Epidemiological Surveillance Systems and Data Analysis

Epidemiological Surveillance

A set of activities and procedures on sickness, death and syndromes under surveillance and compulsory notification, generating information on their behaviour and trends to support timely interventions and to achieve immediate control of such events.

Passive Surveillance

Passive surveillance is the routine system of reporting events, including the system of notifiable diseases.

It is often the simplest system to implement but can be complex to organize and maintain.

However, its main limitations are low specificity and limited representativeness; it depends on notification coverage, and reporting can be affected by trends that increase or decrease the number of reported cases.

Active Surveillance

Active surveillance is conducted when health-service officials contact patients directly to determine whether cases have occurred and to collect the necessary information.

These systems are more expensive than passive surveillance, but the data are generally more specific, more complete, and more valid.

They can be used for short periods and for research purposes.

Sentinel Surveillance

Sentinel surveillance uses information derived from a selected group of reporting sources within the health-care system (sentinel units) to monitor an event of interest.

It focuses on key events that provide early warnings; sentinel sites detect and report these events.

Sentinel surveillance is often applied to events that require specialized laboratory diagnosis.

Diagnostic Monitoring Forms

Some of the functions of diagnostic laboratory monitoring are:

• Confirmation of acute infection
• Molecular characterization of the infectious agent
• Confirmation and identification of the source of infection
• Identifying sources of transmission
• Measurement of population immunity
• Measurement of the effectiveness of control strategies
• Analysis of severe or unusual clinical cases

Data Analysis

Time, Place, Person

Time

Place

An important element in data analysis is identifying where cases occur within the population's geographic space.

For this, we use geographic information systems (GIS) and software that create a graphical description of events under surveillance to identify clusters or outbreaks.

Person

The person variable allows us to identify groups at risk. Common characteristics considered include:

• Age
• Race
• Sex
• Marital status
• Immunity
• Nutritional status
• Education
• Lifestyle and risk factors
• Other relevant characteristics