盛行率對新冠抗原快速檢驗結果的影響

Impact of Prevalence Rate on the Rapid Antigen Test for SARS-CoV-2

目的：新冠病毒即時反轉錄聚合酶連鎖反應（RTPCR）是目前SARS-CoV-2的標準診斷方法，但其操作耗時，無法適用於所有患者。而抗原快篩（RAT）可提供便宜、簡單而快速的診斷。但確認抗原快篩之敏感性與使用策略是相當重要的。我們嘗試以回溯方式了解疾病盛行率對快速抗原快篩結果的影響。
方法：我們收集了2021年5月1日至8月31日，患者因有症狀或無症狀需緊急手術，而至急診進行COVID-19抗原快篩。當陽性結果時，立即隔離並進行RT-PCR檢驗。
結果：共有1,795位個案同時有抗原快篩和RT-PCR結果。於評估抗原快篩在疾病盛行率影響中，5月份陽性預測值（PPV）60％（敏感性：48.0％，特異性96.2％），6月份81％（敏感性：100％，特異性99.2％），7月份12％（敏感性：100％，特異性96.2％），8月份0％（敏感性：0％，特異性97.2％）。而偽陽性率分別為40％、19％、88％、100％。
結論：抗原快篩可以有效篩檢分流病患，並於高盛行率和高危險個案中進行COVID-19感染的確認。然而，抗原快篩之敏感性低於RT-PCR，基於敏感性的限制，陽性結果大多為有症狀的個案，因此仍有一定比例的偽陰性可能。當抗原快篩結果為陰性，進行臨床決策時，仍須以RT-PCR加以驗證。現在SARS-CoV-2已經發現了一些突變和變異株。將來，可能需要了解突變和變異菌株對抗原快篩的敏感性影響。

Purposes: The real-time reverse transcription-polymerase chain reaction (RT-PCR) of viral RNA is the gold standard for the diagnosis of SARS-CoV-2 infection. However, the operations are time-consuming and is, therefore, not suitable for every patient. In contrast, the rapid antigen test (RAT) for SARS-CoV-2 provides rapid and simple COVID-19 diagnosis at low costs. However, it is pivotal to determine the sensitivity and usage strategies of RAT. This study attempts to retrospectively explore the impact of prevalence rate of COVID-19 on RAT results.
Methods: Data from May 1 to August 31, 2021 were retrospectively collected and analyzed. These patients required surgical operations for symptomatic or non-symptomatic diseases, and had been admitted to the emergency departments where they received RAT for COVID-19. Subjects with positive results were quarantined immediately and RT-PCR tests were performed.
Results: A total of 1,795 participants had both RAT and RT-PCR results. The assessment of the effect of the prevalence rate on RAT showed that the positive predictive value (PPV) was 60% in May (sensitivity: 48.0%, specificity: 96.2%), 81% in June (sensitivity: 100%, specificity: 99.2%), 12% in July (sensitivity: 100%, specificity: 96.2%), and 0% in August (sensitivity: 0%, specificity: 97.2%). The false positive rates were 40%, 19%, 88%, and 100%, respectively.
Conclusions: RAT could be used to screen the patients for triage and identify COVID-19 infection given the high prevalence rate among the high-risk population. However, RAT is less sensitive than RT-PCR. Due to the limitation of sensitivity, the majority of the results obtained from symptomatic cases were positive. Therefore, it is still possible that some of these results were false-negatives. The clinical decision-making should still be made based on confirmatory testing with RT-PCR given a negative RAT result. Currently, there are some novel mutations and variant strains of SARS-CoV-2. The impact of mutations and variant strains on the sensitivity of RAT may be explored in the future.