Epidemiological Surveillance

Epidemiological Surveillance

The epidemiological approach consists of describing and measuring the frequency of a health phenomenon, such as a disease, and of distributing it according to the characteristics of the person, place, and time, in order to formulate hypotheses on the determinants of this frequency. These measurements can only be made through epidemiological surveillance, which is an important source of data in epidemiology.

Definition of epidemiological surveillance

Systematic and continuous process of collecting, analyzing and interpreting data on important health events;

For the planning, implementation, and evaluation of public health practices

Objectives and Goals of Epidemiological Surveillance
- Describe

Assess the extent of a health phenomenon and monitor its evolving trends according to the characteristics of time, person, and place.

Alert

Detect acute phenomena (epidemics, emerging pathologies) requiring rapid action.

Assess

Evaluate the impact of prevention and control measures.

Seek

Generate hypotheses about risk factors.

Types of Surveillance 1- Passive Surveillance

The information is transmitted without any prompting or intervention from the monitoring services. The system waits for notifications.

Example: mandatory disease reporting system.

Active surveillance

It is the collection of data periodically through regular contact with the relevant departments to inquire about the presence or absence of new cases of a particular disease. The system searches for the information.

Example: monitoring of nosocomial infections.

Sentinel surveillance Sentinel surveillance by network

A group of services, clinics, medical practices or laboratories that report, at regular intervals, the number of recorded cases of a particular disease, as part of a voluntary commitment.

Sentinel surveillance by site: Special surveillance which is carried out in a limited manner in time and space and which is repeated regularly at the same time of year.

It allows the trend of a specific disease to be monitored, in a specific location and among particular groups of the population.

Example: sero-surveillance surveys carried out by the HIV surveillance sentinel site in Algeria.

Choice of Data Sources
Mandatory Disease Notification Systems

Notifiable diseases (NDDs) are diseases that require mandatory transmission of individual data to the health authority.

This method of surveillance is very old and is universally used.

The monitoring of MDOs at the level of a country or a smaller administrative area is generally governed by specific and regularly updated legislative texts.

In Algeria, decree No. 179 and circular No. 1126 of November 17, 1990 established the list of diseases requiring mandatory notification and the procedures for their notifications.

The World Health Organization (WHO) under the International Health Regulations (IHR) requires that all cases of quarantinable diseases (cholera, plague and yellow fever) reported in a country be notified to the WHO.

Monitoring Systems by Biological and Medical Analysis Laboratories: Very often coupled with the MDO notification system, essential when you want to:

Detect the emergence of new epidemic strains of a microorganism.
Monitor for the development of possible chemoresistance.

Hospital Monitoring Systems

Hospitals are an important data source for MDO reporting.

A special case of hospital surveillance is represented by the surveillance of nosocomial infections.

Epidemiological Surveillance Sentinel Networks

Some health problems can only be monitored through general or specialist private practitioners, e.g.

Contagious childhood diseases (mumps, rubella, measles, chickenpox, etc.)
Flu syndromes,
Certain sexually transmitted diseases.

Epidemiological Surveillance and Feedback

Without regular communication of results from the central level to the periphery, any monitoring system will quickly become exhausted.

In the feedback on diseases or any epidemic process, at least the following elements must be specified:

The number and temporal-spatial distribution of cases and deaths.
The results of laboratory tests.
Sources of infection.
Populations at risk.
Measures for preventing and controlling the epidemic process in the event of an epidemic. The formatting of the results for feedback should be attractive, particularly by alternating tables, graphs, and comments.

Examples:

Monthly Epidemiological Survey (MES) of the INSP in Algeria.
WHO Weekly Epidemiological Record (WER).
Morbidity and Mortality Weekly Report (MMWR) published by the CDC in the USA.
Weekly Epidemiological Bulletin (BEH) in France.
Health Laboratory Service (PHLS) Communicable Disease Report in the United Kingdom.

Description of a Surveillance System
- Specify the objectives initially set
- Represent the different levels of the system and the functional links that unite them in the form of an organizational chart
- Specify the case definition used, the sources of information , the observation period , the target population for surveillance, the methods of data transmission and statistical analysis
- It is important to know whether the monitoring is active or passive and whether it is comprehensive or not.
Usefulness of a Surveillance System

Detect trends or episodes.
Assess the significance of the health problem.
Develop research programs.
Identify risk factors.
Measure the effectiveness of preventive measures.
Improving the practice of healthcare providers.

Cost of a Surveillance System
- Direct costs: salary costs, travel expenses and other operating costs (mail, telephone, IT, etc.).
- Indirect costs: costs of laboratory tests necessary to confirm the diagnosis, and costs imposed by the treatment of reported cases and contact subjects.

Weigh this estimate of expenditure against the quantified benefits that we hope to gain from monitoring.

Quality Criteria of a Surveillance System

Usefulness: This essentially involves assessing whether the system is well suited to the objectives set.

Simplicity: Easy to understand and apply, lightweight structure, rapid and standardized information collection and transmission procedures , it is inexpensive

Flexibility: This is the ability of the system to easily adapt to changes in the case definition, the data to be collected or the sources of information.

Acceptability: This is the level of adherence of the individuals and organizations participating in the surveillance system. This quality is affected by the complexity of the procedures and media used, as well as by the amount and type of data to be collected.

Sensitivity: This is the ability to detect a phenomenon when it actually exists. The system must be able to identify all cases.

Specificity: The specificity of a surveillance system is much more difficult to measure than its sensitivity. It is its ability to report few false positives.

Representativeness: it is the capacity of a system to correctly describe the distribution of health phenomena according to the characteristics of time, place and person.

Reactivity: this is represented by the speed of circulation of information, detection of epidemic episodes and the establishment of control measures.

This is the time between the appearance of the monitored phenomenon and the intervention.

Scope of Application of Epidemiological Surveillance
- Infectious diseases.
- Vaccine-related infections.
- Healthcare-associated infections.
- Antibiotic use and link with bacterial resistance.
- Adverse events associated with healthcare and health products.
- Health and environment.
- Chronic diseases.
- Traumas.
- Health monitoring and bioterrorism.

– …

Epidemiological Surveillance in Algeria
Organization of the Health System in Algeria The period 1962-1972

Implementation of care and prevention measures for prevalent communicable diseases (diphtheria, tetanus, whooping cough, poliomyelitis, measles, tuberculosis, typhoid, typhus, cerebrospinal meningitis, malaria, etc.).

The period 1973-1986

The introduction of free healthcare in 1973,
Implementation of the expanded vaccination program (EPI) in 1975,
The establishment of the communicable disease surveillance system in 1986.

The period 1987-2003

Establishment of Order No. 179 of November 17, 1990 establishing the list of MDOs and the procedures for their notifications.
Establishment of Circular No. 1126 of November 17, 1990 relating to the communicable disease surveillance system.

The period from 2004 to 2011

Executive decree 07-140 of May 19, 2007 transformed the 185 SS into 189 public hospital establishments (EPH) and 273 public local health establishments (EPSP).
Adoption by the Ministry of Health of a national plan to combat cancer in 2011.

Epidemiological Surveillance of MDOs

Among the essential elements of epidemiological surveillance, the mandatory reporting of certain diseases remains the oldest and best known to practitioners.
In Algeria, decree No. 179 and circular No. 1126 of November 17, 1990 established the list of MDOs and the procedures for their notifications.
Circular No. 1126 of November 17, 1990 relating to the communicable disease surveillance system.
All doctors, pharmacists and laboratory managers, regardless of their location or practice regime, are required to report suspected or confirmed MDOs.
After an epidemiological investigation and the implementation of prophylactic or control measures if necessary, this service establishes a weekly report on disease declarations.
This statement is regularly sent in one copy to the Directorate of Health and Population of the Wilaya.

Example 1 : Morbidity Registers (e.g. Cancer Registers)

In Algeria, the establishment of cancer registries in different regions of the country was done towards the end of 1980: e.g.

Digestive cancer registry for the wilaya of Algiers: 1985 extended to all locations from 1992.
Cancer registry of the wilaya of Sétif: 1989.
Cancer Registry of the Wilaya of Oran: 1994.

Objectives of the Cancer Registry

Determine the incidence and temporal trends in overall and specific incidence.

Example 2 : Network Surveillance

Surveillance of Influenza Syndromes

The seasonal flu surveillance sentinel network called the Regional Flu Observation Group (GROG) covers 9 wilayas: Algiers, Blida, Boumerdes, Tipaza, Tizi Ouzou, Médéa, Constantine, Sétif, and Guelma.

The objectives of the network are:

Monitor flu-like symptoms weekly to detect an epidemic situation early.
To determine the person, time and place characteristics of influenza syndromes diagnosed by sentinel physicians, including age, population at risk, etc.

Identify circulating strains in order to implement appropriate health actions and study the distribution of isolated viruses according to type, subtype and epidemiological characteristics.
Participate in the WHO global influenza surveillance network for the selection of vaccine composition for the following season.

Example : monitoring of bacterial resistance to antibiotics

Network Activities:

Quality control of the antibiogram.
Organization of seminars and workshops.
Resistance monitoring.
Health monitoring: alerts.
Study of antibiotic consumption.
Fight against self-medication and inappropriate use of antibiotics.

Example 4 : HIV Surveillance

Sero-surveillance surveys are carried out periodically

XIII. Conclusion

Epidemiological surveillance is an essential system for disease control . It detects abnormal phenomena early and enables preventive actions and effective disease control.

The evaluation of a monitoring system must allow:

To judge whether the objectives set during its implementation have been achieved.
To issue recommendations for its improvement.