Locations and patients
This retrospective cohort study was performed in three hospitals affiliated to Babol University of Medical Sciences, including Rohani, Shahid Beheshti, and Yahyanejad hospitals, between February and March 2020. Babol was one of the first cities in north of Iran with confirmed cases. We initially included the individuals presenting with suspicious symptoms (fever, respiratory symptoms, such as cough, dyspnea, and sputum) who were referred to the emergency unit and underwent necessary clinical and paraclinical assessments for COVID-19. Chest CT scan was performed on all suspected individuals after triage. For RT-PCR testing, trained technicians collected nasopharyngeal swab specimens and sent them to the laboratories of Babol health center. RT-PCR was done for all triaged patients. The time gap between the nasopharyngeal swab sampling and CT scan was less than 12 h.
Patients with chest CT scans suggestive of COVID-19 and at least one of the following criteria were admitted to the hospitals, according to the national COVID-19 protocol: hypoxia (O2 saturation ≤ 92%), tachypnea (respiratory rate ≥ 22), tachycardia (pulse rate > 100), or hypotension (systolic blood pressure 100 mmHg or less). The following data were extracted from the patients’ medical records by a trained research team: demographic information (such as sex and age), comorbidities (such as cardiovascular diseases [CVDs], asthma, chronic obstructive pulmonary disease [COPD], and diabetes). Cases with incomplete information about comorbidities and/or RT-PCR results, as well as those declined to participate in the study, were excluded from further investigations. We categorized clinically the COVID-19 pneumonia into different disease severities (moderate, severe, critical) based on the definition by World Health Organization (WHO) . Patients with mild disease were not admitted as per the national COVID-19 protocol.
See more: Covid 19 ct scan
Imaging collection and analysis
The patients underwent non-enhanced 16-detector-row CT scan during deep inspiration breath-hold in the supine position (Siemens SOMATOM Emotion 16, Siemens Healthcare, Med Image Systems, Germany). The scanning parameters were as follows: tube voltage, 100 KV for patients with BMI ≤ 30 and 120 KV for patients with BMI > 30; tube current, 50-100 mAs; pitch, 0.8-1.5; thickness, 1-3mm; Matrix, 512. Additional image reconstructions were not necessary. The CT scans were evaluated by a single radiologist with an experience of more than 15 years (R.M.), who was blinded to the patients’ status. The following imaging characteristics were recorded: ground glass opacity, consolidation, reticular pattern, lesions distribution (peribronchovascular or peripheral), side of lung involvement, crazy paving, pleural effusion, number of lung zones involved, cavity, and tree-in-bud pattern.
The CT severity score (CSS) for each patient was calculated based on the percentage of lung zones involvement . In this regard, right and left lungs were divided into three (upper, middle, and lower) and two (upper and lower) zones, respectively. The scoring system was as follows: score 0 representing no involvement, score 1 representing < 5% involvement, score 2 representing 5-25% involvement, score 3 representing 26-50% involvement, score 4 representing 51-75% involvement, score 5 representing > 75% involvement. Finally, sum of the scores yielded the total CSS, ranging from 0 to 25.
The statistical analyses were performed by SPSS software. The obtained data initially underwent descriptive analyses. To assess normality of the data, Kolmogorov-Smirnov test was used. For comparing parametric and non-parametric continuous data between the groups, independent t test and Mann-Whitney test were used, respectively. We performed chi-squared test and logistic regression analysis to investigate the association of baseline information and imaging findings of the patients with study outcomes (COVID-19 status and adverse disease outcomes). The factors with significant association were entered into the multivariable analysis. The results were presented as odds ratio (OR) as well as 95% confidence interval (CI). We also calculated the area under the curve (AUC) to estimate the predictive ability of CT scan features for the study outcomes. A p value less than 0.05 was considered statistically significant.