key: cord-0688293-q600zdgg authors: Valent, Francesca; Doimo, Anna; Mazzilis, Giada; Pipan, Corrado title: RT-PCR tests for SARS-CoV-2 processed at a large Italian Hospital and false-negative results among confirmed COVID-19 cases date: 2020-06-11 journal: Infection control and hospital epidemiology DOI: 10.1017/ice.2020.290 sha: 96542de6db0e469d9a843e89c143bd14b04bd6bd doc_id: 688293 cord_uid: q600zdgg nan increased progressively exceeding 1,000 by April 9, whereas the proportion of those resulting positive peaked on March 17 (23.5%) and then progressively decreased. Subjects with >1 swab collection were 2,949 (28.1%). The proportion increased from 25.1% among 9,658 subjects with initial negative exam, to 37.3% among 59 with initial invalid exam, to 65.9% among 765 with initial positive result (χ 2 test, P < .0001). The median times from first to second exam were 7, 1, and 11 days, respectively. Of 860 COVID-19 cases, 433 had at least 2 additional swabs after the first positive result. The likelihood of having at least 2 additional swabs decreased significantly among the elderly (χ 2 test, P < .0001) ( Table 1) . Of COVID-19 cases with at least 2 additional exams, 84 (19.4%) had a negative result after the COVID-19 diagnosis, followed by a positive result. The proportion did not vary significantly across age groups (Fisher exact test, P = .1821) ( Table 1) . Among those 84 COVID-19 cases, median time from the negative swab and the following positive swab was 2 days. Only 2 persons had 1 positive result after 2 consecutive negative tests. Negative RT-PCR tests followed, within few days, by a positive result among COVID-19 confirmed cases can be reasonably considered a false negative because the same patients had a positive test immediately afterward. Our population included both symptomatic and asymptomatic SARS-CoV-2 infections. Our results are important not only for hospitalized patients, who might be discharged based on false-negative results but also for asymptomatic cases who might break isolation based on tests that might by not reliable. If those persons are still infectious, they can spread the virus in the community. Lippi et al 6 described potential RT-PCR vulnerabilities that may affect the diagnostic accuracy of this technique, including both general preanalytical issues (collection, handling, transport and storage of the swabs, quality and volume of the collected material, interference from other substances) and analytical issues (choosing the right diagnostic window, validation of assays, harmonization, instrument functioning). Ways to minimize the risk of diagnostic errors include repeated collection of specimens in patients with suspicion of infection, training on swab collection, quality assurance for analytical procedures, and combination of clinical evidence with RT-PCR results. 6 Laboratory parameters, such as lactate dehydrogenase, C-reactive protein, alanine aminotransferase, neutrophil count, 7 and results of chest computed tomography 8 can help define the disease stage. We were able to assess only the proportion of false-negative tests among subjects with multiple swabs collected after a positive test. Conversely, if a subject had a negative test (either the first or another one) and no further swabs, it was not possible to assess whether the test was truly negative. Nonetheless, we assume that our results are generalizable to all tests. Thus, a first negative result should not be sufficient to neglect social distancing measures or use of personal protective equipment. For a better understanding of the role and diagnostic accuracy of RT-PCR for SARS-CoV-2, further research should be conducted to assess viral load in respiratory specimens in patients with different severity of infection and at different time points. Ethical considerations. All procedures contributing to this work comply with the Declaration of Helsinki. The analyses were based on anonymous administrative data, therefore patient consent and Ethical Committee approval were not required in Italy. Situazione in Italia. Ministero della Salute website Ministero della Salute website Laboratory testing for coronavirus disease (COVID-19) in suspected human cases. World Health Organization website Stability issues of RT-PCR testing of SARS-CoV-2 for hospitalized patients clinically diagnosed with COVID-19 False-negative of RT-PCR and prolonged nucleic acid conversion in COVID-19: rather than recurrence Potential preanalytical and analytical vulnerabilities in the laboratory diagnosis of coronavirus disease 2019 (COVID-19) Laboratory parameters in detection of COVID-19 patients with positive RT-PCR; a diagnostic accuracy study False-negative results of real-time reversetranscriptase polymerase chain reaction for severe acute respiratory syndrome coronavirus 2: role of deep-learning-based CT diagnosis and insights from two cases Acknowledgments. None.Financial support. No financial support was provided relevant to this article. All authors report no conflicts of interest relevant to this article.