Outbreak at a glance 

As of 20 November 2022, a total of 52 807 laboratory-confirmed dengue cases and 230 related deaths have been reported by the Ministry of Health & Family Welfare of Bangladesh since 1 January 2022 with a case fatality rate (CFR) of 0.44%. Dengue is endemic in Bangladesh however a surge of cases started in June 2022. Currently, all eight divisions in the country are reporting cases and deaths. This is the second-largest outbreak since 2000, with the largest having occurred in 2019. The current dengue outbreak is unusual in its scale and seasonality.

Description of the outbreak

Between 1 January and 20 November 2022, a total of 52 807 dengue cases including 230 related deaths (case fatality rate = 0.44%) were reported by the Ministry of Health & Family Welfare (MOHFW) (Figure 1). The cases were confirmed either by non-structural protein (NS1) diagnostic kits or by Immunoglobulin M (IgM) tests. According to information available for 40% of reported cases (n=20 982) the median age is 25 years (range: 0 – 89) with males accounting for 60% of the cases. This is the second highest annual number of cases since 2000, the highest having occurred in 2019, when 101 354 cases including 164 deaths were reported (Figure 2 & 3).

The most affected division is Dhaka, accounting for 70.6% of cases and 60.4% of deaths. Dhaka city, the largest city in Bangladesh, located in Dhaka division, has reported 64.5% (n= 34 071) of the total number of cases. Other affected divisions include Chattogram division (13.2% of cases and 24.8% of deaths) and Khulna division (5.5% of cases and 4.8% of deaths) (Figure 4).

The high incidence of dengue cases this year is taking place in the context of an unusual amount of rainfall since June 2022, accompanied by high temperatures and high humidity which have resulted in an increased mosquito population throughout Bangladesh.

Figure 1.   Number of dengue cases and deaths reported in Bangladesh from 1 January to 20 November 2022.

*The data for November is incomplete

Figure 2.  Number of dengue cases and case fatality rates reported by year in Bangladesh from 1 January 2000 to 20 November 2022.

*Data up to 20 November 2022

Figure 3: Number of dengue cases reported by week for the period from 2017 to 2022 (until week 46, as of 20 November)

Figure 4.  Number of dengue cases by district in Bangladesh from 1 January to 20 November 2022. 

Epidemiology of dengue

Dengue is a viral infection transmitted to humans through the bite of infected mosquitoes and is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas. The primary vectors that transmit the disease are Aedes aegypti mosquitoes and, to a lesser extent, Aedes albopictus.

Dengue virus (DENV) has four serotypes (DENV-1, DENV-2, DENV-3, DENV-4) and it is possible to be infected by each. Infection with one serotype provides long-term immunity to the homologous serotype but not to the other serotypes; sequential infections put people at greater risk for severe dengue. Many DENV infections produce only mild illness; over 80% of cases are asymptomatic. DENV can cause an acute flu-like illness.

There is no specific treatment for dengue; however, timely detection of cases, identifying any warning signs of severe dengue infection, and appropriate case management are key elements of care to prevent patient death and can lower fatality rates of severe infection to below 1%.

Dengue was first recorded in the 1960s in Bangladesh (then East Pakistan) and was known as “Dacca fever”. The establishment of the Aedes aegypti mosquito vector and urban cycles have made dengue endemic in Bangladesh. The growth factor of dengue cases since 2010 appeared to be linked to regional rainfall patterns (May to September) and is coincidental with higher environmental temperatures. Bangladesh’s climate conditions are becoming more favorable for the transmission of dengue and other vector-borne diseases like malaria and chikungunya due to excessive rainfall, waterlogging, flooding, rise in temperature and the unusual shifts in the country’s traditional seasons. 

Public health response

• The Directorate General of Health Services (DGHS) has taken the following actions:
  • Repurposed six COVID-19 dedicated hospitals in Dhaka city for dengue case management
  • Established dedicated dengue wards/dengue corners in Medical College hospitals
  • Activated Control Rooms in all district and Medical College hospitals for sharing awareness information and situation update with the stakeholders (including media and local leaders) to access the information locally available
  • Conducted capacity-building activity on clinical case management by the inhouse trained facilitators at DGHS and trained 250 doctors and 300 nurses on clinical case management. 
• The MOHFW and WHO distributed a total of 284 000 non-structural protein (NS1) diagnostic kits to all the Upazila health complexes, district hospitals and Medical College hospitals in the country.
• Supplied adequate IV Saline and other supportive medicines for immediate response from the WHO-supported emergency buffer stock to health facilities all over the country.
• Blood banks are geared towards making platelets available for hemorrhagic dengue patients.
• Strengthened mass awareness campaigns – continued awareness through television and other mass media. The local ward counsellors have been trained in community awareness. The City Corporations carried out awareness programme and alerted building owners including buildings under construction to prevent water collection. Fines have been imposed on buildings where the Aedes larvae have been found.
• The local government engineering department (LGED) is leading vector control activities including the elimination of breeding sites and larvicidal and adult mosquito control using different insecticides such as Temephos and Deltamethrin among others.
• WHO supported pre-monsoon entomological survey through DFC, and is providing technical guidance to the outbreak response at the national level. 

WHO risk assessment

Bangladesh experienced a moderate rainfall during October this year which was unusual (monsoon is from May to September). Due to the untimely rainfall and favorable climate conditions, the density of the Aedes mosquito population is increasing. In addition, many people keep water in different containers like buckets and pots in their houses, enabling Aedes mosquitos to readily breed in such artificial collections of water.

A pre-monsoon survey carried out by the health directorate earlier this year found a higher density of Aedes mosquitoes in the capital compared to 2021. Experts in the Communicable Disease Control (CDC) unit of the Directorate General of Health Services (DGHS) predicted a worsening dengue situation this year in Dhaka city unless preventive steps were taken. The CDC unit revealed its most recent monsoon survey in September and found that mosquito density was twice as high in Dhaka city as in the pre-monsoon survey.

Dengue is a mosquito-borne viral infection caused by four dengue virus serotypes (DENV-1, DENV-2, DENV-3, DENV-4). The predominant currently circulating serotype in Bangladesh is unknown at this stage, but limited serotyping has detected dengue virus 3 (DENV-3) and dengue virus 4 (DENV-4). DENV-3 has been consistently predominant since 2019 but DEN-4 has not been reported for several years.

Dengue virus has the potential to cause epidemics resulting in high morbidity and mortality. There is no specific treatment. However, early recognition of dengue virus infection and appropriate clinical management can reduce disease severity and mortality among dengue patients. At present, the number of severe dengue cases and case-fatality rates appear to be increasing, likely due to late health-seeking behaviour and access issues.

With the receding COVID-19 pandemic, the travel restrictions have been lifted. This has led to the movement of people to and from Dhaka. Although there have been concerted efforts by the Local Government Engineering Department (LGED), City Corporations, and the Ministry of Health towards curbing the dengue outbreak in Dhaka in the past few months, yet the continued movements have led to an inflow of possibly infected individuals with a potential to contribute to dengue transmission cycles. Vector control activities have been less intense in the other districts of Bangladesh.

Dengue poses a significant public health concern for Bangladesh which experiences regular seasonal outbreaks of dengue. Furthermore, the clinical management of people who develop severe illnesses, often requiring hospital care, puts additional strain on an already overburdened healthcare system. 

WHO advice

The proximity of mosquito vector breeding sites to human habitation is a significant risk factor for dengue virus infection. Although dengue does not directly spread from human-to-human, Aedes species mosquitoes can become infected after biting dengue-infected individuals, thus creating a cycle of transmission capable of spreading dengue and leading to clusters of cases.

The prevention and control of dengue depends on effective vector control. WHO promotes a strategic approach known as Integrated Vector Management (IVM) to control mosquito vectors, including the mosquito genus Aedes (the primary vector for dengue). IVM should be enhanced to remove potential breeding sites, reduce vector populations, and minimize individual exposure. This should involve vector control strategies for larvae and adults (i.e., environmental management and source reduction, biological control, and chemical control measures), as well as strategies for protecting people and households. Bangladesh should implement the IVM strategy developed in 2021.

Vector control activities should focus on all areas where there is a risk of human-vector contact (place of residence, workplaces, schools and hospitals). Vector control activities can include covering, draining, and cleaning household water storage containers on a weekly basis. Space spraying with insecticide can be deployed as an emergency measure. Chlorination and application of suitable larvicides/insecticides for water storage in outdoor containers should also be considered.

Personal protective measures during outdoor activities include the topical application of repellents to exposed skin or on clothing, and the use of long sleeve shirts and pants. Indoor protection can include the use of household insecticide aerosol products or mosquito coils. Window and door screens, as well as air conditioning, can reduce the probability of mosquitoes entering the house. Insecticide-treated nets offer good protection to people against mosquito bites while sleeping during the day. Since Aedes mosquitoes are active at dawn and dusk, personal protective measures are recommended particularly at these times of day.

There is no specific treatment for dengue infection; however, early detection of cases, identifying any warning signs of severe dengue, and timely access to appropriate clinical management are key elements of care to reduce the risk for severe dengue complications and deaths due to dengue. Case surveillance should continue to be enhanced in all affected areas and across the country. Where feasible, resources should be allocated to the strengthening of laboratory sample referral mechanisms for the confirmation and sub-typing of the dengue virus.

WHO does not recommend any travel or trade restrictions be applied to Bangladesh based on the information available for this event.

Further information

• WHO factsheet: Dengue and severe dengue 
• WHO Q&A: Dengue and severe dengue 
• WHO Health topics: Dengue and severe dengue 
• Global Strategy for dengue prevention and control, 2012–2020
• Strong country capacity, improved tools and community engagement critical to enhancing dengue prevention and control
• WHO Manual for monitoring insecticide resistance in mosquito vectors 22 June 2022.
• Directorate General of health services (DGHS) Bangladesh, dengue daily situation report

Citable reference: World Health Organization (28November 2022). Disease Outbreak News; Dengue – Bangladesh. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2022-DON424