Serodiagnosis of Dengue in Paediatric Patients Importance of NS1 Antigen.

INTRODUCTION : Dengue is a re-emerging, mosquito-borne viral disease in the world. Dengue fever (DF) and its severe forms like dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS) have become major international public health concern. Children are at higher risk and the mortality rate during secondary infection is nearly fifteen times higher than the risk in adults. Since there is no immunoprophylaxis or specific antiviral treatment available, timely and rapid diagnosis plays an important role in patient management and application of control measures to prevent high morbidity and mortality. Since differentiation of dengue from other febrile illnesses in acute phase is clinically difficult, definitive and early diagnosis relies on laboratory tests which is important in the therapeutic intervention to decrease morbidity and mortality. Due to the rising importance of early and prompt dengue infection detection, this study was aimed to analyze the importance of NS1 antigen detection in early diagnosis of dengue and its correlation in primary and secondary infection. AIMS AND OBJECTIVES : 1. To study the prevalence of dengue in paediatric age group. 2. To study the importance of NS1 antigen in the diagnosis of dengue infection. 3. To demonstrate the importance of paired serum samples in the interpretation of dengue infections. MATERIALS AND METHODS : This study was conducted at Tirunelveli Medical College Hospital, Tirunelveli, among the dengue suspected paediatric cases admitted in the hospital. The study period was from August 2011 to January 2012. A total of 110 blood samples were collected from sixty five children, 45 had paired sample. Inclusion criteria: 1. Paediatric patients (0-12years), 2. Children admitted with acute febrile illness with two or more of the following features of WHO criteria- headache, myalgia, retro orbital pain, rash, haemorrhagic manifestations and thrombocytopenia. Exclusion criteria: 1. Febrile cases without the above features, 2. Haemorrhagic conditions without symptoms of Dengue fever, 3. Patients with clinical evidence of respiratory tract infection, urinary tract infections, acute diarrheal disease, injury, sepsis, or other apparent causes of fever were excluded. All the samples were tested for NS1 antigen, IgM and IgG in the Microbiology laboratory, Tirunelveli Medical College Hospital, Tirunelveli. RESULTS : Out of 40 cases, 19 (46%) were in the age group of 5 to 8. In this group 14 (74%) had secondary dengue infection. More number of males was seen in both primary and secondary infection compared to females. But statistical analysis using Fisher exact test showed that the difference was not significant (p>0.05). 21 (51%) cases had a platelet count of less than 50000 cells. Of which 14 (58%) cases were seen in secondary infection which is statistically significant (p 0.05). 21 out of the 33 (64%) cases had a haematocrit of more than 35 in secondary infection. Analysis by paired t test showed this to be significant (p<0.05). Three out of the 5 (60%) secondary dengue cases had WBC of less than 4000. More cases had pleural effusion in secondary infection and was statistically significant (p<0.05). CONCLUSION : This study highlights the combined use of NS1 antigen and IgM antibody in the diagnosis of dengue infection in the acute phase. Testing of paired sera is essential in diagnosis of dengue infection and differentiating primary and secondary dengue infection. More NS1 positive cases were seen in days 5 and 7 only. It was low in the first five days of illness. IgM was found to be more positive than NS1 in samples collected after the fifth day of illness. More number of secondary dengue infections was noted in the study. High NS1 positivity was noted more in primary dengue infection than secondary dengue infection. The low positivity of NS1 would have been due to immune complex formation as more secondary cases were observed. It would have also been due to low viremia or due to the virus serotype which was not confirmed.