# 2017 dengue outbreak in Sri Lanka

In 2017, there was a rise in the number of dengue fever cases reported in the island country of Sri Lanka. The peak of the outbreak occurred during the mid-year monsoon season with more than 40,000 cases reported in July alone, far exceeding historical highs. By the end of the year, the total number of dengue cases had risen to 186,101.
Forty-three percent of cases were recorded in urban areas of the Western Province, such as the Colombo district. The majority of dengue cases affected young people and school children. By the end of the year, the total number of dengue-related deaths reached 440.

## Background

In 2017, Sri Lanka experienced its largest outbreak of dengue fever, a neglected tropical disease, since the first recorded case in 1962. This biological hazard, transmitted via female mosquito bites, resulted in 186,101 dengue cases, a significant increase compared to previous years (see table below), and let to 440 deaths.
Annual Dengue Cases, 2010–2022 :
| Year | Number of cases |
| 2010 | 34,188 |
| 2011 | 28,473 |
| 2012 | 44,461 |
| 2013 | 32,063 |
| 2014 | 47,502 |
| 2015 | 29,777 |
| 2016 | 50,592 |
| 2017 | 186,101 |
| 2018 | 51,659 |
| 2019 | 105,049 |
| 2020 | 31,162 |
| 2021 | 25,067 |
| 2022 | 57,864 |

## Outbreak

Sri Lanka's Ministry of Health (MoH) reported an increase in dengue fever cases from January 2017 and peaking in July of the same year. The majority of cases were concentrated in the Western and Northern parts of the country, particularly in the urban Colombo district.
Reported Dengue Cases (2017) :
| Area | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Total |
| Sri Lanka | 10,927 | 8,724 | 13,540 | 12,540 | 15,963 | 25,319 | 41,121 | 22,270 | 9,519 | 6,614 | 8,868 | 10,753 | 186,158 |
| Colombo District | 2,734 | 1,900 | 2,467 | 2,570 | 3,333 | 5,372 | 7,471 | 3,620 | 1,251 | 823 | 1,131 | 1,602 | 34,274 |
| Gampaha District | 1,635 | 1,087 | 1,870 | 2,072 | 3,168 | 4,901 | 9,039 | 3,553 | 1,246 | 779 | 1,078 | 1,219 | 31,647 |
| Kalutara District | 581 | 448 | 836 | 739 | 946 | 1,248 | 2,612 | 1,477 | 663 | 337 | 528 | 546 | 10,961 |
The Government of Sri Lanka spent over $12 million (US dollars; USD) on outbreak control efforts, with support from non-governmental organizations (NGOs) like the Red Cross.

## Causes
### Climate

Sri Lanka's tropical climate offers prime mosquito breeding conditions.$^{[1}$ The 2017 monsoon rains (May–August) coincided with the peak of the dengue outbreak. Triggering floods and disrupting refuse collection, increased mosquito breeding sites.$^{[2][3]}$ However, annual rainfall and El Nino conditions were lower on average than previous years, suggesting that the climate was not completely responsible for the outbreak.$^{[4]}$

### Political

MoH failed to prepare and take appropriate mosquito vector control actions.$^{[5][6]}$ Insufficiencies in the virologic surveillance program failed to identify dengue serotypes and genotypes$^{[5][2][7]}$ leaving Sri Lanka unprepared for new strains (DENV-2), for which their population would have little immunity.$^{[8][4][7]}$

### Socio-economic

Sri Lanka is a middle-income country with a gross domestic product (GDP) per capita of US$12,600 (2017).$^{[9]}$ This restricts investment in healthcare infrastructure, resulting in an overstretched healthcare system.$^{[2]}$ High urban population density in Western districts created a higher probability of transmission.$^{[4]}$ In 2017, 42% of Sri Lankans were in extreme poverty (below US$5.50 a day) which limits a family's access to healthcare and increases the risk of disease.$^{[9][10]}$ Regional disparities, due to the Sri Lankan civil conflict (1983–2009), displaced people to internally displaced persons (IDP) camps and marginalized ethnic groups (Tamils) in North and Eastern districts, reducing support and increasing disease risk.$^{[11][12]}$

## Impacts
### Short-term impacts

The fever brought an unexpected high death toll. Along with the death toll, it also caused disruption to workplaces, household income, and education as the majority of cases were people aged 10–29. Direct and indirect impacts of the dengue outbreak affected 600,000 people in all 25 districts, prominently in urban areas. Some districts, however, may have been under-reported due to ethnic marginalization and the presence of IDP camps. Dengue treatment put pressure on national economic resources, costing Sri Lanka LKR 1.938 billion (US$12.7 million).

### Long-term impacts

Today, dengue cases are declining in Sri Lanka, with 25,067 total cases in 2021. Dengue is still present with new strains (serotypes DENV-3 and DENV-4) becoming more prominent and threatening future outbreaks. Combined with the COVID-19 pandemic, there is still immense pressure on healthcare and trade networks. The year 2022, has seen an economic crisis and severe food insecurity in Sri Lanka; the dengue outbreak would be a contributing factor.

## Future

Climate change models suggest that Sri Lanka's climate is becoming more conducive to mosquito breeding and this combined with economic instability could trigger a future epidemic. There is a possibility that a cycle of disease, poverty, and food insecurity may be challenging to break. However, this could be mitigated if the MoH, supported by institutions like the World Health Organization (WHO), engage in proactive strategies. A licensed vaccine (Dengvaxia; made by Sanofi Pasteur) is now available, at the cost of US$78 per person - with five more in development. However, Sri Lanka's current expenditure is US$161 per capita on healthcare (2021), and the vaccine is a significant proportion of that budget and in uncertain economic times, may not be a priority.