key: cord-0844987-8pw4fged
authors: Allievi, Luca; Bongarzoni, Amedeo; Tassinario, Guido; Carugo, Stefano
title: Avoiding COVID‐19 hospital outbreaks: RT‐PCR swab and clinical assessment
date: 2021-07-06
journal: Int J Clin Pract
DOI: 10.1111/ijcp.14231
sha: ff2931a1c47cff8e82d92018adecffcc541785e8
doc_id: 844987
cord_uid: 8pw4fged

nan

sometimes epidemic outbreaks in hospital wards occur.

Nasopharyngeal reverse transcriptase-polymerase chain reaction (RT-PCR) swab test is a fundamental examination in COVID-19 diagnosis. However, several studies have shown a suboptimal sensitivity of this test (around 70% 1 ) in detecting Sars-Cov-2; in an infected patient, the probability of a false-negative result is 67% the day before the symptom onset, 38% the day of symptom onset, 20% 3 days later and then it increases again (to 66% 2 weeks later). 2 In our experience, a critical patient (who then passed away) with strongly suggestive symptoms for COVID-19 had got four consecutive negative RT-PCR swab test results before the positive result on bronchoalveolar lavage.

This high false-negative rate may be caused by (1) the difficulty to perform the nasopharyngeal swab correctly (making this examination operator dependent), (2) a slower rise of the viral load in some patients 3 and (3) the timing of swab tests during the day.

Indeed, RT-PCR test is dependent upon the viral load in detecting Sars-Cov-2, and the probability of having the highest viral load in posterior oropharyngeal saliva in early morning is 61.5%, compared to 23.1% before lunch, 7.7% at 3 PM or before dinner and 0% at bedtime 4 ; therefore, assuming that this also applies to nasopharyngeal secretions, performing a swab at another time of the day could lead to a false-negative result more easily. It is reported that early morning saliva may be a better alternative specimen for detection of Sars-Cov-2. 5 Whatever diagnostic test is used, it is fundamental to identify Sars-Cov-2 infection early to avoid in-hospital contagion. We propose a flowchart for the management of patients who underwent nasopharyngeal RT-PCR swab test (Figure 1 ). If the test result is positive, immediate transfer to a COVID-19 unit should be performed (red zone); if negative without clinical features suggestive for Sars-Cov-2 infection (please see below), no further action needs to be performed (green zone). If the test result is negative but some clinical features may suggest Sars-Cov-2 infection (ie dyspnoea, cough, fever, sore throat, lymphopaenia, fibrinogen, lactate dehydrogenase, C-reactive protein and ferritin above the threshold value, interstitial/ground-glass opacities, etc), the patient should be isolated, physicians should use personal protective equipment (PPE) as in front of a COVID-19 patient and daily clinical and laboratory (body temperature, blood count, C-reactive protein, etc) monitoring and serial RT-PCR swab tests should be performed (grey zone). We must admit that similar findings can be present during other viral infections, but it is equally true that during this phase we must suspect Sars-Cov-2 primarily because of the higher danger and spread velocity compared with other viruses. Weak-positive RT-PCR swab tests should be repeated, but the possible following negative result should be integrated with the clinical assessment as seen before; we remind that RT-PCR swab test has low sensitivity but high specificity (95%) 1 and, therefore, a positive result should never be ignored.

In conclusion, COVID-19 should not be ruled out based on RT-PCR swab test alone, but also the clinical situation should be carefully assessed. 2 A cautious approach integrating RT-PCR swab tests with the clinical assessment may allow to offset the low sensitivity of swab tests and counteract in-hospital epidemic outbreaks. New diagnostic tests are necessary to reach the optimal sensitivity in detecting Sars-Cov-2. We hope that COVID-19 vaccines will help stop

Interpreting a covid-19 test result

Variation in false-negative rate of reverse transcriptase polymerase chain reaction-based SARS-CoV-2 tests by time since exposure

SARS-CoV-2 viral load in saliva rises gradually and to moderate levels in some humans

Early-morning vs spot posterior oropharyngeal saliva for diagnosis of SARS-CoV-2 infection: implication of timing of specimen collection for community-wide screening

Comparing nasopharyngeal swab and early morning saliva for the identification of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)