Coronavirus: US death rate likely to fall as new rules allow for wider testing
- Rule change means independent laboratories will be able to use their own tests, making them available to less severe cases
- US fatality rate stands at about 4.5 per cent, compared with 3.9 per cent in mainland China
Testing for Sars-CoV-2, the clinical name for the virus, has expanded since the US government heeded a call from the American Society for Microbiology (ASM) for the US Food and Drug Administration (FDA) to lift “emergency use authorisation” restrictions that prevented clinical microbiology labs from using their own independently developed tests.
That change took effect on February 29, more than five weeks after the first US case was confirmed. Other public health protocols that had kept the denominator of confirmed cases in the US low – such as guidance that discouraged testing of anyone who had not travelled abroad to areas most affected by Covid-19 – have also been cleared.
With too few FDA-approved tests and screening criteria limited to individuals with particular travel histories or with more severe symptoms, US public health officials were testing a subset of cases more likely to progress towards death.
“When you test very widely, then your denominator becomes very large, so the case fatality rate will go down,” said Benhur Lee, Ward-Coleman chair in microbiology at the Icahn School of Medicine at Mount Sinai in New York.
The newly relaxed regulations will allow several diagnostics companies to start offering their own tests at medical practices and clinics in the US. For example, Quest Diagnostics said it would start making its tests available this week.
The United States reported 423 Covid-19 cases and 19 deaths as of Monday, according to the US Centres for Disease Control and Prevention (CDC), making the fatality rate 4.5 per cent. That compares with 3.9 per cent for mainland China, which has the world’s largest number of cases, 0.7 per cent for South Korea, and zero for Singapore, which has 160 cases.
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But only about 6,000 samples from suspected coronavirus patients in the US had been tested as of Saturday, FDA commissioner Stephen Hahn said in a press briefing.
“Up until very recently, there hadn’t been much testing for SARS-CoV-2 in the United States,” Stefano Bertuzzi, the ASM’s CEO, said in an announcement circulated to members on March 6 and posted on the organisation’s website on Monday. “In the past week, this has changed.”
“Experts warned that the small number of cases in the United States so far may be a reflection of limited testing – due to problems with the CDC diagnostic kits and the Food and Drug Administration regulations – not true spread of the virus,” Bertuzzi said.
“Clinical microbiologists sounded the alarm that we did not know the full extent of the virus in the United States, putting everyone at risk,” he added.
As of Sunday, 78 state and local public health labs in 50 states and Washington DC were currently using Covid-19 diagnostic tests, according to a CDC update on Monday.
“The lack of testing artificially inflates the death rate, because you’re only testing the most severe cases, so the denominator is small,” Lee said.
“In the US, if the test isn’t officially sanctioned or FDA certified, it was unclear whether you can report or act upon those numbers,” he said.
“This is very different from a place like Singapore, where there is one agency that takes control,” he added. “Here in the US, you have 50 different state public health authorities, and some of them are afraid” to report cases that were not confirmed through FDA-approved tests.
“By the day, they’re changing their criteria,” Lee said.
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Those changes include the CDC’s decision last month to end limitations on testing individuals who had recently travelled to China or had close contact with a confirmed case.
Costs for the tests vary in the US. Most people with health insurance policies will need to fork out a co-payment of US$10 to US$20 or pay a deductible.
The tests will be free for those living in the states of Washington and New York, where emergency orders aimed at containing Covid-19 prohibit insurers from charging co-payments or deductibles for testing.
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