Effective communicable disease control relies on effective disease surveillance. A functional national communicable diseases surveillance system is essential for action on priority communicable diseases. It is a key part of public health decision-making in all countries (e.g. priority setting, planning, resource mobilization and allocation, prediction and early detection of epidemics, and monitoring and evaluation of disease prevention and control programmes).
There is an urgent need to build on current efforts to strengthen communicable disease surveillance at national level. Strong national systems will form the basis of an effective regional and global network for the surveillance and control of communicable diseases. The development and strengthening of national surveillance requires a substantial and long-term commitment of human and material resources, usually beginning with a systematic assessment of national surveillance activities. This should eventually lead to a national plan for the surveillance of communicable diseases.
What is the "national communicable disease surveillance system"?
Many countries have developed surveillance activities for communicable diseases in order to monitor diseases with a high burden, detect outbreaks of epidemic-prone disease and monitor progress towards national or international control/eradication targets. In this sense, surveillance of communicable diseases is a national function; and the sum of all surveillance activities represents the "national communicable disease surveillance system". The various activities may be integrated into the broader Health Information System (HIS) or may be carried out independently. Surveillance activities have developed in an uneven way. Many activities are managed by different vertical diseases control programmes. In other cases the surveillance function is far removed from the control efforts: data are collected by central statistics offices on a large number of health events, many of which do not represent priorities for the country. In some situations, surveillance for particular health events has been developed by academic or research institutes which have very specific information needs.
Establishing surveillance activities within vertical programmes allows the surveillance function to remain close to the control function. On the other hand, the overall surveillance function in a country can become badly disjointed and inefficient with field workers participating in multiple complicated systems, using different surveillance methods, terminology, and reporting forms and schedules. This entails extra costs and training requirements and often leads to work overload and lack of motivation among health workers. In many cases, huge amounts of data may be collected by central bodies with little of no analysis of that data or use of the information that they provide. The surveillance system becomes driven by the need to collect and move data, little attention being given to the use of information by each level of the health service for decision-making.
What is meant by a "multi-disease approach to surveillance"?
A multi-disease approach to communicable disease surveillance involves looking at all surveillance activities in a Member State as a common public service. These activities involve similar functions and very often use the same structures, processes and personnel. Disease surveillance should be based on collecting only the information that is required to achieve the control objectives. The data required may differ from disease to disease. Specialized surveillance systems are important, especially where surveillance is complex and has specific information needs. Eradication and elimination programmes may require a very active surveillance programme aimed at detecting every case. In other situations, information on outcome may be important. For example, the rate of treatment completion and the cure rate are essential indicators in TB surveillance. Other diseases may require more than one source of data for good decision-making. For example, in HIV/AIDS surveillance the proportion of the population positive for HIV must be monitored as well as the number of new cases of AIDS. This requires special HIV seroprevalence surveillance usually done in a few representative sites ("sentinel surveillance"). Despite the variety of information needs, many elements of data collected in surveillance are very similar and the data source is often the same individual or facility.
There may however, be differences in:
• the specific case detection method used (active case detection vs passive)
• the speed at which data need to flow through the system (immediate vs routine)
• the rapidity of response required (immediate investigation of cases or clusters of
• cases vs analysis of data on a regular basis with subsequent adjustments to a control programme)
For the system to function as an "early warning system", reporting, confirmation, decision-making and response must be rapid. On the other hand, for more endemic diseases, the aim may be to carefully consider data collected in order to adjust or target the control programme. The national surveillance system should therefore be able to accommodate both needs, and will require two-speed reporting mechanisms.
All surveillance systems involve similar functions. It is possible to look at the system as a whole and approach development and strengthening in a coordinated way. The challenge is to identify where synergy between systems is possible, and identify opportunities for coordination or integration of activities, while at the same time recognising the special needs of some programmes for supplementary information or alternative methods of surveillance.
The core functions in surveillance of any health event are:
• case detection
• investigation and confirmation
• analysis and interpretation
These functions are made possible by support functions that improve core surveillance functions:
• setting of standards (e.g. case definitions)
• training and supervision
• setting up laboratory support
• setting up communications
• resource management
The level of coordination/integration in the national surveillance system can affect:
• performance of the system
• cost of the system
• sustainability of the system
One of the important components of the national surveillance plan is a list of priority diseases for surveillance. This list, as short as possible, should be established with the close participation of national health authorities. The rational for prioritizing diseases could use the following series of questions. These questions should be addressed not only from the national perspective but also from a regional, and possibly international, viewpoint as diseases may spread rapidly across national boundaries:
• Does the disease result in a high disease impact? (morbidity, disability, mortality)?
• Does it have a significant epidemic potential? (e.g. cholera, meningitis, measles..)
• Is it a specific target of a national, regional or international control programme? (e.g. the 9th Global Programme of Work (9GPW) disease target, disease targeted for surveillance by a WHO Regional Plan, notifiable disease according to WHO International Health Regulations, WHO international or regional control programme)
• Will the information to be collected lead to significant public health action? (e.g. immunization campaign, other specific control measures to be provided by the central level, international reporting).
In addition to specific diseases, specific syndromes (e.g. haemorrhagic fever syndrome) should be considered for surveillance as well as some specific public health issues (e.g. antibiotic sensitivity of some infectious agents). Following, or possibly preceding, the list of priority diseases, an inventory of existing surveillance activities should be carried out. This should be based on thorough site visits and a review of all key components of the health system, including public and private sectors where appropriate, as well as nongovernmental organizations involved in long term health activities in the country. The following elements should be addressed for each disease or syndrome under surveillance:
• is the case definition:
- consistent throughout the surveillance system?
• is the reporting mechanism:
- of appropriate reporting periodicity?
- available to all relevant persons and institutions?
• is the analysis of data:
- susceptible to proper presentation?
- used for decision-making?
• do the personnel involved:
- have a good understanding of the value of the surveillance system?
- understand, show interest in, and support, their own surveillance task?
- have enough appropriate human and material resources?
• do the personnel involved receive appropriate:
• is the feed-back from intermediate and central levels:
When the assessment of current activities is done, the next question is:
• Is there an operational control programme for each of the priority diseases?
Current surveillance activities must be reviewed against what is needed and any gaps identified. Some diseases or syndromes may already be subject to routine surveillance (i.e. the periodic reporting of data on cases of selected diseases) or there may be a requirement to report the disease or syndrome immediately on suspicion or diagnosis. This is especially true for diseases that may lead to epidemics. However, certain diseases may have alternative or supplementary surveillance methods such as laboratory-based or sentinel surveillance. The emphasis should be on a minimum set of data to be collected, analysed and acted upon at each level of the system. Only that information that aids public health decision-making should be collected.
Once priority diseases have been selected and the gaps identified, a plan of action for surveillance should be developed. An integrated approach which aims to coordinate and streamline all surveillance activities is advised. To this end a central body, which may be based in the Ministry of Health, should coordinate all the surveillance activities.
The key decisions in development of surveillance are those relating to case definitions and surveillance methods. Compromises may have to be made on the choice of surveillance method and the minimum data elements in order to ensure an integrated approach. In this document, case definitions are tailored for the purposes of epidemiological surveillance with the inclusion in many cases of "suspected" or "clinical" case definitions. There is some overlap between syndromes and diseases. In some situations a syndromic approach is appropriate whereas in others a disease specific approach is preferable. In fact it is likely that countries may use a syndromic approach at the peripheral levels but a more specific diagnosis should be used in the investigation and confirmation of outbreaks. In all cases, terminology should be clear and agreed upon by all partners in the surveillance activities.
Surveillance priorities should be appropriate to the disease epidemiology, infrastructure and resources in each country. National surveillance systems should reflect global goals for communicable disease control as stated in the WHO 9th Global Programme of Work (9GPW) and be in line with regional surveillance plans defined by WHO Regional Offices. It is essential that feedback loops be built into the system. This may be a regular epidemiological bulletin with tables and graphs showing trends, progress towards targets and reports on the investigation and control of outbreaks. It is crucial that the personnel involved in surveillance activities be trained for their surveillance tasks, and there is also a need for ongoing in-service training at all levels, e.g., through workshops followed by close supervision in the field. This could be best accomplished in close collaboration with WHO'S Regional Offices and possibly, by setting up a national training programme in field epidemiology (e.g. EPIET, FETP).
Fig. 1 shows a case where Leptospirosis is not perceived as a priority and is not subject to surveillance activities. However, bacterial meningitis, which is perceived as a priority disease, is not subject to surveillance activities- and this should be remedied.
Figure 1: Sample Gap Analysis in National Surveillance Assessment