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Cold symptoms that people normally 'shrug off' make mild cases of COVID-19 hard to detect: Experts

Cold symptoms that people normally 'shrug off' make mild cases of COVID-19 hard to detect: Experts

File photo of a medical staff wearing protective clothing during a demonstration of the polymerase chain reaction (PCR) swab test for the COVID-19 coronavirus. (Photo: AFP / Philip Fong)

SINGAPORE: Some patients with mild COVID-19 symptoms may have only had a slight fever, according to preliminary findings from a local study, which helps explain why coronavirus cases have sometimes been hard to detect.

On Thursday (May 28), authorities said that among pre-school staff members, 13 individuals have tested positive for COVID-19 out of more than 33,000 tested. 

The Ministry of Health’s (MOH) director of medical services Kenneth Mak said on Thursday that most of the pre-school staff who tested positive are not infectious, as these were not active infections but old ones. The majority were also asymptomatic cases.

READ: More than 33,100 COVID-19 tests carried out on pre-school staff, positive cases no longer infectious: MOH

From May 18 to May 28, at least 27 out of 57 COVID-19 cases found in the community were asymptomatic. The cases found from active testing of pre-school staff are among them.

Infectious diseases expert Alex Cook said that he is “not too concerned” about the newly detected asymptomatic infections, since it was known that a fraction of infections are asymptomatic from quite early in the pandemic.

“While the number seems very surprising at first, especially if you scale it up to the whole population, it’s less worrying than (it) initially appears. We’ve known that there is probably undiagnosed infections, but these findings start to shed light on how much there has been so far,” said the vice-dean of research from the Saw Swee Hock School of Public Health at the National University of Singapore.

Professor Cook added: “We can’t stop asymptomatic cases per se, but we can try to stop them from contributing to the epidemic, by doing sweeps just like this one. Mass testing has been one of the cornerstones of Korea’s success in bringing their epidemic under control.”

READ: COVID-19 patients who still test positive but clinically well by day 21 of illness can be discharged


Case details published by MOH also show that, of the cases since May 18, about 10 people went to work despite onset of symptoms. Among them are a 58-year-old woman who went to work at Bishan MRT station, three women who work at various pre-schools and a few who were on duty at worker dormitories – where the majority of the coronavirus infections are now centred.

Data from studies have suggested about 80 per cent of COVID-19 patients will experience mild symptoms and remain relatively well, about 15 per cent will develop more severe disease, mainly pneumonia, and about 5 per cent of those infected may require critical care.

For those with mild symptoms, it can be just a mild fever which goes away after the first two days of illness, according to an ongoing study by the National Centre of Infectious Diseases (NCID) and the Saw Swee Hock School of Public Health.

The qualitative study, which started from March, examines COVID-19 patients’ experiences through in-depth interviews. One of the preliminary findings from the study was that many patients initially had mild and non-specific symptoms, so it was hard for them to decide to seek medical care.

READ: Singapore reports 611 new COVID-19 cases, including 3 Singaporeans or permanent residents

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“Because the symptoms were very mild, some of the interviewees just did not suspect this was COVID-19,” said Dr Mark Chen, NCID’s head of research, in response to media queries about why some patients may have gone to work despite the onset of symptoms. “But there could also be other reasons, and we are working with our partners to understand this issue better.”

This is one of the reasons the virus is so hard to control, said Professor Cook.

“The symptoms for many cases, and probably for most cases early in the infection, are quite ‘generic’: They may resemble the kinds of colds that we routinely shrug off,” he said. 

“The pre-school staff, in particular, are probably exposed to so many bugs through their work that it would be natural for them or their GP (general practitioner) not to have suspected this was COVID-19. 

“I hope with the increase in testing capacity we can test all cases with any suspect symptoms arriving in primary care, as that should help cut transmission substantially.”

Singapore has swab tested 218,996 people as of May 25, equivalent to about 38,400 people tested per million of its population.

READ: COVID-19: Phase 2 of post-circuit breaker reopening could begin before end-June, says Lawrence Wong


Since the start of the outbreak, MOH has advised people to consult a doctor if they have fever, cough and other flu-like symptoms. They are to be issued five days of medical leave and are required to stay at home for the duration.

Authorities have also provided an online symptom checker which helps the public determine if they are at risk. Among the symptoms on its checklist – difficulty breathing, cough, a fever of above 37.5 degrees Celsius, sore throat, diarrhea, a runny nose and loss of taste or smell. Many of these are not specific to COVID-19.

While the loss of taste and smell, or anosmia, is relatively specific for COVID-19, it is present in less than half of all COVID-19 patients, NCID said. A number of people with mild symptoms have reportedly tested positive for the disease after noticing this particular symptom.

READ: COVID-19: Retailers struggle amid uncertainties about reopening, recovery of sales

For non-specific symptoms, such as sore throats, it’s harder to tell. 

“I would say, if by the next day things don’t get better, or if additional symptoms develop, then it is a signal that one should see a doctor and be properly evaluated,” said Dr Chen.

This is particularly if there are other factors that may increase the risk of catching COVID-19. Dr Chen pointed out that MOH is now updating the public daily on some places that COVID-19 patients visited. 

READ: FairPrice supermarkets at Hillion Mall, Bukit Panjang Plaza among places visited by COVID-19 cases while infectious

“Those that visited these places need to be extra vigilant if symptoms develop. Because even if we scale up our capacity to test for COVID-19, which the Ministry of Health has already done, to get tested, you have to go seek help in the first place,” he said.

“If you have symptoms, then go to Public Health Preparedness Clinic or polyclinic, and let the doctors there assess you accordingly.”

Professor Cook also noted that with increased testing, authorities will find more COVID-19 cases.

“This could cause the numbers of diagnosed cases to rise. However, it’s better to have sweeps than no sweeps, so perversely a rise in the total number of cases may actually be a good thing in terms of the control of the epidemic,” he said.

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Source: CNA/hm(nc)


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