4.2 Epidemiological surveillance

Epidemiological surveillance permits early detection of new outbreaks.  

Community-based surveillance can add useful information to the data from health care facilities.

An early warning system can help the teams prioritise their actions to target areas likely to be having an outbreak, decide whether an investigation is warranted, and prepare for a more rapid field investigation.

The alert notion is subjective. Defining alert criteria involves finding a compromise between criteria that are highly sensitive (allow very early detection of increasing cases but may trigger unnecessary actions) and ones that are not very sensitive (detect increasing cases later but trigger fewer unnecessary investigations).

If the geographic area to be covered is large, consider a targeted approach that focuses resources on the areas at highest risk of a large outbreak. These areas can be identified based on immunisation coverage estimates (survey-based estimates are more reliable than administrative coverage estimates) or more complex mathematical methods [1]Citation 1.Cutts FT, Dansereau E, Ferrari MJ, et al. Using models to shape measles control and elimination strategies in low- and middle-income countries: A review of recent applications. Vaccine. 2020;38(5):979-992. doi:10.1016/j.vaccine.2019.11.020 . The targeted approach can include more sensitive alert thresholds, more robust surveillance efforts, and prioritising those geographic areas for investigation/intervention in case of alert.  

Once an outbreak has been confirmed, epidemiological surveillance must be stepped up. 
The goals of the surveillance system are:

• To monitor how the outbreak is evolving
• To provide indications for organising an appropriate response (care and vaccination)
• To evaluate response activities

4.2.1 Case registration

The registers (Appendix 5) are the foundation of all data collection. The decision is whether to set up special registers for measles cases or to use the existing registers. Whichever approach is chosen, registers must be available in every facility and must remain there.

Line lists allow detailed, centralised information and make it easier to analyse. The following information should be collected for each measles case:  name, address, sex, age, vaccination status, date of symptom onset, admission date, progress, and laboratory diagnosis.

4.2.2 Description of the epidemiological surveillance system

Data

Basic information
At the end of every epidemiological week, all health care facilities send their weekly measles data up to the next higher level.
 

Zero reporting
If there were no cases seen over the course of the week, this information should be transmitted. This is known as “zero reporting”. Failing to report is equivalent to missing data and does not mean there were no cases.

Data transmission

Use the fastest means of communication available to transmit data (telephone, SMS, MMS, email, radio, etc.). If necessary, equipment can be provided to facilitate transmission.

If transmitting the data verbally, a paper copy of the report should always be sent up to the next level and another kept at the facility.

Every visit to a health care facility in an affected region (supervision of treatment activities, supply or vaccination) is an opportunity to supervise and facilitate data collection and transmission.

Data compilation

Data are usually compiled and analysed at the district level (incidence rate, attack rate and case fatality rate) and then transmitted to the regional level. After compilation and analysis at the regional level, the data are transmitted to the national level.

At each level, the person responsible for surveillance checks the data for completeness and their timely transmission. They enter them, verify concordance and link them to the laboratory data, if applicable.

Data analysis

The analysis (Time - Place - Person) is done at every level, every week, as soon as the epidemic season begins. This is a crucial step for identifying and managing outbreaks.

Displaying the data in the form of tables, graphs (Appendix 6) and maps facilitates the analysis. A computer software tool makes it easier to organise the data. If not available, e.g. in a dispensary, trends (cases and deaths) can be monitored by posting a simple graph on the wall and updating it weekly.

Laboratory surveillance

After the first few samples (confirmation and genotyping), it is not necessary to monitor continually throughout the outbreak, though it might be useful, as the outbreak is ending, for confirming that measles is still the issue. For laboratory surveillance, consult the country’s national recommendations.