-from Epidemiological Bulletin, Vol. 23 No. 1, March 2002-
Rationale for Surveillance
Salmonellosis is one the main causes of foodborne disease. Detection and control
of outbreaks is complicated by the fact that there are over 2,200 serotypes
of Salmonella species, several of which have multiple phage types. Laboratory-based
surveillance of salmonellosis with definitive typing and antibiograms allows
for rapid identification of clusters. Investigations can then concentrate on
individual cases infected with the “epidemic” strain and lead to better identification
of risk factors and implicated food items. Utilization of molecular methods
can lead to even more accurate identification of “epidemic” strains.
Recommended Case Definition
Clinical description
An illness with the following symptoms: diarrhoea, abdominal cramps, fever,
vomiting and malaise.
Laboratory criteria for confirmation
Isolation of Salmonella spp. from the stool or blood of a patient.
Case classification
Suspected: An individual showing one or more of the clinical features.
Confirmed: A suspected case with laboratory confirmation.
Recommended Types of Surveillance
National: The surveillance of salmonellosis is a laboratory-based exercise.
The samples examined by laboratories must be generated from cases presenting
at health centres, hospitals, or in private practice, and practitioners must
be aware of the importance of requesting examination of stool specimens for
public health purposes, especially in cases where food- or water borne transmission
is suspected.
Surveillance is based on a network of laboratories that routinely report data on isolation of Salmonella spp. to central levels. All suspected outbreaks of salmonellosis must be reported to the central level and investigated. In addition, isolates of Salmonella spp. may be sent to a reference laboratory for further typing. Definitive typing data can be analysed on a broad geographical basis; this allows for the detection of outbreaks that may not otherwise be detected.
A minimum data set should be collected on each outbreak at intermediate and central levels. This should be done after the outbreak investigation and include key variables on the nature and extent of the outbreak (time, place, person, possible source).
Note: The laboratory network for surveillance of salmonellosis should be as wide and complete as possible. The concentration of facilities for definitive typing in reference laboratories is useful in order to maintain quality. However, care must be taken when relying on the samples processed in such laboratories as they may not always be representative in terms of clinical spectrum or geography.
International: Reports on notifications, laboratory data and outbreaks to be sent to the WHO Global Database on Foodborne Diseases Incidence as well as to regional surveillance programmes. Reports on investigations of specific outbreaks, particularly those implicating a commercial product, to the WHO Global Database on Foodborne Diseases Outbreaks. ENTER-NET (previously SALM-NET) is an international network where information on laboratory isolations of salmonella and Escherichia coli O157 is shared between countries on much the same basis as within countries. This allows for the detection of outbreaks of international significance and the early warning of countries about contaminated products.
Recommended Minimum Data Elements
Case-based data (from laboratory):
Unique identifier, age, sex, geographical information Date of onset, date of
specimen Specimen type, organism(s) identified.
Aggregated data (from laboratory):
Number of cases by Salmonella species, geographical area and age group.
Outbreak aggregated data:
Specific salmonella identified by species and phage type
Number of people at risk / ill / hospitalized
Number of deaths
Geographical information, outbreak setting (e.g., restaurant, hospital, school)
Date of first and last case
Food or constituent implicated and evidence for implication (e.g., epidemiological
investigation, isolation in food)
Factors contributing to the outbreak (e.g., inadequate storage, inadequate heating,
cross-contamination, infected food handler, environmental factors).
Recommended Data Analyses, Presentation, Reports
Surveillance data
Frequent review of laboratory data for clusters of cases in time, place or person
All suspected clusters must be investigated to establish whether an outbreak
has occurred. Incidence of laboratory identifications by week, geographical
area, organism, age group and sex (map incidence by geographical area if possible).
Outbreak investigation data
Incidence of outbreaks by species, phage type, month, geographical area, setting
of outbreak, attack-rate, duration of outbreak, foods implicated and factors
contributing to the outbreak.
Principal Uses of Data for Decision-making
· Determine the magnitude of the public health problem
· Detect clusters / outbreaks in good time
· Track trends in salmonellosis over time
· Identify high-risk food, high-risk food practices and high-risk populations
for specific pathogens.
· Identify emergence of new species and phage types
· Guide the formation of food policy and monitor the impact of control measures
· Assess risks and set standards
Special Aspects
Human surveillance must be linked with food safety and control authorities.
Source: “WHO Recommended Surveillance Standards, Second edition, October 1999”, WHO/CDS/CSR/ISR/99.2
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Epidemiological Bulletin, Vol. 23 No. 1, March
2002