Positive Predictive Value of Rapid Antigen Tests in School During SARS-CoV-2 Omicron Variant Surge : The Pediatric Infectious Disease Journal

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Positive Predictive Value of Rapid Antigen Tests in School During SARS-CoV-2 Omicron Variant Surge

Jang, Eun Jung MPH*; Choe, Young June MD; Yun, Go-Woon MS*; Kim, Ryu Kyung MS*; Jeong, Heegwon BS; Lee, Sangwon PhD*; Park, Young-Joon MD, MPH*

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The Pediatric Infectious Disease Journal 42(1):p e6-e8, January 2023. | DOI: 10.1097/INF.0000000000003751


The coronavirus disease 2019 (COVID-19) has led to the closure of schools worldwide, resulting in significant disruption in children’s learning.1 In South Korea, schools K-12 and universities opened in the spring of 2022 during the Omicron variant surge.2 The Ministry of Education introduced guidelines outlining the use of random screening in the rapid antigen test (RAT) for symptomatic and asymptomatic students and teachers/staff.3 RAT aims to provide timely identification of infection, but there are concerns regarding the positive predictive value of testing.4 This study investigated the true and false positives of the RAT in a large sample of students and teachers/staff serially screened throughout South Korea during the SARS-CoV-2 Omicron variant surge.


Since March 2022, nationwide RAT screening for SARS-CoV-2 has been implemented in kindergartens (4–6 years of age), elementary schools (grades 1–6), middle schools (grades 7–9) and high schools (grades 10–12). Students with and without symptoms were tested twice weekly, and teacher/staff were screened once weekly. Those who had a close contact history with patients with SARS-CoV-2 were screened 3 times per week voluntarily. Each student was asked to report about symptoms (multiple choice), including fever, chills, cough, headache, myalgia, sore throat, runny nose, loss of taste/smell, fatigue, nausea, vomiting or diarrhea. The RAT results were reported through the Student Health Self-Diagnosis App developed by the Ministry of Education. If the RAT result was positive, the patient would be referred for a confirmatory polymerase chain reaction (PCR) test within 72 hours. We merged the symptoms and RAT results data with the PCR data collected between March 2 and April 3, 2022. Individuals with incomplete information (ie, input errors, blank dates) and a history of SARS-CoV-2 infection were excluded from the analysis. The RAT results were compared with the PCR results, and the positive predictive value and binomial 95% confidence intervals were calculated. The weekly positivity rate of COVID-19 in the RAT and PCR was estimated by dividing the number of enrolled students and teachers/staff with COVID-19 by the total number of tested individuals.

The study was reviewed and approved by the Korea Disease Control and Prevention Agency Institutional Review Board (2021-12-03-PE-A).


Between March 2 and April 3, 2022, of the 2,822,544 RAT results collected, 136,902 (4.9%) were positive, of which 126,042 were confirmed by PCR, resulting in a positive predictive value of 92.1% (Table 1). The RAT positivity rate ranged from 68.7% to 83.8% among individuals with symptoms, while the rate ranged from 0.3% to 0.7% in individuals without symptoms (Table 1). The weekly SARS-CoV-2 RAT positivity rate in South Korea ranged from 4.9% to 5.9%, whereas the positive predictive value of RAT ranged from 86.4% to 93.2% (Figure 1, Supplemental Digital Content 1, https://links.lww.com/INF/E851). The positive predictive value was the highest among elementary school students with symptoms (95.7%) and lowest among teachers/staff without symptoms (70.9%) (Table 1). In all groups, the RAT positive predictive value was higher in patients with symptoms than that in those without symptoms (Fig. 1).

TABLE 1. - Result of Nationwide School COVID-19 RAT Screening Reflexed to PCR Confirmation During SARS-CoV-2 Omicron Variant Surge in South Korea, March 2 to April 3, 2022
Symptom* Status Tested Persons RAT Screening Reflex PCR Confirmation
Positive Negative Positive Negative
n % n % n % n %
Symptomatic Students Kindergarten 8974 6872 76.6 2102 23.4 6499 94.6 373 5.4
Elementary school 79,435 56,246 70.8 23,189 29.2 53,820 95.7 2426 4.3
Middle school 36,551 25,119 68.7 11,432 31.3 23,770 94.6 1349 5.4
High school 28,679 20,083 70.0 8596 30.0 18,228 90.8 1855 9.2
Teachers/staffs 13,060 10,943 83.8 2117 16.2 9088 83.1 1855 17.0
Asymptomatic Students Kindergarten 172,746 1133 0.7 171,613 99.3 969 85.5 164 14.5
Elementary school 1,087,744 7534 0.7 1,080,210 99.3 6659 88.4 875 11.6
Middle school 614,195 4568 0.7 609,627 99.3 3773 82.6 795 17.4
High school 474,160 3392 0.7 470,768 99.3 2519 74.3 873 25.7
Teachers/staffs 307,000 1012 0.3 307,000 99.7 717 70.9 295 29.2
Total 2,822,544 136,902 4.9 2,686,654 95.1 126,042 92.1 10,860 7.9
* Symptom refers to fever, chills, cough, headache, myalgia, sore throat, runny nose, loss of taste/smell, fatigue, nausea, vomiting, and diarrhea.
All positive results from RAT screening are reflexed to undergo PCR testing for confirmation.

The positive predictive value of rapid antigen test screening among students and teachers/staff by presence or absence of symptoms (fever, chill, cough, headache, myalgia, sore throat, runny nose, loss of taste/smell, fatigue, nausea, vomiting, and diarrhea).


The overall rate of true positive results among the RAT tests for COVID-19 was high, especially in students with symptoms, which is consistent with other studies.5 Establishing an early diagnosis of COVID-19 requires interpreting test results appropriately. Currently, RAT is widely available and its appropriate use may improve case detection and therefore could reduce transmission and absenteeism.6 As this study was conducted parallel with the policy of returning to school if the RAT result was negative, the results may inform the policymakers to minimize school closure due to the COVID-19 outbreak.

The probability of infection depends on the SARS-CoV-2 prevalence in the community, which was high in South Korea with the Omicron variant surge during the observation period, which increased the performance of RAT in schools.7,8 During the peak of the COVID-19 community outbreak, a positive RAT result is highly likely to represent a true SARS-CoV-2 infection. Furthermore, a negative test result suggests a low possibility of COVID-19. Here, most students presenting with respiratory symptoms and fever with a positive RAT result would have COVID-19, and conversely, if the prevalence is low, positive RAT results are more likely to be false-positive. The study limitations include the convenience sample based on passive surveillance using volunteered symptoms and RAT positivity, therefore may lack clear generalizability. Moreover, reported symptoms were aggregated as symptomatic versus asymptomatic, therefore, we were unable to assess the most significant symptom suggestive of RAT or PCR positivity.

Interpreting SARS-CoV-2 RAT appropriately can provide useful information for decision-making in the educational setting. RAT screening during the community outbreak of SARS-CoV-2 provides a high positive predictive value; therefore, provides helpful information to policymakers to optimize the school health policy.


We thank the Ministry of the Interior and Safety, Si/Do and Si/Gun/Gu, medical health centers staff, and medical facilities for their efforts in responding to the COVID-19 outbreak.


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3. Ministry of Education. COVID-19 related guidelines in education setting [Korean]. Available at: https://www.moe.go.kr/boardCnts/listRenew.do?boardID=72756&renew=72756&m=031304&s=moe. Accessed April 7, 2022.
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6. Schecter-Perkins EM, Doron S, Johnston R, et al. A test-to-stay modified quarantine program for COVID-19 in schools. Pediatrics. 2022;149:e2021055727.
7. Good CB, Hernandez I, Smith K. Interpreting COVID-19 test results: a Bayesian approach. J Gen Intern Med. 2020;35:2490–2491. doi:10.1007/s11606-020-05918-8.
8. Lee JJ, Choe YJ, Jeong H, et al. Importation and transmission of SARS-CoV-2 B.1.1.529 (Omicron) variant of concern in Korea, November 2021. J Korean Med Sci. 2021;36:e346.

rapid antigen test; RAT; COVID-19; SARS-CoV-2; school; screening

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