The swab’s weakness is low sensitivity. Only about 50-80% of those with Covid-19 infection will be identified by the RT-PCR test. In other words, it misses up to half of people with the disease.
CT scans found the disease more than swab testing did: in many studies, including china’s medical data.
China reported that chest CT found 97% of Covid-19 infections. Also, found that 48% of patients who had negative results on the swab test, which detect the coronavirus’s genome, in fact had the disease.
In China, while the swab was routinely missing cases of Covid, a CT scan often found it.
CT scanning is far safer for health care workers than the swabs that reach the throat via the nose, and often trigger explosive coughing that can spew virus particles into the air.
Radiologists have watched the coronavirus disease 2019 (COVID-19) pandemic unfold, wondering if and how imaging could be useful for diagnosis. Perhaps imaging could aid in screening or accelerate the speed of diagnosis, especially with shortages of RT-PCR. The current swab tests for the novel coronavirus are missing up to 30% of infected people. CT Scans, were widely used in China to identify cases, and their reliability there is fueling growing interest in adding chest CT to the diagnostic arsenal in the U.S.
Covid-19. In one recent study of 1,014 patients, published in the journal Radiology , scientists in China reported that chest CT found 97% of Covid-19 infections. In comparison, the study found that 48% of patients who had negative results on the swab test, which detect the coronavirus’s genome, in fact had the disease.
“Once you’re a couple of days into infection, chest CT scans don’t miss,” said an emergency medicine physician in Louisiana who asked not to named. With the swab test missing 30% to 50% of cases, physicians in China called for the diagnostic use of CT early in the outbreak there, and “fever clinics” set up in Wuhan and elsewhere began routinely using them.
The alarming rate of false negatives from molecular testing, as well as the often days long wait to receive results, is driving more and more medical centers to adopt CT scans for Covid-19 testing. They include Mount Sinai in New York City, Bloomberg reported, and a growing number of physicians across the country.
Last week the Fleischner Society, an international group of chest radiologists, broke with the CDC and the American College of Radiology, which recommend against chest CT to diagnose Covid-19. The Society concluded that it can in fact be appropriate in some situations, including a pandemic.
“Every ER physician I know recognizes the power of these scans,” said Joseph Fraiman, an emergency medicine physician at hospitals in the New Orleans area who does two or three chest CTs on suspected Covid-19 patients every shift. “Aggressive disease identification would involve both [swab tests] and CT to ensure the highest sensitivity, missing the fewest cases possible.”
But despite China’s experience, the use of chest CT to diagnose Covid-19 in the U.S. remains very limited (no one has data on how many have been done). That’s due in large part of the CDC and the American College of Radiology recommendations.
Some radiology literature suggests a pivotal role for CT. Ai and colleagues 1, report on 1014 patients who received both RT-PCR and CT in Wuhan, China, during their epidemic. They found that 97% of cases with RT-PCR-confirmed diagnoses had CT findings of pneumonia, and conclude, “CT imaging has high sensitivity for diagnosis of COVID-19”.
While the swab was routinely missing cases of Covid, a CT scan often found it.
In China, while the swab was routinely missing cases of Covid, a CT scan often found it. In other words, CT scans are more sensitive than the swab. Signature findings like ‘ground glass opacities’, for instance, accurately detected Covid-19. Were there false positives? Yes, because other lung ailments also show such findings.Better yet, CT scans offer an immediate answer, typically in a time window of peaking signs and symptoms—i.e. when the patient is most likely to be spreading the disease. Identifying infections five days earlier could save countless lives by ensuring timely isolation and treatment.
One of their objections is that CT scanners will become contaminated with the coronavirus. China, whose fever clinics routinely scanned 200 patients per day per machine, managed to clean the machines between patients well enough to avoid infecting health care workers or subsequent patients, however. Researchers there reported last month that CT scanning is far safer for health care workers than the swabs that reach the throat via the nose, and often trigger explosive coughing that can spew virus particles into the air. Thanks to staff training and between-patient scanner cleaning, after 3,340 CT scans for suspected Covid-19, another group of physicians in China reported, “none of the staff of the radiology department was infected with Covid-19.”
- 1.Ai T Yang Z Hou H et al.Correlation of chest CT and RT-PCR testing in coronavirus disease 2019 (COVID-19) in China: a report of 1014 cases.
Radiology. 2020; (published online Feb 26.) DOI:10.1148/radiol.2020200642
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