Southeast Asia at risk of missing coronavirus cases amid dengue outbreak: Experts

A woman holding her pet dog watches a municipal employee operating a fogging machine to kill mosquito larvae to fight the spread of dengue in the Philippines in 2019.

The concurrent outbreaks of dengue and Covid-19 in Southeast Asia will pose new challenges for authorities and health care workers, with experts warning that new coronavirus infections could slip through the cracks.

Their concerns were sparked by a March 4 report by Singapore-based doctors in medical journal The Lancet that pointed to the similarities between the mosquito-borne disease and the novel coronavirus - and how this could result in false-positive results for dengue.

"Dengue and coronavirus disease 2019 (Covid-19) are difficult to distinguish because they have shared clinical and laboratory features," wrote the group of authors from Singapore's National University Health System, Ng Teng Fong General Hospital, and the Environmental Health Institute.

The report cited the case of two Singaporeans who initially tested positive for dengue after rapid serological testing - a term usually used for antibody tests - but were later found to have been infected with Covid-19. Neither patient had travelled to areas affected by the coronavirus, but had exhibited symptoms such as fever and coughing.

"These are very common in all virus illnesses," said infectious diseases expert Leong Hoe Nam from Mount Elizabeth Novena Hospital. He added that muscle aches were another symptom exhibited by patients suffering from influenza, dengue, Zika or Chikungunya.

Leong said if dengue test results came back positive, doctors could jump to the conclusion that a patient had the disease, especially if they lived in an area that was a dengue hotspot. He added that it did not help that both outbreaks were occurring simultaneously in Southeast Asia.

Jeremy Lim, a partner at the health and life sciences practice of global consultancy firm Oliver Wyman, said the Covid-19 virus could be "quite a chameleon" in the early stages of infection, and could lead to some coronavirus cases being diagnosed as dengue.

"The complicated thing is that when people present to their general practitioners or to a hospital with fairly non-specific symptoms, you now have to worry about both," he said.

Lim explained that the immunoglobulin (or antibody) test for dengue looked at "certain protein spikes on the surface of these viruses".

"It's like a lock and key, and if [a virus] has enough notches that fit the lock, it will match. For dengue and the coronavirus, they have enough common notches that you can get a false positive," he said.

Responding to a query from the South China Morning Post, the World Health Organisation emphasised that dengue and Covid-19 were "two completely different viruses", pointing out that the former is a flavivirus while the latter is a coronavirus.

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"While the initial symptoms of both diseases can be similar, we can differentiate between the two as the disease progresses," it said. "The decision to order [a test for either disease] is made by the clinician and is based on the clinical presentation and other information including the epidemiological link and other exposure."

There has been a wave of new coronavirus cases in Southeast Asia over the past week. There are 160 confirmed cases in Singapore, while Malaysia and the Philippines have 117 and 35 respectively. Indonesia and Brunei have reported their first infections over the past week, with experts expecting numbers there to mushroom.

These countries are also grappling with explosive outbreaks of dengue, which is also known as "breakbone fever". There are some 390 million dengue infections around the world each year, according to an estimate cited by the WHO.

"Despite a risk of infection existing in 129 countries, 70 per cent of the actual burden is in Asia," the organisation said on its website.

Singapore's National Environment Agency noted that the city state had recorded 1,723 dengue cases in the first five weeks of 2020, up 63 per cent from the corresponding period last year.

Lim from Oliver Wyman said the prevalence of dengue infections and corresponding availability of test kits made it "much easier" to test for the disease, while "for Covid-19, you don't have a great test, and you're in shortage of supplies" - increasing the risk that patients would be wrongly diagnosed with dengue.

The authors of the Lancet report also stressed the importance of having affordable, readily available coronavirus test kits across Asia. "We emphasise the urgent need for rapid, sensitive, and accessible diagnostic tests for [Covid-19], which need to be highly accurate to protect public health," they said.

Leong from Mount Elizabeth Novena Hospital said the Covid-19 virus had "raised the bar of being a doctor".

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"Dengue has a plethora of signs and symptoms and [we have] to use all our senses, experience, and logic to ask if it is typical dengue," he said, explaining that it was not enough to use the dengue test as the sole criterion to determine if a patient had contracted the disease.

Ooi Eng Eong, deputy director of Duke-NUS Medical School's emerging infectious diseases programme, agreed with this take, adding that the choice of diagnostic tests must be guided by the patients' clinical presentation.

"Testing every fever patient for Covid-19 at this point when the disease is not as common as other viral infections would not be useful, and would add unnecessarily to health care costs," he said.

Oliver Wyman's Lim said the Lancet report was a good reminder for health care workers that lab tests were never 100 per cent accurate.

"We should maintain a high index of suspicion when the clinical picture does not match the lab finding," he said, suggesting that clinics and hospitals follow up with patients and continue monitoring them after the initial diagnosis.

"If the symptoms change and move away from what we are expecting, then we have to go back to the first diagnosis and ask ourselves [if] that could be something else," Lim said.

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This article was first published inĀ South China Morning Post.