249 Low-dose-CT versus X-ray in patients with pneumonia Discussion In this study of patients clinically suspected of CAP at ED presentation, we found no benefit in using ULDCT as first line diagnostic procedure compared to using CXR regarding the proportion of patients diagnosed with CAP. Both at discharge from the ED, as well as after reviewing all available clinical data at day 28, the number of patients with a CAP diagnosis was not significantly different between groups. This refuted our hypothesis that the higher diagnostic accuracy of ULDCT leads to a higher number of patients diagnosed with CAP. In line with this finding, we also did not observe differences in antibiotic consumption or clinical outcome measures, such as hospital admission, length of hospital stay, mortality and functional health after 28 days. Claessens et al. assessed whether early multidetector chest CT scan affects diagnosis of patients visiting the ED with suspected CAP, and found it alters antibiotic management [3]. However, Claessens et al. used slightly different criteria to define clinically suspected CAP. Second, we report on a more heterogenous population, as represented by proportion definite CAP in both cohorts (51% vs. 33%)[3]. In a study on pneumonia in elderly patients, the probability of pneumonia was assessed before and after a low-dose CT (LDCT) scan and subsequently compared to the reference diagnosis made by an adjudication committee [11]. LDCT modified the estimated probability of pneumonia in 45% of patients. Correct reclassification was mainly observed in patients not having pneumonia according to the adjudication committee, suggesting that the potential benefit of the LDCT would mainly lie in reducing overdiagnosis of pneumonia [11]. In the OPTIMACT trial we reported a higher number of patients with CAP in the ULDCT group. In an exploratory analysis we only found a higher number of CAP patients in the ULDCT group among those with signs and symptoms of an acute respiratory infection but a temperature between 36°C and 38°C. Apparently, the higher proportion of CAP patients in the ULDCT group versus the CXR group in the OPTIMACT trial was mainly driven by a higher number of CAP patients in the afebrile subset of patients. This can be considered an interesting finding, since this is the group more likely to receive unnecessary antibiotics, and the increased sensitivity of ULDCT could help rule out disease more effectively. Based on data from literature and results presented in the present study, one could argue that the value of ULDCT seems most pronounced amongst those patients whose clinical presentation is not straightforward, such as elderly patients or afebrile patients. It should be subject of further studies to identify which groups of patients would benefit most from standard ULDCT imaging. Our analysis has limitations. First, even when ULDCT would not lead to more CAP diagnoses as compared to CXR, it could still lead to more accurate CAP diagnoses. Studies in which both CT and CXR were performed in one patient showed that the probability of pneumonia increased in some patients and decreased in others [3, 11]. Second, the COVID-19 pandemic may have changed the incidence, presentation and management of patients suspected of CAP, which is not accounted for in our study. Third, despite the fact that this was a representative cross-section sample of the emergency department population of two large Dutch hospitals, the results of this study cannot be translated directly to specific subgroups, such as the very old. 10
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