Suburban

Diagnostic Trends in Dengue – From Serology to PCR

Dengue: An overview

Dengue is a vector-borne disease that is a major public health threat globally. It is caused by the Dengue virus (DENV, 1–4 serotypes), which is one of the most important arboviruses in tropical and subtropical regions. Both Aedes aegypti and Aedes albopictus are the main competent vectors for Dengue virus in India.

Epidemiology:

With a constant rise in the number of cases being reported, Dengue has broken all the myths of seasonal uniformity, no more being just a monsoon fever

Below is the Real World evidence of a study conducted at Suburban Diagnostics from June 2019 to October 2019 for
diagnosis of Dengue.



Discussion:

Evidently, the number of Dengue cases this year, have shown an upsurge in the months of September and October, with
October leading the trend with 5767 tests taken and 1813 positive cases, a significant 31% positivity rate.

Interestingly, the positive rate of Dengue cases has shown a notable rise when compared with the previous year, irrespective of the test methodology being used. NS1, IgM and PCR, all the 3 commonly preferred diagnostics tests for Dengue have shown a positivity rise from 2018 to 2019, for the study period of June to October.

Although, it would be incorrect to associate Dengue to be a monsoon fever, rainfall has always been a driving factor.

This atypical rise of Dengue with a higher overall incidence in October could be driven by a heavier and prolonged monsoon this year.

While the incidence and prevalence rate for Dengue has been changing for the worse, one good change that we hope to see is the diagnostic approach towards this.

Serology tests like Dengue NS1 and IgM have become a practice. With rapidity of cases, comes the urge to have a quicker treatment initiation. Diagnosis, rather early diagnosis, plays a vital role here hence this is the correct time to move towards molecular diagnostics.

As per CDC guidelines, Dengue virus-specific IgM typically develop towards the end of the first week of illness.

However, patients with symptoms of Dengue can be tested with both molecular and serology tests during the first 7 days of illness.

As per the study conducted at Suburban Diagnostics, a sharp detection rate was observed with PCR as with NS1 and IgM.

October came with many learning for diagnosis of Dengue. A considerable positivity rate of 35% was observed when tested by PCR as with NS1 (33%) and IgM (30%).

Summary:

With this in-house study at Suburban Diagnostics, we would like to summarise with CDC recommendations as below:

  • NS1 is detectable during the acute phase of Dengue virus infection.
  • For symptomatic cases, Dengue virus RNA can usually be detected by molecular tests for the first 1-7 days in the course of illness.
  • Molecular tests are as sensitive as serology, if not better during the first 7 days of signs and symptoms.

Under this study, we have been able to identify 7 cases, where NS1 gave a negative result, but PCR stood positive.

Interestingly, we were also able to identify 3 cases were FD5 was negative but NS1 stood positive.

It is encouraging to note a significant shift from rapid card test towards ELISA based tests for Dengue. However, it is always
better to explore other approaches for a better insight.

Hence, the importance of a methodology of a test is at par with that of it’s indication.

Conclusion:

PCR based tests like FD5 involve studying genetic material from biological samples providing clinical benefits as below:

  • If Dengue stands negative, other possible causes like Chikungunya, Leptospirosis, Malaria and Typhoid can also be detected within the same period of 0-7 days and the same sample.
  • Common cases of co-infections as observed with Chikungunya and Dengue can be detected by adopting PCR based tests.
  • In cases of overlapping signs and symptoms, PCR simplifies the process of diagnosis by detecting the exact cause and assuring rapid diagnosis.

With further development in PCR and scope for data analysis, we shall continue such studies to be able to impact medical
outcome with precise diagnosis.



The following is an interesting insight of geographical spread of Dengue which was observed in Mumbai from June
2019 to October 2019.


References:
https://www.cdc.gov/Dengue/healthcare-providers/diagnosis.html
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5583666/
https://www.ncbi.nlm.nih.gov/pubmed/20727470
https://apps.who.int/iris/handle/10665/44188
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5583666/

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