core can accurately stratify patients with pneumonia in different COVID-19 risk categories.
Although this model has been shown to be a useful risk assessment tool for COVID-19 pneumonia, it may miss-label some patients. Indeed, forty-one (33.6%) patients of the negative COVID-19 subgroup presented a PSIC score ≥ 10, but the meaning of these findings may be somewhat misleading considering the sensitivity of the rRT-PCR test.
Furthermore, the PSIC score was proposed with no description of the methods used for the determination of score variables, grade scoring system and score cut-off, probably due to the need of fast interventions in the setting of a public health emergency.
This study presented several limitations. First, it was a retrospective analysis. Secondly, it included a limited number of patients reflecting the reality of a single-center department. Not all patients admitted to the ward were included in the validation cohort. Most patients were excluded due to lack of chest CT images since not all were considered to present criteria for the performance of a CT-scan when the clinical picture and the chest radiography were sufficiently informative and the CT radiation risks and costs were considered to outcome its benefits. Other patients were excluded due to a lack of information on other variables such as PCT and urinary antigen tests. However, it should be noted that the study was developed during the initial phase of COVID-19 in Portugal when diagnostic protocols were still being implemented and the exams were requested according to clinical presentation. Results in this study rely on the SARS-CoV-2 rRT-PCR test for the confirmation of positive COVID-19 cases. However, this test presents a sensitivity of approximately 66% - 80%  , which means that a considerable number of positive cases may have not been identified. Moreover, collected samples for the SARS-CoV-2 test were from Naso and oropharyngeal swabs, which present a lower diagnostic yield compared to lower airway samples . The authors hypothesized whether some of these patients could have been good candidates for the serologic monitoring during the acute phase and follow-up, particularly the ones with typical CT features. Regardless of the limitations, this is an attempt to validate a useful tool in the clinical practice with encouraging results, particularly when allocating patients at admission.
In this study, the PSIC score was a reliable and valid tool for assessing the probability of a positive SARS-CoV-2 rt-PCR test in inpatients with pneumonia. Findings suggest that slight adjustments of the PSIC score might be considered in this subpopulation. When dealing with a highly contagious respiratory virus, the use of diagnostic clinical risk scores coupled with laboratory tests at admission may facilitate hospital patient allocation while under observation promoting intra-hospital infection control. To validate the proposed risk score at a broader level and to improve it, it should be applied at a multicentric scale. So far, proposed models are poorly reported and at high risk of bias. Hence, they cannot be recommended in current practice.
VC conceptualized the study. AA collected and organized the data. FD, VD, AA and DN performed the statistical analysis. AA, DN, VD and VC wrote the manuscript. All authors reviewed the manuscript.
We would like to thank all the medical team that provided care to the patients admitted to the COVID dedicated department of Centro Hospitalar de Setúbal E.P.E.. We also would like to thank Ivone Fernandes M.D. whose hard work contributed to the continuous care of other respiratory patients while the team was divided.
 Wynants, L., Calster, V.B., Collins, B., Riley, R.D., Heinze, G., Schuit, E., et al. (2020) Prediction Models for Diagnosis and Prognosis of COVID-19: Systematic Review and Critical Appraisal. BMJ, 369, m1328.
 Woloshin, S., Patel, N. and Kesselheim, A.S. (2020) False Negative Tests for SARS-CoV-2 Infection—Challenges and Implications. The New England Journal of Medicine, 383, e38.
 SPCI (2020) Recomendaèões da