COVID-19 Causes False Positives for Dengue: Implications for Detection in Thailand

[@steveturner6732]

Hi Anthony, Nice job on keeping us updated with your perspective on what's happening in Thailand with respect to COVID-19. You are one of the very few sources of reliable and timely information specific to Thailand that is science-based and not simply click-bait hype, so I hope you keep up with updates, even though I'm sure this must be a lot of work for you. I think it's probably appreciated by a lot more people than those that take the time to "like" or comment.

[@steveturner6732]

I wonder if you can provide any links that show the number of people that are actually being tested here in the Kingdom? As you mentioned on your video "COVID-19 in Thailand Update Feb 29: What is a Person Under Investigation (PUI)?", it seems those numbers are not being published anymore, nor has there been any mention by officials about changed criteria for who is tested. (more) Personally, I'm concerned about this because of what's happening in the US right now. Only a week ago, the US President proudly proclaimed how there were only 15 cases in the US, but of course, that number has now jumped to 442 (as of today 08 March). It's pretty obvious that the initial low number was the result of low numbers of those actually being tested. In the US, I think the actual number of tests that have been conducted so far is only 1,895 TOTAL, compared to countries like South Korea, where over 10,000 tests are conducted DAILY! That just sounds insane! I really wonder what the situation is here in Thailand as to overall test numbers, and what the criteria is for who is tested and who is not? I mean, if only symptomatic PUI's are being tested, that does not seem proactive AT ALL! I know there was supposed to have been a big shake-up at Thailand's Ministry of Public Health a couple of weeks ago to implement more "aggressive" testing...so there was no shortage of talk...but what about the actual actions...I'm not hearing much in the news about that. >>> PS: I wrote this before watching your current video (COVID-19 Causes False Positives for Dengue: Implications for Detection in Thailand) since I was really responding toyour 29 Feb video...So this latest video answered my question in a lot of ways...BUT still, I am wondering if there is any official stats regarding number of tests actually being performed and the criteria.

[@AnthonyKuster]

Thanks for all your kind comments! What I can recommend for finding that answer is to check the Thailand Situation Reports issued through the WHO Thailand office (which is different from the MOPH daily Situation Reports). Occasionally they provide information about number of tests completed, which presumably is dependent on MOPH making them public. I'll post links to both below. What I can say is that the last time I saw hard numbers was in WHO Thailand Situation Report 7 (Feb 21, 2020) where 1489 samples were reported to have been completed. It's higher than I expected and appears to closely match the PUI on that date. One could infer that testing of all PUIs is now being completed and being completed in a timely manner. I will stress, however, that criteria for testing in Thailand still requires a narrow definition of exposure (i.e., travel to specific countries) and severe illness, so I believe the bulk of PUIs are those with severe pneumonia and most of those are from influenza. I will also stress that Thailand requires two positive results to come from two independent labs. Overall, I applaud this level of quality control but it's unclear how one positive and one negative would be handled (retesting? presumed negative?) and I've also already pointed out the uncertatinty in the methods as well as the false negatives demonstrated in the Singapore cases. WHO Thailand Situation Reports: www.who.int/thailand/emergencies/novel-coronavirus-2019/situation-reports MOPH Situation Reports (Thai): ddc.moph.go.th/viralpneumonia/situation.php MOPH Situation Reports (English, but 1 day delay): ddc.moph.go.th/viralpneumonia/eng/situation.php Case Definition and Testing Procedures for COVID-19 in Thailand: ddc.moph.go.th/viralpneumonia/eng/file/guidelines/G_en_21022020.pdf

[@AnthonyKuster]

Comments here about COVID-19 serological antibody testing are unrelated to what we're talking about it, which is false positives from dengue virus rapid diagnostic tests. It is true that the specificity of COVID-19 antibody tests (generally 95-99%) results in lower positive predictive values (i.e., the percentage of positive tests that have actually been infected) in low prevalence populations. HOWEVER, serological antibody testing (representing whether someone had previously been infected) does NOT "inflate case numbers," because case numbers are from diagnostic testing (conducted using PCR), which has a specificity of 100%. You will not get false positives from PCR unless you contaminate the specimen. Therefore, the "case numbers" represent a fraction of the total population that has been infected. On the other hand, despite the false positives from serological testing, the vast majority (>90%) of most countries' population remains vulnerable to SARS-CoV-2.

[@Renato_De_Bulhoes]

I from Rio, Brazil. We have almost no dengue cases in 2020, isn't wonderful ? So I've been questioning: where are the mosquitoes spending their vacations ?

[@bettinaheinz8459]

Fascinating. However, I don't think dengue tests were false positives. Different viruses can turn up together and interact. Something is involved that we don't know about yet. Dengue is mosquito-born and after acute phase can lead to myocarditis. The described cases are certainly thought provoking for me as a bioorganic chemist. Thanks!

[@AnthonyKuster]

Yeah, this is also super old. This was happening 1.5 years ago. I believe it has already been resolved, but I didn’t follow up.

[@januarysaintlouise1127]

My son had a history of dengue 5 yrs ago he is 15 now, my question is.. It is ok to take the covid-19 vaccine?

[@AnthonyKuster]

Thank you for your question. It has been speculated that antigens from SARS-CoV-2 and antigens from dengue virus can interact and increase the risk of thrombosis or hemorrhage (pubmed.ncbi.nlm.nih.gov/32946149/). However, there is no evidence of this occurring to date. Therefore, it doesn’t seem that there is any reason to change your vaccination plan based on last DENV infection. However, it is best to consult your physician. However, given previous DENV infection and then Covid vaccination, it is probably wise to avoid future DENV infection (this is true for anyone previously with dengue). Infection with multiple DENV types is high risk. Also, please note that there are many different Covid vaccines with four major mechanisms (viral vector, inactivated virus, protein, and mRNA). Due to already higher risk of thrombosis and hemorrhage from viral vectors, it may be wise to avoid them (J&J, Sputnik, AZ). If an option, seek alternatives to these.

[@jimbean4751]

But where are your false positives for Covid-19 numbers in your story?

[@AnthonyKuster]

The false positive is for dengue. Meaning that the case study highlighted here is about Covid has caused rapid treats for dengue to go positive when, in fact, they did not have dengue.