Sensitivity of rapid antigen tests for COVID-19 during the Omicron variant outbreak

BackgroundRapid antigen tests have been used to prevent the spread of the coronavirus disease 2019 (COVID-19); however, there have been concerns about their decreased sensitivity to the Omicron variant. AimsIn this study, we compared the sensitivity and specificity of the rapid antigen and the polymerase chain reaction (PCR) tests among the players and staff members of the Japan Professional Football League and clubs. Furthermore, we evaluated the relationship between the sensitivity and the duration from the onset of the symptoms to testing, the manufacturer of the rapid antigen test kits, and the PCR test analyte. Design and methodsThis was a retrospective observational study. We used 656 results from both the rapid antigen and PCR tests for COVID-19 using the analytes collected on the same day from January 12 to March 2, 2022, during the Omicron variant outbreak in Japan. ResultsThe sensitivity of the rapid antigen test compared with the PCR test was 0.63 (95% confidence interval: 0.54-0.72) and the specificity was 0.998 (95% confidence interval: 0.995-1.000). There were no significant associations between the sensitivity and the duration from the onset of the symptoms to testing (including asymptomatic cases in the category), vaccination status, manufacturer of the rapid antigen test kit or PCR analyte (P > 0.05) with small effect sizes (Cramers V or {varphi}: [≤] 0.22). ConclusionsEven during the Omicron outbreak, the sensitivity of the rapid antigen tests did not depend on the duration from the onset of the symptoms to testing.

Quantifying the effect of isolation and negative certification on COVID-19 transmission

AO_SCPLOWBSTRACTC_SCPLOWO_ST_ABSBackgroundC_ST_ABSIsolation of close contact people and negative test certification are used to manage the spread of new coronavirus infections worldwide. These effectively prevent the spread of infection in advance, but they can lead to a decline in socio-economic activity. Thus, the present study quantified the extent to which isolation and negative test certification respectively reduce the risk of infection. MethodsA discrete-time SEIR model was used as the infectious disease model, and equations for calculating the conditional probability of non-infection status given negative test results on two different days were derived. ResultsThe respective non-infection probabilities with two negative PCR test results, and with one negative PCR test result and one antigen test result, were quantified. By substituting initial parameters of the SEIR model into these probabilities, the present study revealed the following: (1) isolating close contact individuals can reduce by 80% the risk of infection during the first five days, but five more days are needed to reduce the risk 10% more, and seven more days to reduce the risk 20% more; and (2) if an individual with a negative PCR test result has a negative antigen test result the next day, then his or her infection probability is between 0.6% and 0.7%. ConclusionsFive-day isolation has a proportionally greater effect on risk reduction, compared to longer isolation; and thus, if an isolation period of longer than five days is contemplated, both the risk reduction and the negative effects from such increased isolation should be considered. Regarding negative test certification, our results provide those in managerial positions, who must decide whether to accept the risk and hold mass-gathering events, with quantitative information that may be useful in their decision-making.

COVID-19 testing systems and their effectiveness in small, semi-isolated groups for sports events

In this study, we quantitatively assessed the effectiveness of systems for COVID-19 testing in small groups of sport teams that are semi-isolated from the general population by countermeasures against infection. Two types of group were assumed, and the dynamics of infection within each group was modeled by using a compartment model of infectious disease. One group (Group A) comprised domestic professional sports teams that play many games over a season while remaining within a relatively small region. Polymerase chain reaction (PCR) tests were routinely conducted once every 2 weeks, and the number of infected individuals that could not be removed after identification by testing or checking for symptoms was defined as the risk. The other group (Group B) comprised teams that travel across borders for mass-gathering events like the Olympic and Paralympic Games. The teams were isolated for 2 weeks at their destination; frequent testing and checking for symptoms was conducted, and any infected individuals were removed. The number of infected individuals participating in games after the isolation period was defined as the risk. In Group A, the number of infected individuals detected by routinely conducted PCR testing was lower than the number of infected individuals detected by checking for symptoms, indicating that routine testing every 2 weeks was not very effective. In Group B, daily PCR testing was the most effective, followed by daily antigen testing. Dual testing, in which individuals with a positive antigen test were given an additional PCR test, was the least effective with an effect equal to PCR testing every other day. These results indicate that repeated testing does not necessarily increase the detection of infected individuals.