Abstract
BackgroundDengue is the major mosquito-borne disease in Sri Lanka. After its first detection in January 2020, COVID-19 has become the major health issue in Sri Lanka. The impact of public health measures, notably restrictions on movement of people to curb COVID-19 transmission, on the incidence of dengue during the period March 2020 to April 2021 was investigated.MethodsThe incidence of dengue and COVID-19, rainfall and the public movement restrictions implemented to contain COVID-19 transmission were obtained from Sri Lanka government sources. A Seasonal Autoregressive Integrated Moving Average (SARIMA) model was used to predict the monthly dengue incidence from March 2020 to April 2021 for each of the country’s 25 districts based on five years of pre-pandemic data, and compared with the actual recorded incidence of dengue during this period. Ovitrap collections of Aedes larvae were performed in Jaffna city in the Jaffna district from August 2020 to April 2021 and the findings compared with similar collections made in the pre-pandemic period from March 2019 to December 2019.ResultsThe recorded numbers of dengue cases for every month from March 2020 to April 2021 in the whole country and for all 25 districts over the same period were lower than the numbers of dengue cases predicted from data for the five years (2015–2019) immediately preceding the COVID-19 pandemic. The number of dengue cases recorded nationwide represented a 74% reduction from the predicted number of dengue cases for the March 2020 to April 2021 period. The numbers of Aedes larvae collected from ovitraps per month were reduced by 88.6% with a lower proportion of Ae. aegypti than Ae. albopictus in Jaffna city from August 2020 until April 2021 compared with March 2019 to December 2019.ConclusionPublic health measures that restricted movement of people, closed schools, universities and offices to contain COVID-19 transmission unexpectedly led to a significant reduction in the reported numbers of dengue cases in Sri Lanka. This contrasts with findings reported from Singapore. The differences between the two tropical islands have significant implications for the epidemiology of dengue. Reduced access to blood meals and lower vector densities, particularly of Ae. aegypti, resulting from the restrictions on movement of people, are suggested to have contributed to the lower dengue incidence in Sri Lanka.
Highlights
Dengue is the major mosquito-borne disease in Sri Lanka
The densely populated districts of Colombo, Gampaha and Kalutara are located in the wet zone, while the Jaffna district in the northern Jaffna peninsula lies in the dry zone (Fig. 1)
Prediction of the expected number of monthly dengue cases from March 2020 to April 2021 Even though population movement restrictions to contain COVID-19 transmission were only implemented from 17 March 2020 onward, the entire period from 1 March 2020 to 30 April 2021 was used in our analysis because epidemiological and rainfall data were only available on a whole monthly basis
Summary
Dengue is the major mosquito-borne disease in Sri Lanka. After its first detection in January 2020, COVID-19 has become the major health issue in Sri Lanka. Sri Lanka is a dengue-endemic tropical island in the Indian Ocean in proximity to South India and lying between latitudes 5°55′ and 9°51′ N and longitudes 79°41′ and 81°53′ E. It has a population of 21.8 million, a land area of 65,525 km administrative districts, and is separated by its central hills into dry and wet rainfall zones (Fig. 1). Rainfall is the principal meteorological factor influencing the abundance of dengue vectors throughout Sri Lanka, so that monsoonal rains are followed soon after by a surge in dengue cases [5,6,7]
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