Why the White House is highlighting virus 'positivity rates'
S E E D E D C O N T E N T
A key metric is cropping up more and more at the coronavirus task force briefings.
White House response coordinator Deborah Birx on Wednesday and Thursday highlighted what she called the positive rate of coronavirus tests, a figure that helps measure the severity of the outbreak in different parts of the country.
Why is this measure important? While much attention has been placed on the number of tests being conducted, the proportion of tests that come back positive can offer both a broader and more detailed view of the pandemic.
“Epidemiology is a bit like baseball,” two public health experts, Farzad Mostashari and Ezekiel Emanuel, recently wrote in the news publication Stat . “Knowing that a ball player has gotten 134 hits isn’t that informative. What is informative is knowing that those 134 hits were made during 335 at-bats, which translates into a batting average of .400.”
Knowing how that percentage of positive tests is changing can help determine the course of the outbreak, they wrote.
Birx used the measure Wednesday, along with the number of new cases per day, to contrast the severity of the outbreak in two of the biggest U.S. cities.
New York had a positivity rate of more than 40 percent, with 11,000 new cases per day. In contrast, Los Angeles, which along with much of the West Coast is seen as a relative success story, had a positivity rate of just 9 percent and 800 new cases.
“And so this really gives us some idea of what it takes,” Birx said, pointing to Los Angeles. “They have been continuously mitigating.”
Areas at risk of becoming the next epicenter had positivity rates between those of New York and Los Angeles, effectively serving as a warning sign. New Orleans had a positivity rate of 28 percent, followed by Detroit at 26 percent and Chicago at 18 percent.
The metric can also be read as an indicator that the country is not doing enough testing.
Nationally, the positivity rate of coronavirus tests is about 20 percent. Ashish Jha, director of the Harvard Global Health Institute, said that is “absolutely” a sign of insufficient testing.
He also noted that the positivity rate has increased in the past two weeks, an indication that the U.S. is not ramping up its total number of tests fast enough to keep pace with the spreading virus.
“A very high percent positive rate means you're probably missing a lot of people who have the disease,” he said, suggesting New York may have even more unconfirmed cases.
But in places such as Los Angeles, where the rate is much lower, that is a sign “there probably aren’t a lot of cases that I’m not seeing.”
Los Angeles County on Friday extended its stay-at-home order to May 15. It was previously scheduled to end on April 19.
The positivity rate certainly has its limits as a metric, though, mainly because it depends in large part on who is getting tested.
The bulk of testing is not being carried out in a systematic or randomized way that would best answer questions such as how far the virus has spread in a community.
“It can be so strongly influenced by just exactly what are the criteria for testing,” said Jeffrey Martin, a professor of epidemiology and biostatistics at the University of California San Francisco.
He said better metrics for the severity of an outbreak are deaths and intensive care unit admissions.
To help improve the reliability of the positivity rate, Mostashari, a co-author of the Stat article, called for comparing test results from a “consistent setting,” such as the emergency room, as a more standardized metric than the current “haphazard” testing analysis.
Mostashari, CEO of the health care company Aledade and a former New York health official, called for “testing consistently in those places apples to apples and then [comparing the] positivity rate.”
He said the U.S. Department of Health and Human Services should put forward clearer requirements for labs to report details of their results to aid in that effort.
A clear picture of how many people in a community, even those who did not have symptoms, have had the virus likely will not come until a different kind of testing takes hold: blood tests known as serology tests. Those can determine if people have ever had the coronavirus, to measure the prevalence of the virus in a community.
“What we really are all waiting for is seroprevalence,” said Donald Thea, a professor of global health at Boston University.
Birx made a similar point at the White House on Friday by pointing to data that could come from a finger-prick blood test being developed.
“That’s a question we still have,” she said. “Is this the tip of the iceberg, or is this half the iceberg or three-quarters of the iceberg, what we have seen to date?”
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"To help improve the reliability of the positivity rate, Mostashari, a co-author of the Stat article, called for comparing test results from a “consistent setting,” such as the emergency room, as a more standardized metric than the current “haphazard” testing analysis."
The only thing 'the white house' is highlighting are Trump's ratings compared to certain TV programs.
We're not going to be able to responsibly talk about opening up society again without some kind of testing we can trust.
There currently is no "testing" occurring at rates that can provide any details to the spread of the virus.
Horrifying statistics were confirmed Thursday, that the United States has over 450,000 cases of coronavirus and still under 1 percent of the population has been tested.
The available test only determines the presence of an active infection. Increasing the number of negative test results doesn't provide actionable information. An individual can test negative one week and positive the next. A negative test result doesn't mean the individual has dodged a bullet; the test doesn't impart any protection against infection. For an accurate understanding of the progression of the pandemic, those with negative test results will need to be repeatedly tested.
Testing everyone in the United States only provides a snapshot for a brief period of time. It would be necessary to test everyone on a regular schedule to observe trends in the spread of infection. The currently available test is not suitable for epidemiological modelling.
The metric of immediate importance are the number of hospitalizations, the number of ICU admissions, and the number of fatalities. That's where the pandemic is being fought at present. The number of positive test results may provide an indication for future need for medical treatment. But negative test results will not provide actionable information.
The continuing demand for testing is motivated more by economic concerns than health concerns. The testing results are being utilized to justify lifting social distancing requirements and reopening the economy. But the currently available test is inadequate for that purpose. What is needed is a test for immunity. Those who have developed immunity can return to some level of normalcy. Those who have not developed immunity will need to continue with precautions to avoid infection.
A return to normal will depend upon immunity; not on presence or absence of active infection. That's the reason development of vaccines is being fast tracked.
The economic concerns are not trivial. Inventories are being depleted. Things break and wear out, needing replacement or repair. The available stockpiles of food, medications, cleaning supplies, and consumable items are being depleted and need restocking on a continuing basis. The threat of natural disasters has not changed. Some segments of the economy have continued operating throughout the pandemic. But the need for social distancing has impeded normal operation. The fundamental or essential economy has been hampered but has not completely shut down.
Exactly. There was concern yesterday for a number of recovered LA patients released weeks ago who have tested positive again while showing no symptoms.
Fear not, the China travel ban does not apply to trade. FedEx flights from Beijing land daily in LA & SF. Every port in California is busy unloading Chinese ships, manned by Chinese sailors, filled with all manner of Chinese made products from toys to medicines.
A potentially steady supply of virus.
Not surprising since China is the factory that allows us to pat our backs for strides in environmental wokeness. China has not offered any sort of philanthropic assistance, either. How else can distributors in the United States engage in profiteering?
US manufacturing, through Herculean efforts, have increased production of N95 masks to 39 million a week. Of course, not all those masks are available for use in the United States since that increased output supplies the North and South American continents.
Not to worry. President Joe will lead a renaissance in US manufacturing. We'll be ready next time.
Oh come on Nerm...3M was ready.
Yes, 3M was ready and did not wait to double production. But doubling production was not adequate for the level of need.
The United States needed more manufacturing capacity than 3M could provide. And don't overlook that 3M having to compete with foreign manufacturers during normal times has contributed to inability to supply need.
The need increased much more than 3M could supply because the competing foreign supply chain collapsed. That's not 3M's fault; that's the fault of allowing dependence on foreign supply chains.