A profile of dengue cases admitted to a tertiary care hospital in Karnataka,southern India

Introduction

Worldwide, nearly 2.5 billion people continue to live at risk of contracting dengue infection. It is estimated that in 100 endemic countries, there will be 50 million cases and 24,000 deaths. The geographical spread, incidence and severity of dengue fever (DF), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) are increasing in central and South America, south-east Asia and the eastern Mediterranean and western Pacific countries. Cyclical epidemics of dengue have become more frequent over the past two decades. ¹ Treated DHF/DSS is associated with a 5% mortality rate and in untreated cases the mortality rates escalates to 50%.

The first confirmed report of dengue infection in India dates back to 1940s. Since then, more and more new states have reported cases of the disease, in both urban and rural environments, and have mostly struck in epidemic proportions inflicting heavy morbidity and mortality. ^2,3 The present study was undertaken in order to analyse the trend of the disease over the years and the outcome of the cases admitted to a tertiary care hospital in southern India.

Materials and methods

This retrospective study was conducted from January 2002 to December 2007 at the Kasturba Hospital, Manipal, a tertiary care teaching hospital which provides specialty health care to the four neighbouring districts in the coastal state of Karnataka. The state is located in southern India and lies between 11.5° and 18.5° north latitudes and 74° and 78.5° east longitudes. The major part of the state lies in the Deccan Plateau, mostly in rain shadow areas. We carried out the study in order to understand the trends and outcomes of patients admitted with a diagnosis of dengue, DHF and DSS according to the World Health Organization protocol. ⁴ Standardized dengue enzyme-linked immunoadsorbent assay immunoglobulin M antibody-positive (PanBio kit, PanBio Pty, Brisbane, Australia) cases were included in the study and analysed using a SPSS (version 13.5) package.

Results

Of the 344 cases, the largest number of cases (194, 56.4%) occurred in the 15–44 year age group and 24 (7%) were aged less than 5 years. The majority, 216 (62.8%), were males and only 128 (37.2%) were females. Most of the cases (219; 63.6%) were seen during 2007. The majority of the patients were agriculturists (106, 30.8%) and students (102, 29.7%). Many were cases referred from other districts (308, 89.5%), and only 36 (10.5%) were from within the district. Most of the dengue cases occurred during September (78, 22.7%; Figure 1). Of the total cases, 285 (82.8%) had dengue fever, 34 (9.8%) had dengue hemorrhagic fever and 25 (7.3%) had dengue shock syndrome. The average duration of the hospital stays was 6–10 days (204; 59.3%). There were nine deaths reported with the maximum number of deaths (four) in 2003 (Table 1).

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Figure 1

Monthly distribution of dengue cases during 2002–2007

Discussion

Dengue is an important emerging disease in the tropical and sub-tropical regions of the world. An analysis of the year-wise distribution of dengue cases in the study population showed that there has been a steady increase in the number of patients over the past few years. Of the 344 cases, 219 (63.7%) were reported in 2007 but only seven (2%) were reported in 2002. This may be partially attributed to:

An increased awareness of the disease;

In order to identify if there were any seasonal variations, the data was broken down on a month by month basis. It revealed a peaking of cases in September, i.e. after the monsoon season. There were two peaks, in June and September, which can be explained by the stagnation of water after two bouts of rainfall which facilitated vector breeding. The correlation between the occurrence of dengue and the monsoon season was evident and is further supported by similar findings in Kerala, ⁶ Ludhiana (Punjab) ⁷ and Karachi (Pakistan). ⁸ These findings indicate that preventive measures against dengue infection should be fully implemented after bouts of rainfall when the water became stagnant.

The female: male ratio in this study was 1:1.7. A similar pattern was also seen in the retrospective analysis of the north Indian dengue outbreak in 2006. ⁹ This can be attributed to a larger number of males in the Karnataka population. Our study revealed that the majority of the cases were seen in the 15–44 years age group (194, 56.4%). A comparison of cases in adults and children (<15 years) revealed that during 2002 to 2007 a disproportionate number of the cases were adults. Although there had been a dramatic increase in the total number of cases in 2007, there was no increase in the number of children affected. This pattern was also reported in the study conducted in Kerala.

True endemicity will be reached when the adult infection rate comes down and the child rate increases. ⁶ It is important to bear in mind that other infectious causes, such as typhoid, leptospirosis and enteroviral infections, are common in India and may lead to a delay in the diagnosis of dengue. Our study suggests that dengue in all its severe forms should be included in the differential diagnosis of patients with fever. This concurs with the conclusion of a report from a tertiary care centre in Pakistan. ⁸

Of the 344 cases, 63 cases had complications. The majority had pleural effusion 21 (33.3%), but the overall outcome of patient care was good – there were only nine deaths during the study period. The maximum number of deaths (four) were seen in 2003. In a report from Kerala, Kavitha ⁶ stated that in 2003, during a major outbreak, there were 623 patients and the case fatality rate was 13.2%. Although there were a greater number of cases in 2007 (219, 63.7%), the number of deaths was relatively less due to early diagnosis and prompt treatment. The vector control programme should lay a greater emphasis on activities such as intensive vector surveillance and the integrated vector control programme during the entire monsoon and peri-monsoon period.