The widespread implementation of rapid antigen testing in populations (with and without COVID-19 symptoms) is effective in reducing the spread of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Lateral flow devices (LFDs) for detection of SARS-CoV-2 antigen are inexpensive, provide results within minutes, and are highly specific, and although less sensitive than reverse transcription polymerase chain reaction (RT-PCR) for detection of the virus, they can detect most cases with high viral loads, which are the most infectious .
Slovakia conducted large-scale testing from the last week of October to the second week of November 2020, with 65% of the target population receiving rapid antigen testing. Clinical staff used nasopharyngeal swabs for LFD. large-scale testing in Slovakia combined with other prevention and control measures (including closure of secondary schools and restrictions on parties and indoor recreational activities) reduced the prevalence of COVID-19 by 70%.
The UK piloted mass testing in Liverpool in November 2020, after the city had the highest prevalence of COVID-19 in the UK. Slovakia has put more pressure on its citizens than Liverpool to quarantine anyone who does not take the test. Liverpool’s public health service takes testing very seriously as a control measure, but testing in deprived areas is hampered: testing rates are lowest and positive testing rates highest in the most deprived areas. This demonstrates the need to change public perceptions of testing and the importance of quarantining low-income populations when implementing large-scale testing.
Detection results varied with the stage of the population infection rate and prevalence curve. As SARS-CoV-2 infection rates decreased, the proportion of false-positive test results increased, while the number of false-negative test results decreased. For example, at 99.9% specificity and 80% sensitivity, the positive predictive value was 89% when the prevalence was 1%, decreasing to 44% when the prevalence was 0.1%. Due to the low positive predictive value of the test at low prevalence, the UK Department of Public Health recently performed RT-PCR testing to confirm positive LFD results.
The Slovakian pilot was conducted at a time when the prevalence was still high (3.9% in the area with the highest infection rate). Rapid antigen testing was used as an additional tool to identify asymptomatic infected individuals who needed to be isolated. In addition, those who do not agree to participate in testing are asked to be isolated, thereby reducing the chance of transmission. the higher the prevalence of SARS-CoV-2 infection, the greater the number of detectable SARS-CoV-2 infections, but also the higher the proportion of false-negative tests, and therefore the greater the reliance on other control measures. Regardless of prevalence, mass testing should be considered only in conjunction with other protective measures.
At the end of the mass testing program in Slovakia, rapid antigen testing had identified more than 50,000 asymptomatic infections. Although testing technologies are comparable in Slovakia, England and Wales, the interventions are different.
As research continues to clarify the impact of vaccines on SARS-CoV-2 transmission, rapid antigen testing needs to be used as part of a comprehensive public health intervention to reduce the risk of virus escape from vaccines or natural immunity by inhibiting transmission.