- Coronavirus case totals in China, Italy, and the US could be at least 10 times higher than the reported figures.
- Many patients likely haven’t been identified due to limited testing capacity, testing errors, and difficulty tracing asymptomatic cases.
- Blood tests could eventually reveal how many people have recovered, but some deaths may never be counted.
- For the latest case total and death toll, see Business Insider’s live updates here or visit the homepage for more stories.
The world may never know the full extent of the coronavirus pandemic.
Researchers agree that the true number of COVID-19 cases is much larger than official global tally – particularly in nations with severe outbreaks like China, Italy, and the US.
In these countries, limited testing capacity and the difficulty of finding and identifying asymptomatic cases has likely caused many patients to go undiagnosed. COVID-19 tests can also produce false negatives if they aren’t administered properly or if a patient isn’t shedding enough virus to be detected in a sample.
Some public-health experts have suggested that the actual case totals in China, Italy, and the US could be at least 10 times higher than the current figures.
“Really nobody knows,” Elizabeth Halloran, a biostatistician at Fred Hutchinson Cancer Research Centre and University of Washington, told Business Insider. “A lot of people have been missed.”
National outbreaks could be much larger than data suggests
Halloran said the actual number of US cases could be anywhere from 5 to 20 times the current number, based on recent models. But any model, she added, should be taken with a grain of salt.
Many coronavirus models are based on back calculations that try to determine how many people were infected several weeks ago. Researchers then extrapolate these findings to estimate the present number of cases.
So far, these methods have indicated that China, Italy, and the US are all underreporting cases by a similar order of magnitude.
Neil Ferguson, a professor of epidemiology at Imperial College London, estimated in February that China had only detected around 10% or less of its coronavirus cases.
Similarly, the head of Italy’s Civil Protection Agency told the newspaper La Repubblica in March that it was “credible” to assume a ratio of one confirmed case for every 10 infections in Italy.
Trevor Bedford, an epidemiologist at Fred Hutchinson, estimated last weekend that the US was confirming between one in 10 and one in 20 infections. That would put the actual case count at around 5 million to 10 million.
A March study in the journal Science suggested that the US outbreak was five to 10 times larger than the reported number.
“A lot of the models take different methods and converge on the same results,” Halloran said, though she added that “there is a lot of uncertainty.”
Identifying asymptomatic patients would raise the case count
One of the biggest hurdles to getting accurate coronavirus case counts is the fact that infected people can be asymptomatic.
“We don’t know how many asymptomatic infections there are,” Halloran said. “Those people, we suspect, are a source of a lot of the transmission in the population.”
Anthony Fauci, director of the National Institute of Allergy and Infectious Disease, recently estimated that between 25% and 50% of people infected with the coronavirus may never show symptoms but can still be contagious.
Some estimates are even higher. A study of 3,000 people in Vo’Euganeo, a village in northern Italy, found that between 50% and 75% of coronavirus patients there were asymptomatic. In a letter to Italian authorities in Tuscany, Sergio Romagnani, a professor of clinical immunology at the University of Florence, said that asymptomatic patients represent a “formidable source of contagion.”
A February report from the World Health Organisation found that asymptomatic cases were “relatively rare” in China, but the country’s National Health Commission later determined that 78% of new infections reported on April 1 were asymptomatic. This suggests patterns from China’s early data may not be reliable or widely applicable.
Testing errors and limited testing capacity obscure the reality of the pandemic
The more tests get administered, the more countries are likely to identify cases. But many nations are still struggling to provide enough tests for prospective patients. Even in Italy, which has one-fifth the population of the US and 23 times fewer people than China, tests aren’t accessible to all residents.
At the height of China’s outbreak, the country also reserved tests for people who were sick enough to show up at a hospital. Since tests were initially in short supply and took days to process, Chinese doctors briefly resorted to diagnosing patients in the Hubei province via CT scans. Colin Furness, an infection control epidemiologist at the University of Toronto, told ProPublica that medics in China also started diagnosing patients based on symptoms alone.
In New York City, the epicentre of the US outbreak, hospitals are still limiting testing to patients with severe illnesses. States with major outbreaks like California and Washington have also reported a backlog in test processing and shortages of materials like swabs.
What’s more, tests can be faulty. A study of more than 1,000 hospital patients in Wuhan, China, found that 75% of people whose tests came back negative likely had COVID-19 based on their CT scans.
“There are a lot of things that impact whether or not the test actually picks up the virus,” Priya Sampathkumar, an infectious-diseases specialist at the Mayo Clinic, told AFP. “It depends on how much virus the person is shedding (through sneezing, coughing and other bodily functions), how the test was collected, and whether it was done appropriately by someone used to collecting these swabs, and then how long it sat in transport.”
Together, these limitations contribute to a vast underreporting of cases.
Tests for current patients “need to be faster and cheaper and more reliable and available in much greater quantities,” Halloran said.
Blood tests could identify more cases, but some deaths will never be counted
Public-health experts are still debating the death toll of the 1918 Spanish flu more than a century later. Some estimate that around 20 million people perished, while others believe the death count reached 100 million.
Halloran said the current pandemic will be easier to understand, since researchers will eventually be able to use a blood test to determine whether people have developed antibodies to the virus.
“We’ll have to piece it together with serology afterwards,” she said. “There could be a lot more people infected than we thought.”
But antibody testing would have to be rolled out on a giant scale to give researchers a firm understanding of the scope of the pandemic.
“You could go around and test people that are going back to work or go out in the neighbourhood or look at healthcare workers – how many of them actually had the infection and never knew it,” Halloran said. “That’s what we need to do to understand how widely people have been infected.”
Even then, she added, there will always be some cases that are never identified.
Between March 4 and April 4, New York City reported more than twice the typical number of monthly deaths, according to the New York Times. Of the 5,330 excess deaths recorded during that month, only 3,350 were confirmed coronavirus deaths.
“We won’t ever know if those 2,000 deaths were coronavirus deaths or from something else,” Halloran said. “It’s a single city in a single month where they probably have a two-week delay in reporting deaths. Probably the number is much greater.”