Changing Epidemiology of Dengue Haemorrhagic Fever in Indonesia

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Abstract
Dengue fever (DF)/dengue haemorrhagic fever (DHF) is a growing public health problem in the subtropics. Dengue was first reported in Indonesia in 1968 and since then the number of reports in the literature and the number of dengue virus (DENV)-infected cases reported by the Indonesian health authorities have increased. This review addresses the changing epidemiology of dengue in Indonesia by means of a chronological overview. Over time, the morbidity and mortality of dengue disease have increased and DHF epidemics occur throughout all the 29 provinces. The outbreak trend of DHF in the country has become irregular, with a high inter-epidemic background. All dengue serotypes are circulating, although severe disease is predominantly attributed to DENV-3. The case-fatality rate is dropping over time,
probably reflecting increased awareness and improved treatment protocols. An increasing percentage of adolescents and adults develop DHF relatively earlier in the course of the disease, compared with the days when DHF was considered a primarily paediatric illness. Many inter-related factors such as environmental, biological and demographic issues influence dengue epidemiology and transmission.
Keywords: Dengue, dengue virus, outbreak, epidemiology, Indonesia.

Introduction
Dengue fever (DF)/dengue haemorrhagic fever (DHF) is a growing public health problem in the subtropics.[1] In South-East Asia, with a total population of 1.5 billion, approximately 1.3 billion people live at risk of acquiring DF or DHF. Currently, DHF is the leading cause of hospital admissions and death among children in this region.[2] Major dengue epidemics date back to the late 17th century. However, the start of epidemics of severe dengue began in the South-East Asia region following World War II, when conditions for mosquito-borne diseases were favourable.[3] DENV infections during these latter epidemics were accompanied by severe haemorrhage, shock and vascular leakage. The first recorded DHF epidemic occurred in Manila, the Philippines, in 1953. Thereafter the epidemic spread quickly throughout South-East Asia and further west via India, Sri Lanka, Maldives and Pakistan, and
in the east to China.[3] Many factors are thought to be responsible for the global re-emergence of DF and DHF. These include major global demographic changes and worsening of health care systems and mosquito control programmes.[1,4] Indonesia is the largest country in the region with a population of 245 million. Almost sixty per cent of the people live on the island of Java, which is most severely afflicted by periodic outbreaks of dengue disease.[5] However, the disease is endemic in many large cities and small towns throughout the country and has also spread to certain smaller villages, where population movement and density are high.[6] Epidemic DF has been reported in all 27 Indonesian provinces, whereas in 1968 only two provinces had reported dengue cases.[6,7] This article addresses the epidemiology of
dengue in Indonesia by means of a chronological overview.

RESULT

Epidemics of DF and DHF have become an important public health problem throughout the Indonesian archipelago since it was first recognized in 1968. The epidemiology of DHF in the country is changing alarmingly given the increasing number of infections reported from all provinces. The outbreak trends of dengue, in general characterized as a cyclic pattern, have become somewhat irregular, with a high endemic background. A higher percentage of adolescents and adults seem to develop DHF.[5]The median age of DHF patients from Jakarta was 4 years and 11 months during the period 1979–1984.[6] Recent data from the Ministry of Health show an increasing number of DHF in children aged 15 years and older (unpublished data, Ministry of Health). Other reports also show this trend.[5,21] Furthermore, it may be stated that the reported case-fatality rate has decreased over time.

Increased awareness and better diagnostics have led to prompt recognition of the infection in health care facilities. Improved treatment protocols and local guidelines have contributed to this decline. Hopefully, the case-fatality rates will decline further in the near future. Concerning clinical outcome in terms of the rating of disease severity, it is not clear whether the ratios of DF, DHF and DSS have changed. Such information could not be clearly deduced from the reports studied. In the field, the disease severity is changing depending on outbreak severity and not following a regular pattern. However, there are some drawbacks in the presented data.

Besides more awareness, diagnostic tools and diagnostic facilities have improved over time, which undoubtedly have led to more reporting. Dengue outbreaks are now recognized earlier, and more sensitive and specific diagnostic tests help to confirm the disease. Case definitions of WHO, also used by the Indonesian Ministry of Health, are based on both clinical and diagnostic criteria. It is stated that any suspected or confirmed case should be reported. Because it is unlikely that many cases will have laboratory confirmation, the reported cases will not always represent the real situation. This accounts even more for a country with many epidemics and a high endemic transmission.

Not surprisingly, in the presented studies, the gap between suspected and confirmed cases is substantial. Moreover, perhaps some of the referenced older studies are less convincing. This is because they sometimes lacked a detailed method of selection and the diagnostic tools used then were less accurate. However, it is the only data we have. Multiple factors influence the occurrence of dengue epidemics, of which environmental, biological and demographic factors play a central role. The dengue incidence is associated with warmer, more humid climate.[4]Higher temperatures have been shown to enhance vector efficiency[33] and mosquitobiting behaviour.[34] Indeed, a marked increase in the rainfall and sustained higher temperatures compared to earlier years were the key factors during the Palembang outbreak.[21]
Furthermore, the epidemiological pattern throughout the year shows a peak incidence of DENV infections during the months of October through April, usually coinciding with the rainy season.[7,10,17,35] Endemic transmission requires, besides the mosquito vector, an immunologically susceptible population and the circulation of the dengue virus. The presence of multiple circulating strains and the introduction of new and more virulent viruses increase the incidence of DHF epidemics.[1] Some Indonesian studies clearly showed the relevance of secondary infections.[5,19] Of all the serotypes identified in Indonesia, DENV-3 was the most frequently
linked to the severe disease.[5,21,36]

Important demographic factors contributing to the transmission of dengue viruses also concern unprecedented population growth accompanied by unplanned and uncontrolled urbanization, a framework in which Indonesia perfectly fits. Dengue is on the rise in Indonesia. Hence, epidemiological surveillance must be established along with education campaigns and sustainable vector control programmes to control its transmission. To obtain good and trustworthy epidemiological data, surveillance centres should be well-equipped and should function in different provinces and report on regular basis to the Ministry of Health. The increasing number of severe, potentially fatal cases and the absence of an effective vaccine stress the need to continue all efforts in understanding the dengue epidemiology.