Introduction

Dengue is a tropical disease that is transmitted by the bite of the Aedes mosquitoes carrying the virus.

Approximately 40% of the world’s population or 3.6 million individuals reside in regions where they are at risk of contracting dengue fever. 

Many individuals may not develop any symptoms, or may present with only a mild illness when exposed to the dengue virus. However, if symptoms present, those typical of dengue fever include a sudden high fever (104°F or higher), nausea and vomiting, rashes, headaches, eye pain, joint pain or muscle pain. It is important to get tested for dengue if you are suffering from these symptoms. A rapid diagnostic test for dengue can help in early diagnosis and lead to improved clinical care and better outcomes.

Understanding the Rapid Diagnostic Tests for Dengue

A dengue fever test determines if you carry the virus by testing a sample of your blood. If you have symptoms of dengue fever and have been in an area where mosquitoes are carrying the virus, you should take the test. 

The diagnosis of dengue is made conventionally by using techniques such as polymerase chain reaction (PCR) or virus isolation. However, these methods prove to be expensive, time-consuming, and need certain specialised tools and expertise. To overcome these drawbacks, rapid diagnostic tests (RDTs) for dengue were developed that detect viral antigens (viral particles that trigger your immune system) and antibodies (proteins produced by your immune system to combat the virus) in your blood.  RDTs are simple to perform and include antigen tests (NS1 antigen test) and/or antibody tests (IgG and IgM tests) which help to identify dengue NS1 antigen as well as IgM and IgG antibodies respectively. Based on your symptoms and your condition, it may be recommended to do either antigen or antibody test or a combination of both tests. The sample used can be whole blood, serum, or plasma. 

With reliability in testing, quick results, and ease of use, RDTs can help in dengue monitoring and control programs by promptly and accurately confirming dengue infections. Early diagnosis also helps initiate timely clinical intervention for effective management of infection and prevent complications. 

When should I do the Rapid Diagnostic Test for Dengue

Rapid diagnostic tests are becoming more popular for confirming recent dengue infections because of their rapid turnaround time (results in less than 30 minutes) and ease of use.

The dengue antigen detection (NS1) test reveals accurate results in the first 5 days after the onset of symptoms. Hence, it is recommended to take the NS1 antigen test if you are facing any of the typical symptoms of dengue. However, this test is not recommended after day 7.

The antibody tests on the other hand, should best be taken 4 days or more following the onset of your symptoms for maximum accuracy as it takes time for your body to produce the necessary antibodies (IgG and IgM). During a primary infection, IgM levels are very high whereas during a secondary infection, high levels of IgG is noticed. Hence, based on the antibody levels, RDTs can be used to distinguish primary and secondary dengue infections. Antibody tests are most accurate when done four days of the onset of your symptoms.

Interpretation of results

RDTs are being used to help identify recent as well as past infections. IgM can be detected from the 3rd to 5th day of illness and can persist up to three months. IgG appears from the 14th day of infection and lasts for life. However, in patients with secondary dengue infection, IgG is detected within 2 days of illness and it may not be accompanied with a positive NS1 or IgM result. Hence, preliminary dengue diagnosis from the acute to convalescent stages of dengue infection can be made using simultaneous testing of NS1, IgM, and IgG.

The results of the rapid diagnostic tests for dengue can be interpreted as follows:

  • NS1 positive: Presence of dengue infection.
  • NS1 negative: Does not rule out the possibility of dengue (IgG and IgM should be checked)
  • IgM positive: Indicates primary dengue infection
  • IgG positive: Indicates secondary dengue infection
  • IgG and IgM positive: Indicates end stage of primary infection and early stage of secondary infection
  • IgG and IgM negative: No dengue infection. 

Accuracy of Rapid Diagnostic Tests for Dengue

While they do not distinguish between serotypes, rapid antigen tests like the NS1 rapid diagnostic test, can diagnose dengue infection with a general 100% specificity (accuracy in identifying individuals without the disease) and a respectable sensitivity of 71 to 80% (ability to correctly identify patients with the disease).

IgG levels frequently last a lifetime and can be used to detect prior dengue virus infection, while IgM levels can become undetectable after 3–6 months. Therefore, dengue virus specific IgG antibodies function as a marker for previous dengue infection in order to detect past infections.

Hence, the best way of diagnosing dengue illness, both early and late, is to test for both IgG/IgM antibodies and the NS1 antigen.

Use in resource-limited settings

Laboratory diagnostic resources are scarce in many dengue endemic locations, and in such cases, often doctors diagnose dengue infection only on the basis of clinical signs and symptoms which can be misleading. RDTs provide the best opportunity for point-of-care diagnosis and serve as a more reliable method for assessment of dengue. These can also be beneficial for emergency or preliminary medical screening in cases of outbreaks.

Hence, in resource-limited clinical settings, rapid diagnostic tests are a fast and easy way to diagnose dengue infection, where patients can receive their results within 30 minutes.

Conclusion

Early diagnosis and communication are essential for the implementation of early management and vector control strategies. Since the symptoms of early dengue overlap with those of many other fever infections, definitive tests are helpful for confirmation. With results obtainable under 30 minutes and ease of use, RDTs are highly beneficial in resource limited settings for the effective management of dengue. If you suspect you have dengue, get a rapid diagnostic test done today and stay healthy!

References

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