Low-dose chest computed tomography (CT) has been an effective screening tool for COVID-19, writes Amir Davarpanah, outlining a novel screening and triage strategy successfully used in Iran to diagnose patients. “This strategy was valuable at the peak of the outbreak in Iran,” he says, “and added a new angle to the important role of radiologists and teleconsultation during a global health crisis”.
Healthcare systems across the world are facing a sudden surge in COVID-19 cases and thoracic radiologists are on the front-line of diagnosis in countries with limited supply of polymerase chain reaction (PCR) testing kits for definitive diagnosis. Due to the nature of the emergency in Iran at the peak of the outbreak and the reported low sensitivity and short supply of PCR testing, we temporarily used chest CT criteria of COVID-19 pneumonia as a surrogate for PCR testing. In our case study, published in the Journal of the American College of Radiology, we described the implementation of a novel triage strategy using humanitarian teleradiology service for the screening of symptomatic patients. The patients with early clinical and laboratory findings suspicious for COVID-19 underwent low-dose chest CT and categorised into two groups according to presence or absence of imaging features of viral lung infection.
Aiming to address the shortage of subspecialty-trained thoracic radiologists in Iran, we created a smartphone-based solution using a social media platform, WhatsApp, to provide expert interpretation of CT scans. Our goal was the early identification and isolation of infected patients to minimise disease transmission. Patients with CT finings suggestive of viral pneumonia were followed by PCR testing for confirmation and were isolated. Patients testing positive were transferred to designated hospitals. Patients with findings inconsistent with viral pneumonia on chest CT were treated according to alternative diagnosis and followed clinically.
Since radiographic findings of COVID-19 infection on chest CT are nonspecific and largely overlap with other viral infections, implementation of screening chest CT will result in a higher number of false-positive cases compared to PCR testing. Nonetheless, CT could be a valuable screening tool due to higher sensitivity, specifically in epidemic areas where there is a high pretest probability for disease. In addition, our priority was to identify the majority of suspicious cases and to use PCR testing in a more selective fashion to minimise resource drain.
Other important issues to consider are the cost and availability of CT scanners, the availability of thoracic radiology expertise, and the fact that at the time of crisis, referrals to major hospitals should be limited to decrease risk of exposure in the healthcare setting. A potential solution is using outpatient imaging centers and teleradiology, which eliminates the need to send patients to overpopulated hospitals and provides near-real time consultation from experts located around the world.
There are other certain downsides for using chest CT for triage, one of which is radiation exposure. We used low dose chest CT, which uses about 25–30% of regular chest CT dose, to minimise radiation exposure. Another concern for imaging centres is the possibility of becoming the new COVID-19 hot spots. In order to address this concern and limit the exposure of healthcare workers, employees, and patients, deep cleaning and disinfection of the room and scanner was performed after each patient, and staff wore personal protective equipment when handling these patients. The downside is the delay generated by the prolonged closure of CT scanning equipment for deep cleaning.
In spite of these limitations, this strategy has been valuable at the time of the outbreak in Iran, and has added a new angle to the important role of radiologists and teleconsultation during a global health crisis. The decision to implement a similar CT screening programme depends on the prevalence of infection in any given country or region, the availability of PCR testing, and the availability of CT scanners. Performing a cost-effectiveness analysis by regional healthcare authority is crucial before making the decision to use chest CT as a screening tool for COVID-19.
Amir H Davarpanah is an abdominal and cardiothoracic radiologist working in the Department of Radiology and Imaging Sciences at the Emory University School of Medicine, Atlanta, USA.