Clinical and seasonal pattern of dengue in a tertiary care hospital of South West India

Introduction

Dengue is an emerging global viral disease with an increase in incidence of 30 times in the past fifty years. Nine countries were affected before the 1970s but now more than 100 counties have severely been affected with dengue epidemics with the Southeast Asian region and the Western Pacific region being the most severely affected. 390 million cases of dengue occur annually with 96 million showing clinical manifestation.¹

The first case of dengue was reported by Benjamin Rush in 1789. Up until the middle of 20^th century it was restricted to few geographical locations, but with the population movement during the Second World War there were recurrent epidemics with the re-emergence of the disease.²

Even though the first epidemic of dengue was reported from Chennai in India, the virologically proven epidemic occurred in Kolkata in the 1950s. There were cases of dengue hemorrhagic fever and dengue shock syndrome in Delhi and Lucknow in the year 1996, thereafter with a cyclical pattern occurring every 2-3 years.²

In the past 20-30 years it was mostly restricted to only a few states of South and Northern India but in the last decade it has affected almost all the states of India.³

Dengue is viral vector borne disease spread by the day-biting endophilic Aedes mosquito. Its clinical features tend to be vague and nonspecific, ranging from fever to hemorrhage to shock with no specific treatment but supportive care.^4,5

Geographically, dengue is more prevalent in tropical countries like India. With that background understanding, we conducted our study in the coastal part of South India where developmental activities are on a rise with rapid urbanization where the study population is at a high risk of being affected with dengue. Our study was conducted to determine the socio-demographic and clinical profile along with the disease outcome of dengue patients. As information regarding the trend, burden and distribution of the disease is vital to plan disease control strategies and optimum utilization of the resources, our study aims to further contribute to the knowledge base regarding this disease.

Methods

Results

Seasonality

Dengue being a vector borne disease was expected to boom in accordance with the monsoon seasons and our study was able to confirm this. As depicted by Figure 1 [Month wise distribution of dengue cases (n=401)], most of the cases were found to have been admitted during the months of June and July with a declining trend both pre- and post-monsoons. The months of January to April were shown to have a consistently lower admitted case load. Figure 2 represents the year wise distribution of Dengue cases admitted in the hospital.

Figure 1. Month wise distribution of dengue cases (n=401).

Figure 2. Year wise distribution of dengue cases (n=401).

Discussion

Dengue is an upcoming and swiftly spreading vector borne disease that has taken strong hold in India.⁴ Owing to the complicated interplay between the host, agent, vector, and environmental conditions, the number of cases in India has consistently increased substantially over the past ten years.⁶ It is now even considered as a hyper endemic disease in certain parts of India. As Das et al. demonstrated in their study, the available data on dengue prevalence in India is just the tip of the iceberg and that further weighs down the preventive measures taken to reduce the brunt of the burden.⁷ Having recognized the need for comprehensive stratified data on dengue prevalence and its trends to further the knowledge database in Indian population, we focused our study to assess the various clinical, sociodemographic and climactic factors.

Our study was able to demonstrate a significant male preponderance (male = 61%, females = 39%) in cases of dengue reporting to this hospital with a male to female sex ratio of 1.5:1. Similar observations have been made by a multitude of studies, yet a conclusive reasoning has not yet been attributed to this trend.⁸ Doke and Pawar has attributed this finding to the nature of dressing among women which reduces the amount of skin exposure.⁹ Other studies have explained this as a product of reporting bias among females as it has been seen that traditional practitioners are the first point of contact for the large majority of symptomatic female population.¹⁰ A few studies even postulated that this disparity could be due to the skewed sex ratio leaning towards the side of males in the general population.¹¹

Apart from the male preponderance, our research found that the productive working class aged 20-40 years was the age group most affected. Owing to the declining rate of incidence with advancing age, it could be said that infants, adolescents and young adults are at higher risk of developing dengue. Similar trend has been observed in other studies wherein they found that dengue is a disease that primarily affects the children and the young adults.^3,12–15

Combined, the age and sex distribution findings could be attributed to the complex interplay between outdoor nature of work (among men),⁹ dressing patterns (among women), skewed sex ratio and diurnal feeding habbits of Aedes aegypti.⁴

Most of the cases were found to have occurred in the months of June and July, with the maximum being 120 cases. A study conducted by Kumar et al. in a coastal city of Karnataka revealed the maximum cases were found to have occurred in the month of September while a meta-analysis conducted by Ganeshkumar et al. found that most cases were seen in the monsoon and post monsoon seasons.^13,16 The peri-monsoon seasonality of dengue has also been promptly emphasized by a number of studies which implicates that there is a strong correlation that exists between temperature and humidity to the favourable breeding conditions for the mosquitoes.^3,13,14 During rainy season environmental changes such as artificial water stagnation, especially in low lying areas, labour settlements and small collection of water in tyres and flowerpots act as favourable breeding grounds for the vector which conclusively explains the precipitous climb of dengue cases during June to September.¹⁴

The clinical picture of patients in our study revealed that fever was present in almost all cases (99.3%) followed by chills and rigor (63.8%). Haematological symptoms included hematemesis and haematuria which were present in 12% and 7% of cases respectively. A meta-analysis conducted on a global scale on dengue outbreaks came to an almost similar picture with fever (98.1), chills (65.3), myalgia (64.2), arthralgia (53.6), body pain (67.2), vomiting (39.8) etc. with similar haematological symptoms like haematuria and hematemesis which were seen in 5% and 13.4% of cases respectively.¹⁷

Liver functions test showed abnormal rise in almost 99% of patients of SGPT and SGOT levels but SGOT levels were more prominent in most patients as compared to SGPT, similar research done in Punjab in 2007 had similar results with 98.9% of patients showing a rise in either of SGPT or SGOT levels indicating a strong heptic predeliction for dengue virus.¹⁸ A dedicated study regarding dengue and hepatopathy also revealed similar results of elevated SGOT and SGPT with the former being more elevated than the latter.¹⁹

Thrombocytopenia is the most common laboratory finding in dengue patients and is referred to as an early marker and prognostic factor for the management and recovery of dengue fever.²⁰ Of 384 dengue patients studied, 368 patients had thrombocytopenia (platelet count less than 100,000 per mm³).

Our study revealed a seropositivity rate of 23.94% which is similar to another study conducted by Kalita et al. where they repoted a seropositivity of 14.85%.²¹ Along with having a low seropositivity rate, it was seen that High IgM prevelance was noted in our study. As concluded by Eshetu et al., high IgM prevelance is indicative of active transmission of dengue which could account for the hyperendemic status of dengue in Southern India.²²

Our study included 401 serologically confirmed dengue cases out of which 367 cases (91.5%) were found to have recovered completely. Seven deaths were recorded (1.7%), and 27 cases (6.8%) were found to have been discharged against medical advice. A meta-analysis conducted in India, found that the pooled CFRs of the studies was 2.6% which was in line with findings of the present study.¹⁶

Conclusion

Dengue remains to be a major public health problem in this part of the globe, affecting mainly the working age group. With vague nonspecific clinical features combined with low seropositivity rate, it is of paramount importance to keep dengue as a key differential when a patient presents with febrile illness of nonspecific nature. High IgM seropositivity also hints at the fact that a strong and robust vector control programme must be implemented to at least make a dent in the hyperendemic status of dengue especially during the monsoon seasons.