The Hindu

Dengue may pose risk of misdiagnos­is: study

‘Tests may return positive for COVID-19’

- Jacob Koshy

Can dengue be sometimes mistaken for COVID-19? Two independen­t research studies — one from a group in Israel and another from the Council of Scientific and Industrial Research-Indian Institute of Chemical Biology (CSIR-IICB) in Kolkata — show that tests specific to check for dengue sometimes led to a positive SARSCoV-2 test and this, the scientists warn, could lead to misdiagnos­es and skew public health responses in places where dengue is endemic and known to seasonally spike. This also prompts deeper investigat­ion into whether there are crucial similariti­es in the structure of these viruses.

The study from Israel, that was published in the peer-reviewed Clinical Infectious Diseases last week, describes testing 55 people, who had been confirmed to have a SARS-CoV-2 infection, for dengue. This was done using a serology test, or a blood-based test, where antibodies produced by the body during a dengue infection are used to probe for the presence of the virus. The principle is that when an antibody binds to a specific place on the virus, called an antigen, like a key that goes into a lock, a test is returned as ‘positive’. Antibodies and antigens are highly specific to each other.

Among the 55, 12 (21%) returned positive. Because the viruses that causes dengue and coronaviru­ses belong to entirely different families, it is not expected for one to show affinity to the other. Further, another lot of 95 samples obtained from patients diagnosed with dengue before September 2019, or the advent of COVID-19, targeting the spike (S) protein, was positive, the report adds.

Vulnerable areas

The study by CSIR-IICB used dengue antibody- positive serum samples from 2017 (pre-dating the COVID-19 outbreak) and produced false-positive results in SARS-CoV-2 IgG/IgM rapid strip tests, according to Subhajit Biswas, senior scientist at the IICB. This study is yet to be peer-reviewed and has not been published in a journal, but appears in Medrxiv, a preprint repository of scientific publicatio­ns that are open to public evaluation. “In places with recurrent epidemics of dengue, there is a risk that dengue may be identified as COVID-19 and so there ought to be confirmato­ry testing with other tests to rule this out,” he told The Hindu.

“22% testing positive is a significan­t number as the inherent error of the test itself is 4%. So we need to study further if the dengue virus is able to stimulate the body’s immune system to produce antibodies that could then bind to the coronaviru­s,” Dr. Biswas said, adding, “India and Brazil are highly endemic for dengue as are many parts of southeast Asia. Could that explain relatively lower per million mortality compared to Europe and the United States, where there’s little dengue? That may be worth investigat­ing.”

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