Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) Rapid Antigen Detection Testing (RADT) has been subjected to several evaluations in reference to diagnostic accuracy, ranging from small scale up to large population studies including nation-wide community-based studies. All confirmed the diagnostic accuracy of the tests which were strongly dependent upon the infection's population prevalence. In our retrospective study, parallel SARS-CoV-2 Panbio™ RADT assay, including real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR) tests, were aimed to evaluate diagnostic performance regarding the rapid antigen diagnostic testing. Out of 4,440 paired tests, 609 samples tested positive using RT-qPCR, resulting in a prevalence of 13.7%. Panbio detected 251 (5.7%) positive tested samples. Overall sensitivity was 41.2% (95% CI 37.4–45.2%) and overall specificity was 99.7% (95% CI 99.4–99.8%). Positive predictive value (PPV) was 95.1% (95% CI 91.8–97.1%) and the negative predictive value (NPV) was 91.4% (95% CI 90.5–92.2%). RADT sensitivity increased with stratification in reference to the results according to PCR Cycle threshold (Ct) and presence of the symptoms considerably influenced PPV and NPV. Sensitivity in the group of Ct values ≤ 20 was 91.2%, 68.6% within the Ct range of 20–25, 47.9% in the group of Ct values between 25 and 30, and 12.6% in the group of Ct values between 30 and 35. A follow-up of the positive cases aligned with RT-qPCR testing and comparison of the general population enrolled in the testing in which the fatal cases occurred enabled us to estimate real clinical diagnostic performance regarding the SARS-CoV-2 Panbio RADT. Based upon our results, we recommend the SARS-CoV-2 Panbio RADT tests be carried out as the primary test, without parallel PCR testing, only among high population prevalence rates of the infection and to be used for symptomatic individuals with average or low severe disease developmental risk. In the case of high risk regarding the development of severe infection complications, a parallel SARS-CoV-2 RT-qPCR is needed to be carried out to attain proper diagnostic accuracy and avoid delaying appropriate medical care.

BackgroundSystemic sclerosis (SSc) is a systemic autoimmune disease leading to tissue atrophy, vascular damage and organ failures, and therefore causing severe disability. Coexistent autoimmune diseases are called overlap syndromes. Due to the distinct clinical picture[1], the extent of damage in SSc-overlap may be affected compared to pure-SSc.ObjectivesTo identify differences in the time course and characteristics of damage between pure-SSc and SSc-overlap patients by evaluating the Scleroderma Clinical Trials Consortium-Damage Index (SCTC-DI)[2].MethodsSingle tertiary care centre observational study with 160 enrolled SSc patients. Eighty-eight patients (55%) had diffuse cutaneous SSc (dcSSc), 86% were female and median disease duration was 9 years/4;16/. SSc-overlap was diagnosed based on the evaluation of the attending physicians. SCTC-DI was calculated. SCTC-DI score between 6-12 was considered as moderate and >12 points as severe damage. Damage profile of pure-SSc and SSc-overlap including subsets was compared.ResultsSSc-overlap was present in 24% of cases (n=39; 18 rheumatoid arthritis, 12 Sjögren, 12 myositis, 1 antiphospholipid syndrome). Age at enrolment and at disease onset, dcSSc/limited cutaneous (lcSSc) ratio, disease duration and gender distribution showed no difference between pure-SSc and SSc-overlap. Pure-SSc and SSc-overlap patients, including lcSSc/dcSSc subset comparison had the same damage burden (Kruskal-Wallis p>0.05). Median/IQR/ SCTC-DI was similar in pure-SSc and SSc-overlap (9/7;14/ and 9/6;13/ respectively). Moderate damage was found in around 53% and severe damage in 28% of patients in both pure-SSc and SSc-overlap. Gastrointestinal, cardiopulmonary, cardiac, vascular and renal domains of SCTC-DI did not differ between SSc-overlap and pure-SSc, whereas proximal muscle weakness was more prevalent in SSc-overlap compared to pure-SSc. ILD was scored similarly frequently in pure-dcSSc and dcSSc-overlap (82% vs 66.7%, χ² p>0.05), however, it was also present in 65% of pure-lcSSc and 60% of lcSSc-overlap patients. Severe damage was more prevalent in SSc-overlap patients at early stage of SSc (≤3 years duration, Fisher’s p=0.029) compared to pure-SSc. Early severe damage was more frequent in dcSSc-overlap compared to pure-dcSSc (Fisher’s p=0.042). Although in pure-SSc there were weak—to-moderate correlations between the SCTC-DI, age, and disease duration (Spearman’s rho:.360-.498;p<0.001), no such associations were found in SSc-overlap patients. Differences in SCTC-DI items in pure-SSc and SSc-overlap are shown in Table 1.Table 1.Differences in SCTC-DI items in SSc-overlap and pure-SScn (%)pure-SSc n=121SSc-overlap n=39pure-dcSSc n=67pure-lcSSc n=54dcSSc-overlap n=21lcSSc-overlap n=18Small joint CC59 (48.8)21 (53.8)d41 (61.2)a18 (33.3)14 (66.7)7 (38.9)Large joint CC46 (38.0)19 (48.7)d32 (47.8)a14 (25.9)11 (52.4)8 (44.4)Proximal muscle weakness12/118 (10.2)11/38 (28.9)b, c, d8 (11.9)4/52 (7.7)7 (33.3)e,f4/17 (23.5)Digital ulcers45 (37.2)13 (33.3)31 (46.3)a14 (25.9)9 (42.9)4 (22.2)SSc-ILD76/101 (75.2)21/33 (63.6)50/61 (82)c26/40 (65)12/18 (66.7)9/15 (60)CC: contracturesBold characters: p<0.05.apure-dcSSc vs pure-lcSSc;bpure-SSc – SSc-overlap;cpure-dcSSc – SSc-overlap;dpure-lcSSc – SSc-overlap;epure-SSc – dcSSc-overlap;fpure-dcSSc – dcSSc-overlapConclusionSCTC-DI is a relevant tool to assess damage in SSc-overlap. In this cohort damage was not related to ageing and disease duration in SSc-overlap. Early dcSSc-overlap patients had higher risk to develop severe damage compared to early pure-dcSSc patients based on the SCTC-DI. Pulmonary damage was less frequent in SSc-overlap compared to pure-dcSSc, but similar in pure-dcSSc and dcSSc-overlap patients. As expected, musculoskeletal damage, especially proximal muscle weakness was present in a remarkable proportion of SSc-overlap patients.References[1]Moinzadeh P et al.; Ann Rheum Dis. 2015 Apr;74(4):730-7.[2]Ferdowsi N et al.; Ann Rheum Dis. 2019 Jun;78(6):807-816.AcknowledgementsProject no. TKP2021-EGA-10 has been implemented with the support provided from the National Research, Development and Innovation Fund of Hungary, financed under the TKP2021-EGA funding scheme.Disclosure of InterestsNone Declared.