Sensitivity of SARS-CoV-2 RNA polymerase chain reaction using a clinical and radiological reference standard.

OBJECTIVES: Diagnostic tests for SARS-CoV-2 are important for epidemiology, clinical management, and infection control. Limitations of oro-nasopharyngeal real-time PCR sensitivity have been described based on comparisons of single tests with repeated sampling. We assessed SARS-CoV-2 PCR clinical sensitivity using a clinical and radiological reference standard. METHODS: Between March-May 2020, 2060 patients underwent thoracic imaging and SARS-CoV-2 PCR testing. Imaging was independently double- or triple-reported (if discordance) by blinded radiologists according to radiological criteria for COVID-19. We excluded asymptomatic patients and those with alternative diagnoses that could explain imaging findings. Associations with PCR-positivity were assessed with binomial logistic regression. RESULTS: 901 patients had possible/probable imaging features and clinical symptoms of COVID-19 and 429 patients met the clinical and radiological reference case definition. SARS-CoV-2 PCR sensitivity was 68% (95% confidence interval 64-73), was highest 7-8 days after symptom onset (78% (68-88)) and was lower among current smokers (adjusted odds ratio 0.23 (0.12-0.42) p < 0.001). CONCLUSIONS: In patients with clinical and imaging features of COVID-19, PCR test sensitivity was 68%, and was lower among smokers; a finding that could explain observations of lower disease incidence and that warrants further validation. PCR tests should be interpreted considering imaging, symptom duration and smoking status.

Colorectal cancer mimics: a review of the usual suspects with pathology correlation.

Colorectal cancer is the third most commonly diagnosed cancer in men and second most commonly diagnosed cancer in women worldwide. Initial diagnosis of colorectal malignancy is generally made on colonoscopy, sigmoidoscopy or digital rectal examination; however, with increased use of CT as primary investigation in patients with lower gastrointestinal symptoms, the diagnosis of colon cancer is often first apparent to a radiologist prior to more invasive tests. CT can demonstrate a discrete soft-tissue mass that narrows the colonic lumen or focal nodular wall thickening/stricture and a variety of pericolonic changes. Pattern of wall thickening has been described as an aid to differential diagnosis; however, significant overlap remains between primary colonic tumor and non-colonic tumors or benign conditions. Imaging is non-specific, and appropriate clinical history, direct inspection, histological analysis, and sometimes discussion at MDT are essential for accurate diagnosis and treatment planning. In this article, we will review the imaging features of some of these benign and malignant mimics of colorectal cancer, with accompanying histology slides where appropriate.