Health Surveillance and its growing importance in Bangladesh

With the daily dengue hospitalisation cases reaching 1,246 and the total death toll rising to 93 so far this year according to the most recent official data, the importance of having a functional health surveillance system in Bangladesh is again at the forefront of all public health discussions. According to the DGHS data, around 3800 people were undergoing treatment in different hospitals and so far 16,143 people were hospitalised with dengue this year. In 2021 and 2022, dengue cases were 28,429 and 62,382 respectively and the first dengue outbreak was reported in 2000 when 5,551 dengue patients were hospitalised and 93 died in Bangladesh. However, are all dengue cases-- diagnosed, hospitalised, or dengue-related deaths known, captured, and reported?
Health surveillance is the ongoing collection, analysis, interpretation, and dissemination of data on health-related events for use in public health action. Reducing morbidity and mortality in the population and improving population health are the key objectives of public health. Historically, health surveillance was used to monitor infectious diseases but its use has greatly expanded to monitor almost any health-related event, such as chronic disease, injury, health services use or uptake, vector distribution, or occupational and environmental hazards. Surveillance is recognized as the "eyes and ears" of the discipline of public health. To put it simply, surveillance takes a careful look at what is going on in the community.
A good health surveillance system helps in identifying cases for further investigation and research, guiding disease prevention or injury control, setting public health priorities, and evaluating health interventions.
A surveillance system has a few basic elements. First, it is the way of detecting health events and notifying them. This is usually done by a health service provider or a laboratory. Then the information collected and stored in a systematic way is analyzed and interpreted. Finally, this information must reach the right audience so that appropriate and effective actions are taken.
There are a few different types of surveillance. Passive surveillance describes the routine reporting of health data. For example, there are a number of diseases or conditions that are required to be notified by law, and surveillance of these relies mostly on a passive system. The disease registry collects health data. Healthcare providers like hospitals regularly collect data on the number and type of patients that seek treatment.
Passive surveillance is generally inexpensive and can be used to provide baseline data on the health of a population, observe trends or monitor the impact of one or more interventions. These data sets can be linked or aggregated to provide a complete picture of health status. There are a number of limitations of passive surveillance, people having mild or asymptomatic illnesses do not seek medical treatment or there is a lack of access to treatment; these result in underreporting. Laboratory and facilities are needed to diagnose and these may not be enough. Variations in data from passive surveillance systems arise as the social, economic, cultural, and epidemiological factors vary by region or country.
In active surveillance, health data are actively sought out. This surveillance is commonly used during outbreaks. For example, health teams may visit the community to actively seek out cases that may not have otherwise been presented to health centers or hospitals.
Health surveys are a good example of actively seeking out health information; surveys can be done on community members, healthcare facilities, or the entire country. They can be done on an as-needed basis or periodically.
Active surveillance provides more complete and better quality data but is more resource intensive. Another type of surveillance is sentinel surveillance which uses selected institutions or groups to provide health data on specific diseases or conditions. It is useful for monitoring diseases, and trends, and detecting outbreaks. A disadvantage of this surveillance is that it is restricted to a few institutions and cannot detect events that happen outside these. Therefore, it is not that useful for rare or uncommon diseases. Sero-Surveillance, on the other hand, involves testing blood in a selected population for various markers. For example, checking for antibodies can be used to check for active or past diseases.
Another form of surveillance becoming increasingly useful is rumour surveillance; this relies on unofficial sources of information like blogs, internet discussion groups, media gossip, and social media sites. Rumor surveillance can alert health authorities to incidents or events that require further investigation.
Syndrome surveillance involves monitoring nonspecific syndromes like presentations for fever, respiratory or gastrointestinal illness that might highlight illness, like the purchases of certain medicine or higher absenteeism from work or school. This allows early identification of clusters of illness.
The following features make a good surveillance system: 1) it must have clearly stated objectives, 2) it should be easy to operate and straightforward, 3) case definitions are easy to apply, 4) it should be flexible to accommodate changes in information needs or conditions with minimal additional resources, 5) the data should be complete and accurate, and of good quality, 6) data should be accepted by people and organisations participating in surveillance, 7) it should pick up most of the disease that exists in the population, 8) surveillance data should measure what is intended to measure.
The human and material resources involved in running the system must be stable and available as and when needed. Also, surveillance systems need to be evaluated routinely to make sure that they continue to meet their objectives and that they are serving a useful public health function.
Public health experts have already warned of a bigger dengue outbreak in Bangladesh this year unless timely and effective interventions are taken. Therefore, the information gained from a stronger surveillance system must be used for characterising the burden, trends, and patterns of the current dengue outbreak. An integrative approach using all sources of information will provide the best overall picture of the current and future public health crises. The surveillance system must correctly represent the occurrence of a health event in the population with regard to time, place, and person. It must detect health events in a timely manner so that the authorities can take appropriate action.

Hasnat M Alamgir is a Professor and Head of Public Health at the State University of Bangladesh. [email protected]