Asymptomatic transmission, under-detection and the speed of the COVID-19 pandemic's progress, swamping health systems at times, has made accurate data collection difficult, writes MedicalBrief.
An upward revision in China's COVID-19 death toll was "an attempt to leave no case undocumented" after medical services in the country's epicentre Wuhan were overwhelmed at the start of the outbreak, CGTN reports the World Health Organisation (WHO) said.
The total number of confirmed COVID-19 cases in central China's Wuhan as of the end of 16 April was revised up by 325 to 50,333, and the number of fatalities increased by 1,290 to 3,869. Local authorities said the revision ensures that the information on the city's COVID-19 epidemic is open and transparent.
Maria van Kerkhove, a WHO epidemiologist who took part in an international mission to China in February, said of China's revised figures: "This was done in attempt to leave no case undocumented."
The report says the Chinese authorities had gone back over data from funeral services, care homes, fever clinics, hospitals and detention centres, and patients who had died at home, in Wuhan, Hubei Province where the outbreak began late last year, van Kerkhove, the WHO's COVID-19 technical lead, told a virtual press conference in Geneva.
"What they have reported is that the discrepancies in these cases were due to a number of factors. First is that the healthcare system in Wuhan was overwhelmed at one point. And some patients died at home," she said. "Secondly is that medical staff were delayed in reporting of these cases because they were focused on providing care for those patients and they didn't fill out the forms in time," she added.
Mild cases were treated in temporary hospitals in Wuhan stadiums or other facilities, van Kerkhove said, adding: "In those situations the reporting wasn't done in a timely manner and so those cases were added." It was important to know the number of people who had died from the disease and to have "accurate reporting," which can be a challenge during an outbreak, she said.
According to the report, WHO experts believe that other countries hit by the pandemic will need to review their figures as Wuhan did. "I would anticipate that many countries are going to be in a similar situation where they will have to go back and review records and look to see did we capture all of them," van Kerkhove said.
Michael Ryan, the WHO's emergencies director, added: "All countries will face this." But he urged nations to produce precise data as early as possible, "because that keeps us on top of what the impact is, and allows us to project forward in a much more accurate way."
Chinese Foreign Ministry spokesperson Zhao Lijian noted that this kind of revision to epidemic statistics is not a rare case as it is also practiced as by other countries around the world as an international normalcy.
Among 6,764 people who tested positive for infection without showing symptoms, only one fifth of them — 1,297 — have so far developed symptoms and been reclassified as confirmed cases, China National Health Commission spokesperson Mi Feng is quoted in a Bloomberg report as saying. Some 1,023 are still being monitored in medical quarantine to see if they develop symptoms. The rest – 4,444 – have been discharged from medical observation after recovering from the virus.
The report says the phenomenon of asymptomatic transmission is a puzzling feature of the virus that’s allowed the pandemic to spread wider and faster than previous outbreaks. Researchers are still struggling to understand asymptomatic cases: there’s a possibility that patients who appear to be symptom-free are actually just manifesting symptoms that doctors don’t yet know to look for.
For months, a fever and dry cough were understood to be the disease’s main markers, and it’s only recently emerged that a loss of smell and taste is also a sign of infection.
China has not disclosed the range of symptoms it looks for, the report says.
Until recently, the discussion in South Africa around under-detection of cases centred on those who may have slipped through the net and remained unknown – which is generally what is accepted did happen, according to one of the National Institute for Communicable Diseases' (NCID) top epidemiologists, Professor Cheryl Cohen.
But, says a News24 report, the studies are now showing early proof that another type of spreader, those who could be passing the virus on unknowingly – as they show no visible symptoms of the virus, or display symptoms not immediately associated with COVID-19 – are in fact contributing to the spread, confirming early assumptions by researchers. Cohen said a question mark hangs over the likelihood of these asymptomatic infections, which some studies believe could be as high as 70% of infections, transmitting the virus, which is likely much lower than severe cases.
"That is the great thing that is not really known, and it’s an important piece of information for us to understand how important the so-called under-detection is," she said. "There are two levels of under-detection. There is a level of under-detection where we understand we have symptomatic people who have fever and cough, they may be mild, they may be more severe, they may be in hospital, and we accept that we may not be catching and testing all of them," Cohen sad. That number could be as high as none or 10 for confirmed cases, some studies have shown.
"I would say that it is generally accepted that we are missing some of the cases, but it is very difficult to quantify to what degree that is. It is based on probabilities, it is likely that when we had that huge wave of importation from overseas, there would have been additional importations that would have gone undetected and once those importations spread to additional people, it would have been very hard to find them in the ocean of respiratory disease that we find ourselves in as we go into the winter season."
According to the report, Cohen said the second issue around under-detection was the issue of asymptomatic cases. "It is an emerging area of research, only in the last week or two a whole host of studies have started coming out, all pointing to the same thing, the same idea that there is likely a large pool of cases, I don’t know how large, but some people are saying that up to 70% of cases could be asymptomatic or mildly symptomatic," Cohen said.
"That’s something that is going to have to be considered by mathematical modellers in South Africa and around the world, but it’s quite new, the evidence for that has only come out quite recently and that will, I think, be the emerging story."
She said there was evidence that asymptomatic people can transmit COVID-19, but they would likely transmit at a lower rate than symptomatic cases. "The question then is how impactful are they on a population level? That’s the difficult part."
[link url="https://news.cgtn.com/news/2020-04-18/WHO-says-China-s-death-toll-revision-aimed-at-documenting-all-cases–PMANqijEo8/index.html"]Full CGTN report[/link]
[link url="https://www.bloomberg.com/news/articles/2020-04-15/china-s-data-on-symptom-free-cases-reveals-most-never-get-sick"]Full Bloomberg report[/link]
[link url="http://www.china.com.cn/zhibo/content_75931802.htm#fullText"]Chinese Data[/link]
[link url="https://www.news24.com/SouthAfrica/News/studies-show-a-new-frontier-in-sas-battle-with-covid-19-spreaders-who-dont-know-they-are-infected-20200419"]Full News24 report[/link]