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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 8  |  Issue : 3  |  Page : 164-167

Association of serological parameters and platelet counts in dengue fever: A hospital-based study


1 Department of Microbiology, School of Medical Sciences and Research, Sharda University, Greater Noida, Uttar Pradesh, India
2 Department of Microbiology, Tomo Riba Institute of Health and Medical Sciences, Naharlagun, Arunachal Pradesh, India

Date of Submission12-Nov-2018
Date of Acceptance10-Jun-2019
Date of Web Publication05-Aug-2019

Correspondence Address:
Dr. Amit Kumar Singh
Department of Microbiology, Tomo Riba Institute of Health and Medical Sciences, Naharlagun, Arunachal Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijhas.IJHAS_88_18

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  Abstract 


BACKGROUND: Dengue fever (DF) is an acute febrile arboviral disease affecting the tropical and subtropical regions of the world. It is known that early and specific diagnosis of dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS), followed by supportive therapy, reduces morbidity and mortality. Serum levels of secreted NS1 positively correlate with viral titers and have been a useful tool in dengue infection (DI) diagnosis. NS1 detection is reported to be sensitive as well as highly specific. Apart from the dengue-specific parameters, platelet count is the only accessory laboratory test available in the peripheral areas that can support the diagnosis of DHF or DSS. In this study, we tried to correlate the platelet counts and immunochromatography (ICT)-based dengue serology tests.
METHODS: A total of 525 serum samples from clinically suspected DF were collected. The samples were tested immediately for NS1, immunoglobulin M (IgM), and IgG by ICT-based tests. Platelet counts of all the cases positive for any of the dengue parameters were noted. The statistical analysis was performed using Z-test.
RESULTS: One hundred and nine specimens were tested positive for either one or more of the three markers (NS1, IgM, and IgG). Platelet count <1,00,000/ml was noticed in 65 cases (%) of 109 dengue-positive cases. Of 79 cases who were positive for NS1 antigen only, thrombocytopenia was observed in 44 cases, whereas thrombocytopenia was observed in six of six cases positive for NS1 + IgM. The association of thrombocytopenia in NS1 + IgM-positive cases was statistically significant (Z = 2.125, P = 0.0331).
CONCLUSION: In the present study, association of thrombocytopenia in dengue parameter-positive cases was found to be highly significant. ICT is the only excellent tool as it is easy, rapid, and easily available in areas with poor resources. Apart from dengue-specific parameters, platelet count is the only accessory laboratory test available in the peripheral areas that can support the diagnosis of DI.

Keywords: Dengue, immunochromatography test, NS1 antigen, platelet count


How to cite this article:
Mohan S, Dutta R, Singh AK. Association of serological parameters and platelet counts in dengue fever: A hospital-based study. Int J Health Allied Sci 2019;8:164-7

How to cite this URL:
Mohan S, Dutta R, Singh AK. Association of serological parameters and platelet counts in dengue fever: A hospital-based study. Int J Health Allied Sci [serial online] 2019 [cited 2019 Aug 20];8:164-7. Available from: http://www.ijhas.in/text.asp?2019/8/3/164/263952




  Introduction Top


Dengue is an arthropod-borne disease caused by dengue virus (DENV, 1–4 serotypes) and is a major public health problem in most of the countries.[1] DENV belongs to the family Flaviviridae, and it is transmitted to humans by the Aedes aegypti mosquitoes.[2] On the basis of the neutralization assay data, four antigenically related but distinct serotypes (DENV-1, DENV-2, DENV-3, and DENV-4) can be distinguished.[3] DENV infection is a major cause of disease in tropical and subtropical areas.[4] Dengue is an endemic disease in most parts of India. It affects up to 100 million people annually, with 5,00,000 cases of dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) and around 30,000 deaths, mostly among children.[5] Since 2001, the total number of cases of dengue has increased significantly in India. Earlier, it was endemic in few states, but recently, it spreads to many states including union territories. Furthermore, it was restricted to urban areas but now has spread to rural areas of India.[6]

Majority of the cases of DENV infections may remain asymptomatic, but few may present with a wide range of clinical symptoms, ranging from mild fever (known as dengue fever [DF]) to a severe and sometimes fatal form of the disease known as DHF and DSS.[4]

Currently, for the diagnosis of DENV infections, methods available are virus isolation, detection of viral genome sequence by reverse transcription-polymerase chain reaction (PCR), and detection of DENV-specific immunoglobulin M (IgM) antibodies and NS1 antigen by enzyme-linked immunosorbent assay (ELISA) and/or rapid dengue immunochromatographic test (ICT).[7] The resource-limited settings as in primary health care usually depends on simple to perform and interpret diagnostic test to prevent the morbidity and mortality caused due to DHF and DSS.[8] NS1 is expressed on the surface of infected cells without forming part of the virion. Serum levels of secreted NS1 positively correlate with viral titers and have been a useful tool in dengue infection (DI) diagnosis.[9] Along with that, it does not have cross-reaction with those of other related flaviviruses.[10]

The “gold standard” tests for the identification of DI are not within the reach of peripheral and even most tertiary care laboratories. Detection of dengue-specific IgM/IgG has been the mainstay of diagnosis of DI. Antibody detection is an indirect method of diagnosis and therefore is prone to false-positive as well as false-negative results. NS1 detection is reported to be sensitive as well as highly specific.[11]

Apart from the dengue-specific antigen and antibodies, platelet count is one of the important predictive markers to help in early diagnosis of DI.[12] In primary care setup, platelet count is only additional test available that can support the diagnosis of DHF or DSS. A rough estimation of platelet counts by microscopy in resource-limited settings of primary care is helpful in diagnosis and monitoring the treatment of infection. In the present study, we have correlated the platelet counts, and dengue parameters detected by ELISA- and ICT-based dengue serology tests which will help the clinicians in primary care setup to diagnose and monitor the treatment of DENV infections.


  Materials and Methods Top


This was a prospective, cross-sectional, observational study conducted in the Department of Microbiology, Sharda Hospital, Greater Noida, Uttar Pradesh, India, a tertiary-care hospital from June 2017 to September 2017. A total of 525 serum samples collected from clinically suspected cases of dengue-like illness attending the outpatient departments and admitted in inpatient departments and sent for serological diagnosis of DI were included in the study. Ethical clearance was obtained from the Institutional Ethical Committee prior to the study.

The clinical criteria for selection of participants were made on the basis of the WHO criteria as follows:[13]

  • Dengue with or without warning signs:


    • Probable dengue


      • It presents as an acute febrile illness with two or more of the following – nausea, vomiting, myalgia, arthralgia, headache, retro-orbital pain, rash, and leukopenia.


    • Warning signs


      • Abdominal pain or tenderness
      • Persistent vomiting
      • Clinical fluid accumulation
      • Mucosal bleed
      • Lethargy and restlessness
      • Liver enlargement >2 cm
      • Laboratory: Increase in hematocrit current with rapid decrease in platelet count.


  • Severe dengue: Dengue with


    • Severe plasma leakage leading to


      • Shock (DSS)
      • Fluid accumulation with respiratory distress


    • Severe bleeding


    • Severe organ involvement


      • Liver: Aspartate aminotransferase or alanine aminotransferase >1000
      • Central nervous system: Impaired consciousness
      • Heart and other organs.


The samples were tested immediately for NS1, IgM, and IgG by ICT-based kit as well as by ELISA technique using ELISA kit. The tests were performed strictly as per the declared manufacturer's instructions. Platelet counts of all the cases positive for any of the dengue parameters were noted.

Statistical analysis

Statistical analysis was performed using the SPSS version 21 software (IBM). Z-test and Chi-square test were applied for the analysis of data to determine its statistical significance. P < 0.05 was considered as statistically significant.


  Results Top


A total of 525 serum samples collected from suspected DF patients were tested for dengue parameters, of which 109 specimens were tested positive for either one or more of the three markers (NS1, IgM, and IgG), as shown in [Table 1]. The data were analyzed to determine the association of thrombocytopenia with dengue parameter positivity [Table 2]. Platelet count <1, 00,000/ml was detected in 65 cases (59.6%) of 109 dengue-positive cases. Of 91 cases who were positive for NS1 antigen with or without antibodies, thrombocytopenia was observed in 54 cases, whereas when only the antibodies were considered, thrombocytopenia was observed in 11 of 18 cases positive for IgM/IgG/IgG + IgM. Statistically, there was no significant difference (Z = 0.418, P = 0.674) between two parameters in relation to thrombocytopenia.
Table 1: Comparison of dengue parameters

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Table 2: Comparison of platelet count and dengue parameters

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Of 79 cases who were positive for NS1 antigen only, thrombocytopenia was observed in 44 cases, whereas thrombocytopenia was observed in six of six cases positive for NS1 + IgM. The association of thrombocytopenia in NS1 + IgM-positive cases was statistically significant (Z = 2.125, P = 0.0331).


  Discussion Top


DF is an acute febrile arthropod-borne illness mainly affecting the tropical and subtropical countries.[1] The incidence of the disease has been increased significantly in the past years.[14] Due to its high mortality rate and to reduce the burden of disease, early detection of the disease by a rapid and sensitive laboratory assay is very helpful.

Dengue-specific antibodies usually appear near the end of a week of primary infection, and its detection has been the mainstay of diagnosis for a long time. In most of the secondary infections, both IgM and IgG antibodies do not appear before the 3rd day, thus creating a window period in both the types of infections. To overcome this, a new parameter available for diagnosis is NS1 antigen which is detectable in the serum from day 1 of fever in both primary and secondary infections and acts as a highly specific viral marker for the diagnosis of DIs.[12] Platelet counts are decreased in several other conditions such as some viral infections other than dengue, drug-induced thrombocytopenia, collagen vascular diseases, and idiopathic thrombocytopenia.[15] Therefore, association of platelet counts in cases of fever with dengue is an important marker to determine the severity of infections.

This study has been carried out at a tertiary care teaching hospital. It is worth mentioning here that most tertiary care hospitals do not have sufficient setup to perform viral cultivation. Therefore, applying gold standard tests in studies related to viral infections is out of reach of these centers.[6]

In this study, of 109 cases, 79 (72.4%) were positive for only NS1 antigen. As NS1 test is highly specific it can be stated that we would have missed the diagnosis in 72.4% cases if we had not included NS1 in the test panel. Kulkarni et al., Datta et al., and Shrivastava et al. have shown that NS1 was positive in 95 of 320 (30%), 140 of 600 (23.3%), and 15 of 91 (16%) cases, respectively, in their studies.[8],[10],[16] This supports the fact that a large number of cases would remain undiagnosed if NS1 is not included in the test panel. In this study, NS1 detection rate was 72.4%, which is much higher than the findings reported by other authors.[8],[10],[16] This may be attributed to the collection of large number of samples at the time of peak season of the infection. However, Jyothi and Metri and Mehta et al. have detected an almost similar rate of NS1 only positivity (62.9% and 64.5%, respectively) in their study.[5],[12]

NS1 alone or in combination with either IgM or IgG was positive in 91 cases (83.4%) in this study. Among two antibodies, IgG is a less reliable marker in the diagnosis of DI as it can be detected in clinical as well as subclinical DIs for several years.[17] Furthermore, it can be said that the level of IgG antibodies could be higher in endemic areas because of bites from infected mosquitoes.[12],[18] However, dengue-specific IgM is a very good indicator of recent infection. It may also be detectable in secondary DI. The diagnosis of DI by detecting antibodies alone depends mainly on rising titers of antibodies in paired sera. However, in routine clinical practice repeat testing with paired sera is not possible especially in the cases where the first test results were negative. When testing NS1 along with the antibodies, repeat testing with paired sera to determine the rising titer is no longer needed. Furthermore, it has increased the positivity rate of detection of DI.[11]

In this study, we determine the association of dengue parameter positivity with thrombocytopenia. The cases positive for NS1 antigen alone or with both antibodies showed no association with thrombocytopenia. However, NS1 + IgM-positive cases showed a statistically significant association with thrombocytopenia (Z = 2.125, P < 0.0331). Kulkarni et al. detected a consistent association of NS1 with thrombocytopenia when compared to antibodies.[8] In contrary, Mehta et al. have found a higher association of IgM antibody with thrombocytopenia, and Golia et al. have detected a higher association of IgG antibody with thrombocytopenia.[12],[19] The role of antibody in the pathogenesis of DF is well-known. Therefore, better association of platelet count with detection of antibody is consistent.


  Conclusion Top


In the present study, association of thrombocytopenia in dengue parameter-positive cases was found to be highly significant. Dengue is almost endemic throughout India. The resource-poor health-care system has to depend on simple to perform and easy to interpret laboratory tests for diagnosis. The highly sensitive techniques such as ELISA, viral culture, and PCR are not easily available for the diagnosis of DI. ICT is the only excellent tool as it is easy, rapid, and easily available in areas with poor resources. Apart from dengue-specific parameters, platelet count is the only accessory laboratory test available in the peripheral areas that can support the diagnosis of DI.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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