Why we need a nationwide dengue surveillance system
In 1854, Dr John Snow (not the Game of Thrones character) used a pre-computer method of spatial analysis by mapping patterns and occurrences of cholera outbreaks in Soho, London. He mapped the patients in the neighbourhood and determined that a vast majority of cholera cases occurred around one particular water well.
Last month, when severe dengue outbreak started in Dhaka, I was surprised to note that mapping the dengue patients was something no one had considered. Although it was one of the few first things that should have been done on priority basis. So I voluntarily started to make a map of the patients' location since I had some knowledge about how to make such a map. People voluntarily filled out a google form from where I found the location of the dengue patients which I used to generate the map.
After preparing the map, the first thing I noticed was that dengue patients were mostly concentrated around the hospitals. What this means is that all dengue patients in the hospitals must be kept under mosquito nets and 400 meters radius from the hospital area must go under mosquito and larva cleaning operation.
In January 2019, the World Health Organization (WHO) announced their new 5-year strategic plan, among the 10 highest priority health issues presented, dengue was identified as one of the main infections threatening global health. Intensive action against dengue was proposed by the WHO in 2012 with the aim of reducing dengue mortality by 50 percent and dengue morbidity by 25 percent by the year 2020 (World Health Organization, 2012). The five key elements needed to achieve the dengue public health targets identified by the WHO Global Strategy are diagnosis and case management, integrated surveillance and outbreak preparedness, sustainable vector control, future vaccine implementation, and basic operational and implementation research (World Health Organization, 2012).
Although it was a priority health issue worldwide, we seemed to have downplayed the issue at the beginning. And we have paid the price. In August 2019, the highest number of people were infected with dengue in the last 19 years. According to the IEDCR, a total of 51,734 patients were admitted to the hospitals in August 2019 alone, which exceeded the cumulative number of dengue patients admitted to the hospitals ever recorded. The IEDCR report also shows that nationwide a total of 70,195 patients were admitted to the hospitals from January 2019 till August 31, 2019.
However, all these figures represent the number of patients who were admitted to the hospitals. Patients who had received treatment from outdoors or home were not included in these figures.
Again, the data does not include all the government and private hospitals. For example, the number of dengue patients in Dhaka, shown by IEDCR, were collected from 12 government or autonomous hospitals and 29 private hospitals in Dhaka. But according to Bangladesh private clinic and diagnosis owners Association (BPCDOA), there exist 609 registered private clinics in Dhaka. So, there is a big vacuum of information about the actual number of dengue patients.
Most of us already know by now that all Aedes mosquitos (both Aegypti and Albopictus) do not carry dengue virus. When any female Aedes mosquito bites a Dengue infected person, the mosquito gets infected by the dengue virus. Whenever that infected mosquito bites any person, that person also gets infected. As this cycle continues, the number of infected people rise very quickly.
We have seen that already many actions have been taken to destroy Aedes mosquitos. For example, using mobile phone apps, drones, etc., to locate mosquito's breeding ground are appreciable. These are useful to control mosquitos and can help to run the year-round operations to destroy the breeding grounds.
But we must understand that mosquito control and outbreak control are not the same thing. In order to control an outbreak like that of dengue, the most important thing to do is to identify the patients' location and keep them inside mosquito nets, so that no Aedes mosquitos can further bite the patients and get infected. The second priority is to destroy all the larva and mosquitos within 400 meters radius from the patients' location. 400 meters radius is important because flight range studies suggest that most female Aedes Aegypti may spend their lifetime in or around the houses where they emerge as adults and they usually fly an average of 400 meters (WHO).
One single dengue patient can potentially spread the disease among a hundred more people in a very short period of time, if not counted and not kept under safety net. So, counting every single dengue patient and keeping them under surveillance system is very important. And this surveillance system should be active and be operated in real time data feed. Development and operation of this "Active Surveillance System" is not very easy, but this is the only option we now have.
In Malaysia, Singapore, Queensland-Australia, dengue is a nationally notifiable disease. All dengue cases are required under the Public Health Act to be notified to health departments, where there is a laboratory confirmation of infection by any one of several different methods including virus isolation, nucleic acid testing, detection of dengue non-structural protein 1 (NS1) antigen and dengue virus-specific IgG seroconversion.
We need similar laws. Patients can notify the health department by a toll-free number, website, mobile app with very little information, including location. We can also collect those data from the government and private hospitals and diagnostic centres across the internet. Then by call centre, we can verify every single patient and include them into the main database. Patients' location can be shown on interactive and dynamic maps. Government stakeholders from DGHS, IEDCR, DNCC, DSCC to upazila chairman can see the maps. Anyone can zoom in to any particular location and check the number of dengue patients there—in last 24 hours to last 30 days or even last 6 months. They can take immediate actions to secure the patients and take initiatives to kill the mosquitos and destroy larva in that particular location. Even an automatic notification can be sent to any UNO or chairman of a particular upazila about the number of dengue patients affected in the last 24 hours in their area. But all the relevant stakeholders need to work in coordination for proper implementation of the system.
Our surface temperature is getting warmer due to climate change. And this year we have observed increased rainfall. Both these factors have made the environment suitable for Aedes mosquitoes' breeding. In addition, rapid urbanisation is also creating more suitable breeding condition for these mosquitos.
What is alarming is that this year's dengue outbreak is just the beginning. Next year, it might be even more severe, since dengue patients have already spread across the various districts of the country. Some of these viruses may stay in dormant condition within the eggs until next year. Another worrying part is, these Aedes mosquitos are also carriers of Zika, Yellow fever and Chikungunya. If we do not develop an "Active Surveillance system" and if someone infected with Zika or Yellow fever, comes to Bangladesh, there will also be the risk of Zika or Yellow fever outbreak.
With Bangladesh being one of the most densely populated countries in the world, citizens here are at highest risk of these outbreaks. We may not fully eradicate dengue, but it is possible to keep any of these outbreaks under control by preparing an integrated surveillance and outbreak preparedness system. If we want that surveillance system operational before April 2020, we need to act as fast as we can.
Atik Ahsan is a medical anthropologist and a former Senior Research Investigator of icddr,b.