported to EFSA are classified as possible so as not to compromise any prosecutions that might currently be undertaken by regulatory authorities.

Risk Assessment
Risk assessment is a component of risk analysis, which is a formal process used to assess, communicate and manage risk. Risk assessment can be used to evaluate the level of exposure and the subsequent risk to human health from the identified hazard (e.g. foodborne pathogen). Exposure assessment aims to estimate the frequency, and amount of exposure, a human has to the hazard.

Foodborne Outbreaks in England and Wales, 1992-2008

From 1992-2008, there has been a steady decline in the number of foodborne outbreaks in England and Wales (Figure 1). This decline reflects that the proportion of outbreaks attributed to Salmonella, Clostridium perfringens and verocytotoxin-producing Escherichia coli (VTEC) O157 have decreased during the surveillance period.

Figure 1. Total number of foodborne outbreaks in England and Wales from 1992-2008.

Although overall Salmonella continue to be responsible for the majority of foodborne outbreaks reported during 1992-2008 (Figure 2), the proportion of outbreaks caused by particular Salmonella serotypes, such as Salmonella Enteritidis, has decreased during the surveillance period.

Figure 2. Number of foodborne outbreaks attributed to causative organism. Data for England and Wales (1992-2008).

Foodborne Pathogens and Associated Food Vehicles

The Food Standards Agency monitors five key pathogens: Salmonella, Listeria monocytogenes, E. coli O157, Campylobacter and Clostridium perfringens as part of its strategy to reduce foodborne disease.

The Health Protection Agency foodborne outbreak surveillance system captures information on these outbreaks whatever the mode of transmission or causative organism. The various food vehicles implicated in foodborne outbreaks of infection reported in England and Wales during 1992-2008 are detailed in Tables 1 and 2.

It should be noted that in a single outbreak, more than one food vehicle may be associated with infection.

There are some outbreaks where food vehicles were not identified, therefore the total amount of outbreaks associated with the known food categories (n=1791) does not equal the total number of foodborne outbreaks recorded (n= 2365).

Table 1. Foodborne general outbreaks of infection caused by the five key pathogens in England and Wales in relation to implicated food vehicles (1992-2008).

	*Salmonella*	*C.perfringens*	*Campylobacter*	E.coli O157	*L.monocytogenes*
Poultry	191	69	30	3	-
Red Meat	100	117	4	17	-
Fish/Shellfish	41	2	1	-	-
Salad / Fruit / Vegetables	46	9	6	3	-
Sauces	35	9	2	-	-
Desserts	186	3	-	1	-
Milk / Milk Products	21	-	8	13	-
Water	-	-	-	1	-
Miscellaneous	183	19	13	7	2
Eggs	114	-	-	-	-
Rice	12	4	-	-	-
Total	929	232	64	45	2

Table 2. Foodborne general outbreaks of infection caused by other foodbonre pathogens/toxins in England and Wales in relation to implicated food vehicle (1992-2008).

	Other/ Mixed/ Unknown^	Viruses	Bacillus spp.	Scombrotoxin	*S.aureus*
Poultry	19	12	14	-	13
Red Meat	24	7	9	-	11
Fish/Shellfish	78	41	3	61	1
Salad/Fruit/Vegetables	36	16	5	-	1
Sauces	3	2	1	-	1
Desserts	8	7	2	-	-
Milk/Milk Products	4	2	-	-	-
Water	1	-	-	-	-
Miscellaneous	35	32	19	4	8
Eggs	1	-	-	-	1
Rice	6	-	28	-	3
Total	215	119	81	65	39

^Other pathogens include for example Shigella, Cryptosporidium or other toxins. Outbreaks of unknown aetiology included those where no pathogen or toxin was identified.

Recent publications from the scheme:

Little CL, Gillespie IA. Prepared salads and public health. J. Appl. Microbiol. 2008 Dec; 205(6): 1729-43.

Hughes, C., Gillespie, I. A., O'Brien, S. J., & The Breakdowns in Food Safety Group 2007, "Foodborne transmission of infectious intestinal disease in England and Wales, 1992-2003", Food Control, vol. 18, pp. 766-722.

Gillespie IA, O'Brien SJ, Adak GK, Ward LR, and Smith HR. Foodborne general outbreaks of Salmonella Enteritidis phage type 4 infection, England and Wales, 1992-2002: where are the risks? Epidemiol Infect 2005; 133:795-801.

Adak, G. K., Meakins, S. M., Yip, H., Lopman, B. A., & O'Brien, S. J. 2005, "Disease risks from foods, England and Wales, 1996-2000", Emerg.Infect.Dis., vol. 11, no. 3, pp. 365-372.

Gillespie IA, Adak GK, O'Brien SJ, Bolton FJ. Milkborne general outbreaks of infectious intestinal disease, England and Wales, 1992-2000. Epidemiol Infect. 2003 Jun;130(3):461-8.

Lopman BA, Adak GK, Reacher MH, Brown DW. Two epidemiologic patterns of norovirus outbreaks: surveillance in England and wales, 1992-2000.
Emerg Infect Dis. 2003 Jan;9(1):71-7

Meakins SM, Adak GK, Lopman BA, O'Brien SJ. General outbreaks of infectious intestinal disease (IID) in hospitals, England and Wales, 1992-2000.
J Hosp Infect. 2003 Jan;53(1):1-5

Adak GK, Long SM, O'Brien SJ. Trends in indigenous foodborne disease and deaths, England and Wales: 1992 to 2000.
Gut. 2002 Dec;51(6):832-41

Long S, Adak GK, O'Brien SJ, Gillespie IA. General outbreaks of Infectious Intestinal Disease linked with salad vegetables and fruit, England & Wales, 1992-2000.
Commun Dis Public Health 2002; 5(2): 101-5

Frost JF, Gillespie IA, O'Brien SJ. Public health implications of campylobacter outbreaks in England and Wales, 1995-1999: epidemiological and microbiological investigations. Epidemiol Infect 2002;128:111-8

O'Brien SJ, Elson R, Gillespie IA, Adak GK, Cowden JM. Surveillance of foodborne outbreaks of infectious intestinal disease in England and Wales 1992-1999: contributing to evidence-based food policy?
Public Health 2002; 116: 75-80