Explanatory notes

This document attempts to identify the key activities and tasks associated with the surveillance of a range of communicable diseases. To avoid confusion, administrative level names (e.g. "district", "province") are not used. Instead, an attempt has been made to break down the surveillance activities into functional levels, concentrating on the various activities that would usually be carried out at each level (i.e. peripheral, intermediate, central). It is important to note that this represents only a prototype that would have to be adapted to reflect the structure and level of sophistication of existing health services. No matter what structure is decided upon, each level must have adequate resources and receive appropriate training.

Figure 2: Schema for information flow in Communicable Disease Surveillance

The peripheral level: first point of contact of an ill person with the health services. The patient is usually seen by a primary care physician, clinical officer or nurse. It is normally at this level that the first opportunity for epidemiological surveillance occurs. However, it must be remembered that surveillance is only one of many tasks. The staff at this level are unlikely to have epidemiological training and may in fact see the recording and reporting of information on cases as administrative and unimportant. The situation is made worse by case definitions that are confusing and difficult to apply and by having an excessive number of reportable diseases. In order to be successful, the collection of information must be simple and useful locally. To this end a limited number of easily recognizable diseases or syndromes should be decided upon. These should not normally involve extensive confirmatory procedures (unless these procedures are essential) and the principle should be the reporting to intermediate level of suspected rather than confirmed disease. The method of recording should be in harmony with clinical record keeping practices and not duplicate them. It is desirable that the personnel have the opportunity and the ability to chart and tabulate their own data in order to monitor local trends. In addition the immediate reporting of a disease with epidemic potential should be followed by an equally immediate response.

Tasks at the peripheral level:

· diagnosis and case management
· reporting of cases
· simple tabulation and graphing of data

Certain conditions may be subject to community-based surveillance. Community-based surveillance in this context means the detection and reporting of diseases from within the community usually by local people or leaders who have received basic instruction on how to recognize certain conditions. The decision to base surveillance in the community must be based on a clearly identified needs and advantages over health care unit-based surveillance. The role of nongovernmental organizations (NGOs) working in the field, including missions' health facilities, as well as the role of the private sector, have become increasingly important in disease surveillance. These partners must be considered in the national surveillance plan where possible.

The intermediate level, at which data are collected from the peripheral level. Its main function from the perspective of communicable disease surveillance and control is ongoing analysis of data from the periphery in order to recognize outbreaks or changes in disease trends. These analyses must be associated with responses such as investigation and intervention. Effectiveness of interventions can be monitored using the same data sources.

Countries may have two intermediate levels (e.g. district and region). This will depend on the size of the country and the structure and level of development of the health service. In many cases the professional at this level will have other tasks in the area of programme management. The tasks must be manageable and the surveillance data be perceived as immediately useful. In some cases it may be more appropriate that the task of outbreak investigation be undertaken from the central level.

Tasks at the intermediate level:

· case management which can not be done at the peripheral level
· analysis of data from the peripheral level for:

- epidemiological links
- trends
- achievement of control targets

· provision of supportive laboratory data (or laboratory diagnosis if possible)
· investigation of suspected outbreaks
· feedback of information to the peripheral level
· reporting of data and suspected/confirmed outbreaks to central level

The central level is usually at the national level where policies on infectious disease are set and where resource allocation most often occurs. The central level in some large countries may actually be at a federal level. The central level plays a key role in supporting the intermediate levels, by providing services that are not available elsewhere, such as high level epidemiological skills or laboratory facilities. The central level must also be able to deal with outbreaks of national importance in a coordinated fashion. In addition, overall disease trends can be analysed and resources for disease control targeted to high-risk areas. The central level must liaise with other countries and international agencies in the response to outbreaks of international significance and in the management of diseases subject to the International Health Regulations, or to agreed targets for control or elimination. The central level may have access to alternative data sources such as national reference laboratories where the identification of unusual organisms should trigger a response.

Tasks at the central level:

· overall support to, and coordination of, national surveillance activities

· provision of laboratory diagnosis data if not available at intermediate level (use regional or international reference laboratories if required)

· analysis of data from intermediate level for:

- epidemiological links
- trends
- achievement of control targets

· support to intermediate level for outbreak control

- case management
- laboratory
- epidemiology
- education
- logistics

· feedback to intermediate level, and possibly to the peripheral level

· report to WHO, as required (International Health Regulations, specific needs of control programmes)

Collaboration with non-medical sectors such as agriculture, veterinary medicine, and environment must be considered where appropriate (e.g. water or foodborne diseases, vector-borne diseases, human zoonoses).

Zero Reporting: Whatever the structure of the surveillance system, data on priority diseases or syndromes should move smoothly through the system triggering the appropriate responses throughout. The system should include zero reporting: each site should report for each reporting period even if that means reporting zero cases. This avoids the confusion of equating "no report" with "no cases". In addition the surveillance system must include performance indicators for reporting (e.g. completeness and timeliness of reports).

Feedback: It is essential that feedback loops be built into the system. This may be through regular epidemiological bulletins with tables and graphs showing trends and progress towards targets and reports on the investigation and control of outbreaks.

Sample Format		Cholera
A00		Cholera
RATIONALE FOR SURVEILLANCE
Cholera causes an estimated 120 000 deaths per year and is prevalent in 80 countries. The world is currently experiencing the 7th pandemic. In Africa epidemics have become more frequent and case-fatality rates are high. Refugee or displaced populations are at major risk of epidemics due to the conditions prevailing in the camps (unsafe water, poor sanitation and hygiene). Control of the disease requires appropriate surveillance with universal case reporting. Health education of the population at risk and improvement of living conditions are essential preventive measures. Case reporting universally required by International Health Regulations.				ICD code Disease name Rationale for surveillance
RECOMMENDED CASE DEFINITION
Clinical case definition
	· In an area where the disease is not known to be present, severe dehydration or death in a patient aged 5 years or more or
	· In an area where there is a cholera epidemic, acute watery diarrhoea with or without vomiting, in a patient aged 5 years or more*			Recommended case definition
Laboratory criteria for diagnosis
Isolation of Vibrio cholerae O1 or O139 from stools in any patient with diarrhoea
Case classification
Suspected: A case that meets the clinical case definition
Probable: Not applicable
Confirmed: A suspected case that is laboratory-confirmed
Note: in a cholera-threatened area, when the number of "confirmed" cases rises, shift should be made to using primarily the "suspected case" classification,
*Cholera does appear in children under 5 years; however, the inclusion of all cases of acute watery diarrhoea in the 2-4 year age group in the reporting of cholera greatly reduces the specificity of reporting. For management of cases of acute watery diarrhoea in an area where there is a cholera epidemic, cholera should be suspected in all patients.
RECOMMENDED TYPES OF SURVEILLANCE
Routine surveillance (This may be integrated with surveillance of diarrhoeal diseases, see acute watery diarrhoea).
Immediate case-based reporting of suspected cases from periphery to intermediate level and central level. All suspected cases and dusters should be investigated.				Recommended types of surveillance
Aggregated data on cases should also be included in routine weekly/monthly reports from peripheral to intermediate and central level.
International: Initial suspected cases should be reported to WHO (mandatory)
	Aggregated data on cases should be reported to WHO (mandatory)
Outbreak situations:
	· During outbreak situation surveillance should be intensified with the introduction of active case finding
	· Laboratory confirmation should be performed as soon as possible
Thereafter weekly reports of cases, ages, deaths, regions, and hospital admissions to be set up
RECOMMENDED MINIMUM DATA ELEMENTS
Case-based data for Investigation and reporting				Recommended
Age, sex, geographical information				minimum
Hospitalization (Y/N)				data elements
Outcome
Aggregated data for reporting
Number of cases by age, sex
Number of deaths
RECOMMENDED DATA ANALYSES, PRESENTATION, REPORTS				Recommended data
Use weekly numbers, not moving averages				analyses,
Case-fatality rates (graphs)				presentation, reports
Weekly/monthly plots by geographical area (district) and age group (GIS) (graphs)
Comparisons with same period in previous five years
PRINCIPAL USES OF DATA FOR DECISION-MAKING				Principal uses
Detect outbreak, estimate the incidence and case-fatality rate				of data for
Undertake appropriately timed investigations				decision-making
Assess the spread and progress of the disease
Plan for treatment supplies prevention and control measures
Determine the effectiveness of control measures
SPECIAL ASPECTS
At least one reference laboratory in each country is recommended for species identification.
Once the presence of cholera in an area has been confirmed, it becomes unnecessary to confirm all subsequent cases.; shift should be made to using primarily the "suspected" case classification
Monitoring an epidemic should, however. include laboratory confirmation of a small proportion of cases on a continuing basis				Special aspects
For countries where cholera is rare or previously unrecognized, the first cases should be confirmed by laboratory diagnosis (including demonstration of toxigenic Vibrio cholerae O1 or O139 in faeces if possible).
CONTACT INFORMATION
Regional offices
See Regional Communicable Disease contacts on pages 18-23				Contact information
Headquarters, 20 Avenue Appia, CH-1211 Geneva 27,
Communicable Diseases Surveillance and Response (CSR) Switzerland
E-mail: tikhomirov@who.ch / outbreak@who.ch
Tel: (41 22) 791 2688 / 2662 12111			Fax: (41 22) 791 4893 / 0746 attn CSR