key: cord-0731485-wegwr2zm
authors: Biswas, Subhajit; Sukla, Soumi; Roy, Subrata; Nath, Himadri; Mallick, Abinash
title: Response to: Serological cross-reaction and co-infection of dengue and COVID-19 in Asia: Experience from Indonesia
date: 2021-02-05
journal: Int J Infect Dis
DOI: 10.1016/j.ijid.2021.01.063
sha: 425e61a6d1e66bba8fc17d64de69d8519df8251f
doc_id: 731485
cord_uid: wegwr2zm

nan

We congratulate the authors of the above article recently published in your Journal on their efforts to raise public health concern for COVID-19 and dengue detection in countries where both now co-exist.

Three cases were presented. One was described as the first report of dengue COVID-19 coinfection based on positive results in dengue NS1 and IgM tests; dengue serotying and detection of SARS-CoV-2 by qRT-PCR. The other two cases were diagnosed as dengue only by the aforesaid tests; but COVID-19 negative as SARS-CoV-2 qRT-PCR came negative.

Sera from all three cases cross-reacted in COVID-19 rapid tests. For the first case, this was obvious as antibodies to both viruses were present.

The authors concluded that the dengue sera in the last two cases gave "false-positive" results in COVID-19 tests (since they were SARS-CoV-2 negative by qRT-PCR) and explained that this "cross-reactivity" was due to antigenic similarity between these two viruses. However, we think that an alternative and equally plausible explanation could be that both these patients were silently exposed to COVID-19 beforehand; remained asymptomatic during viraemia for about three weeks or so (Zou et al., 2020) and subsequently turned SARS-CoV-2 negative by qRT-PCR due to virus clearance/low abundance (Wajnberg et al., 2020) .

Meanwhile, they developed COVID-19 antibodies, detectable for several months post infection (Ibarrondo et al., 2020) . In this phase, if they contract dengue, the reactivity in COVID-19 rapid tests are not necessarily due to "cross-reacting" dengue antibodies but could also be due to pre-existing COVID-19 antibodies (Clarke et al., 2020) . This is particularly possible for samples collected in the time frame, when both diseases were co-existent in the population.

Our same argument holds for the two Singapore case reports (Yan et al., 2020) , where in a reverse scenario, sera from COVID-19 RNA-positive patients showed reactivity in dengue rapid antibody tests despite being dengue PCR-negative. Singapore is highly endemic for dengue (Tan et al., 2019) . So, it cannot be ruled out that both elderly patients had contracted dengue in the past and had pre-existing dengue antibodies in their serum.

Nevertheless, we concur with the authors that there appears to be antigenic similarities between SARS-CoV-2 Spike and dengue envelope, as evident from our observation that archived dengue serum samples from 2017, pre-dating the COVID-19 pandemic, cross-reacted in COVID-19 rapid antibody tests (Biswas and Sukla, 2020; Nath et al., 2020a Nath et al., , 2020b , later confirmed independently by others (Lustig et al., 2020) . 

This is a correspondence and does not contain data that require ethical approval.

J o u r n a l P r e -p r o o f

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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