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Correlation of NS1 Antigen Positivity Performed by Immunochromatographic (Rapid Card Test) with Collection of Blood during First Week of Fever in Clinically Suspected Cases of Dengue Patients in a Tertiary Care Medical College Hospital

NS1 antigen, known as Non Structural antigen is an important antigenic component of Dengue Virus. Dengue virus is transmitted by bite of Aedes aegyptii mosquito. Hemorrhagic manifestations and shock syndrome are most dreaded complications of Dengue IgM antibody is produced in acute phase and IgG in later phases of Dengue and may remain for very long periods.


INTRODUCTION
Dengue fever is transmitted by bite of Aedes aegyptii mosquito. This mosquito bites during day time and has white stripes on its legs. The saliva of biting mosquito has infective form of virus which is transmitted during blood meal. Dengue is a mosquitoborne disease affecting humans mainly in tropical and subtropical regions of the world [1]. It is an increasing public health concern in urban and suburban areas causing severe morbidity and mortality [2][3][4]. Globally, WHO has estimated that around 3 billion people reside in areas where there are risks of exposure to dengue virus and nearly 50 million people are infected with dengue virus every year [5][6][7]

MATERIALS AND METHODS
A comparative analysis of Serology samples collected for NS1 antigen by Rapid card test for the period from June 2017 to December 2017 in Department of Microbiology, Central services laboratory of Karpagm Faculty of Medical Sciences and Research, Othakalmandapam, Coimbatore was made with date of sample collection from clinical history and date of development of fever as mentioned in clinical history given by patient.
Blood sample collected was sent to Serology where after centrifugation it was used in Rapid card test using Immunochromatographic test for NS1 antigen.
Results: A total of 120 samples of Blood collected from suspected cases of Dengue with symptoms of Fever during the period from June 2017 to December 2017 formed the basis of study. Samples studied included from age group between 7 years and 60 years. Immunocompromised patients and infants were excluded from this study group.
Age wise positivity for NS1 antigen (Table 1), Sex wise percentage of Ns1 Positivity ( Table 2) and Period of sample collection since development of fever with NS1 positivity (Table 3) were the main parameters of study.

DISCUSSION
Dengue fever known as " Swaheli Ka Denga Pepo" meaning sudden seizure by Demon ,is also known as Break Bone fever. In extreme conditions it may lead to Shock syndrome.
Epidemics of dengue infection are showing an increasing trend in recent years. To date, there is no specific treatment for dengue virus infection. However, early diagnosis will help in the timely implementation of appropriate treatment, thereby greatly improving the outcome of the disease and also for effective public health control of dengue outbreaks [7, 10]. There are various methods available for diagnosis of dengue virus infection. Virus detection by tissue culture and immunofluorescence gives definitive identification of the dengue virus serotype. Virus isolation, even though considered the "gold standard" for the diagnosis of dengue infections, requires early acute sample (0-5 days post onset), requires expertise and appropriate facilities, time-consuming, expensive and laborious [15]. NS1 antigen detection is a useful tool for initial and early diagnosis of Dengue and this helps the patient and prevents them from landing in Shock syndrome (12, 13).
The Current study shows a very strong correlation between Period of sample collection since the development of fever and NS1 positivity by card test. For making a better statistical analysis and correlation, only 20 samples were selected based on duration of fever obtained from clinical history. It is evident from this study that as days progressed since the development of fever, NS1 antigen positivity rate dipped.

CONCLUSION
Dengue remains an Escalating problem all over the world but especially in Tropical Countries (11, 14).There is a severe impact on economy, morbidity and mortality in Developing countries which are located in the Tropics (15).