Disease Surveillance

Definitions and Concept of Surveillance

Disease surveillance is the ongoing systematic collection, consolation and analysis of data, and the dissemination of this information to those who need to know, so that actions may be taken. Surveillance is undertaken to inform disease prevention and control measures. Surveillance helps managers determinewhether immunization activities are achieving their objectives and goals or not.

The success of any immunization program is indicated by reduction of incidence and ultimately, disappearance of the target disease from the community, which is detected by the surveillance. Surveillance dose not have to be complex. In fact, a common problem with many surveillance systems is that they are too complex. So much time is spent collecting data that little time is left for taking actions that will reduce the number of cases of disease. For this reason, it is important to collect onlyas much data are needed and will be used.

It is very important that more actions should be taken at the level at which the data are obtained. This is especially true for district and peripheral health centers, where most of the health services are provided. If the managers at this level wait to take any action until feedback comes from the center, it may be too late.

Types of Surveillance

1. Routine surveillance

In routine surveillance, the data are collected routinely and forwarded to higher levels on a routine basis. For this purpose, health staff of sub health post, health post and health center collect information about the number of the cases of reportable communicable diseases including the EPI target diseases that occur in their health area. health staff may also investigate each case of neonatal tetanus and polio. At the end of the month they analyze the data and send it to the district supervisor.

2. Sentinel surveillance

It occurs when data are collected from only selected sites. this is rarely representative of thepopulation but can be used to monitor trends and collect more detailed information.

Sentinel sites are chosen to report the number of cases of disease that occur for specific time period and also in certain age group. They may also provide a more consistent picture illness in a givenarea. Data collected from these sites may also show whether the routine reporting data is working. In Nepal. Early Warning Reporting and Response System has been developed for national priority diseases and different sentinel sites has been identified for the data collection.

3. Case/outbreak investigation

In general, case investigation is an investigation of single case and an outbreak is that of many cases. However, when the occurrence of a particular disease is very low, even one case can be considered an outbreak.

The supervisor of concerned health facilities should investigate every case of neonatal tetanus and polio as soon as the case is suspected. Case incestigationof the other EPI target diseases, and other diseases of public health concern should be done when appropriate. The role of district supervisors in most outbreak investigations is to analyze the surveillance data and to notify higher officials of any disease trends that might indicate occurrence of outbreak.

4. Special studies

These studies conducted by trained health professionals, investigators or epidemiologists. They are used to measure the number of cases of disease in area and to evaluate the reliability of the routine or sentinel reporting.

Purpose of Surveillance

The surveillance is done for the following purposes:

• Observe disease trends and identify the disease as per case definition and causes
• Establish disease priority
• Identify, investigate and control outbreaks
• Identify, investigate and manage adverse events following immunization
• Document impact off services
• Estimate the requirement of vaccine/drugs and other logistics
• Evaluate quality of health service delivery
• Identify specific population groups at high risk of illness and deaths due to vaccine preventable diseases (VPDs) and other health problems
• Ensure that national immunization program (NIP) activities and resources are used efifciently
• Modify strategies for betterment

Importance of Surveillance

1. Highlighting the magnitude of the illness as a public health problem

• Large number of children or women affected
• High mortality rates
• Causes of lifelong debilitating sequelae
• Assessing impact of services which includes achieving goals of polio eradication, neonatal tetanus elimination, and control of measles as well as other VPDs like diphtheria, pertussis and childhood tuberculosis
• Assessing if unequal weight age and importance is given to either of the components of National Immunization Program (NIP) and to take corrective measures in time.

2.Providing epidemiological data for planning program interventions

• Which are the age groups most affected?
• WhichWhich locations/ geographical areas are more affected?
• Are there seasonal variations?
• Are there cyclic trends?
• Are some groups of the community more vulnerable?
• Are there factors that affect complications and mortality rates?

3. Monitoring the quality of services

• Is the program having the expected impact on the incidence and mortality rate?
• Do the trends commensurate with services provided?
• Immunization status of cases
• Is the quality of the work has been assured by the program?

4. Identifying high risk pockets for additional actions

• Is the program having less than desired impact in some pockets?
• Are the reported incidence and mortality rates higher in selected pockets?
• Is the reported incidence of severe adverse events higher in selected pockets?

5. Identifying outbreaks early

• Prevent deaths by early and appropriate case management
• Prevent secondary cases
• Help in planning proper interventions
• Prevent spread of the outbreak to the other vulnerable pockets
• Early and appropriate treatment to prevent deaths

6. Estimating the requirement of vaccines for the programs

The surveillance data enable to judge the magnitude of the problem to identify the population to be covered and to determine the requirement of vaccine and other logistics in certain geographical area.

7. Documenting impact of services to show

• Declining trends of diseases
• Reduction in neonatal, infant and child mortality rates.

References

Gordis, L. Epidemiology. third edition. 2004.

Joshi, Banjara. Fundamentals of Epidemiology. Kathmandu: Quality Printing Press, 2007

Park, K. Park's Text Book of social and prevention Medicine. 18th edition. 2008.