The test was developed by researchers in the U.K. and delivers results to doctors in hours, allowing them to tailor treatment to patients for the best potential outcome. The test is now being rolled out at Cambridge University Hospitals.
For the study, researchers analyzed data from 81 patients with COVID-19 and 144 patients without the virus who received mechanical ventilation between March 15 and August 30, 2020. The researchers found that patients with COVID-19 were “significantly more likely” to develop ventilator-associated pneumonia—a lung infection that develops in someone who is on a ventilator—than those who did not have COVID-19. The scientists also found that select pathogens were more likely to cause pneumonia. The results of the research were published this month in the journal Critical Care.
As a result, the test—which has been dubbed the Cambridge test—was born.
How Pneumonia Is Typically Diagnosed
Typically, a pneumonia diagnosis takes time. Bacterial samples must be taken from a patient and grown in a lab, which can take 48 to 72 hours to get results, study co-author Andrew Conway Morris, PhD, an intensive care consultant and Wellcome Trust Clinical Research Career Development Fellow at the University of Cambridge, tells Verywell.
“These are slow, and often the bacteria don’t grow, either because the culture conditions are not optimal for that specific bacteria or because the patient has already received antibiotics which prevent bacterial growth,” he says. “As a result, the results of standard cultures are hard to use clinically, and patients are often started on broad-spectrum antibiotics.”
Morris says doctors need to identify the specific bacteria that is causing pneumonia in order to better target and treat it. It’s a “major problem” when they can’t, he says.
“In patients in intensive care, it is possible to have a clinical picture which looks like pneumonia, but isn’t—and these ‘pneumonia mimics’ do not respond to antibiotics,” Morris says.
Patients who are on ventilators in the ICU—especially those who have COVID-19—have inflamed lungs, Morris says. “This shows up on chest X-rays, as well as the patients having fever and raised white blood cell counts,” he explains, noting that these are typically signs of pneumonia. But, Morris points out, “COVID-19 is caused by a virus, which does not respond to antibiotics.”
“Whilst we found that COVID-19 patients were much more susceptible to secondary pneumonia—pneumonia that develops in the ICU—knowing when patients had developed this secondary pneumonia is difficult because COVID-19 can look like a bacterial infection,” Morris says. “The only reliable way to differentiate these things is to test for bacteria. Our existing culture-based tests are slow and insensitive.”
The Cambridge Test
The Cambridge test detects the DNA of up to 52 different pathogens, allowing for faster and more accurate testing. The test specifically uses multiple polymerase chain reaction (PCR) to detect the DNA of the bacteria, fungi, or virus. It can also test for antibiotic resistance. Doctors can get results in about four hours.
“The idea of this test was to give us faster, more accurate results which could lead to rapid evidence to guide treatment, allowing us to select the correct antibiotic if bacteria were found but also to hold off giving antibiotics if there were no bacteria there,” Morris says.
The concern and part of the reason for this test, he says, is antibiotic resistance. “Antibiotic resistance is a major problem in ICU, and some of our antibiotics come with toxic side effects,” Morris says. “It is best if they are only used when strictly necessary.”
Morris says he and his team made sure the test “covered a range of bugs that can cause lung infection, including viruses, fungi, and bacteria.”
He’s hopeful that the research will help more patients in the future. “I hope that our study raises awareness of the problem of secondary pneumonia in COVID-19 patients treated in the ICU, and informs doctors about the antibiotic therapies which can be used,” Morris says. “I also hope that it brings greater awareness of the role of rapid diagnostics in the management of pneumonia in ICU, encouraging their uptake.”
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