Polymerase chain reaction (PCR) testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is necessary for confirming a diagnosis of Coronavirus disease 2019 (COVID-19). Here we present a COVID-19 case of an elderly woman whose SARS-CoV-2 PCR tests showed false negative repeatedly by evaluating with different sampling sites and procedures. Nasopharyngeal swabs, suctioned sputum, and tongue swabs were collected for SARS-CoV-2-PCR. As for tongue swabs, we compared between two different sample conditions; one obtained with dry condition and the other obtained with moistened condition inside the oral cavity. SARS-CoV-2-PCR showed positive for an extended period with suctioned sputum samples compared with nasopharyngeal swabs and tongue swabs. No SARS-CoV-2 from a nasopharyngeal swab sample obtained on day 46 after symptoms onset was isolated despite high viral load (183740.5 copies/5μL). An adequate production of neutralizing antibody in a serum sample on day 46 was also confirmed. The number of RNA copies of the tongue swab samples was higher with moistened condition than with dry condition. The present case suggests that the difference of sampling site or sample condition can affect PCR results. High loads viral RNA detection does not always correlate with infectivity.
Case presentationA 63-year-old diabetic man presented with progressive red nodules on the anterior-lateral side of both legs (Figure 1) with worsening pain. C-reactive protein was elevated (3.81 mg/dL). Ddimer and venous ultrasonography were normal. The interferongamma release assay (IGRA) and tuberculin test were both positive without chest radiologic abnormalities.Histopathology of the nodules showed lobular inflammation with subcutaneous vasculitis (Figure 2A), and histiocyte and neutrophil infiltration with vascular destruction (Figure 2B-D). There were no caseating granulomas nor acid-fast bacilli, and Mycobacterium tuberculosis PCR was negative. The patient was diagnosed with erythema induratum of Bazin (EIB) and he underwent antituberculous therapy with a four-drug regimen for seven months without steroid use. He began to walk three weeks after treatment initiation and his erythema induratum resolved within two months.EIB is a rare subcutaneous granulomatous disease caused by an autoimmune reaction to M. tuberculosis (Mascaro and Baselga, 2008). It frequently occurs in the lower extremities and accompanies diabetes (Kara Polat et al., 2020). Its histology is
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