Twice weekly polymerase chain reaction (PCR) surveillance swabs are not as effective as daily antigen testing for containment of severe acute respiratory coronavirus virus 2 (SARS-CoV-2) outbreaks: A modeling study based on real world data from a child and adolescent psychiatry clinic

Abstract

Objective: In the coronavirus disease 2019 (COVID-19) pandemic, child and adolescent psychiatry wards face the risk of severe acute respiratory coronavirus 2 (SARS-CoV-2) introduction and spread within the facility. In this setting, mask and vaccine mandates are hard to enforce, especially for younger children. Surveillance testing may detect infection early and enable mitigation measures to prevent viral spread. We conducted a modeling study to determine the optimal method and frequency of surveillance testing and to analyze the effect of weekly team meetings on transmission dynamics.

Design and setting: Simulation with an agent-based model reflecting ward structure, work processes, and contact networks from a real-world child and adolescent psychiatry clinic with 4 wards, 40 patients, and 72 healthcare workers.

Methods: We simulated the spread of 2 SARS-CoV-2 variants over 60 days under surveillance testing with polymerase chain reaction (PCR) tests and rapid antigen tests in different scenarios. We measured the size, peak, and the duration of an outbreak. We compared medians and percentage of spillover events to other wards from 1,000 simulations for each setting.

Results: The outbreak size, peak, and duration were dependent on test frequency, test type, SARS-CoV-2 variant, and ward connectivity. Under surveillance conditions, joint staff meetings and therapists shared between wards did not significantly change median outbreak size under surveillance conditions. With daily antigen testing, outbreaks were mostly confined to 1 ward and median outbreak sizes were lower than with twice-weekly PCR testing (1 vs 22; P < .001).

Conclusion: Modeling can help to understand transmission patterns and guide local infection control measures.

Figure 1.

Contact network of a child and adolescent psychiatry clinic with 4 wards. Each dot (node) represents a person. Patients (red), doctors (green), nurses (blue), and therapists (yellow) are connected by a “strong” edge (grey). Additionally, doctors and therapists are connected by a “weak” edge (red), which denotes the connection through weekly meetings.

Figure 2.

Parameters of transmission kinetics for the SARS-CoV-2 omicron variant. (a) Distribution of time to first symptom after exposure; 20% of cases were assumed to be asymptomatic. (b) Distribution of the probability for transmission and for a positive test result from start of symptoms. (c) Distribution of transmission and distribution of a positive test result for asymptomatic cases from day after exposure. Note. Polymerase chain reaction test (o), antigen test (x), and transmission (*).

Figure 3.

Outbreak size without containment through surveillance. Violin plots of 1,000 simulations of outbreak size for the 3 network setups, separated (I), restricted (II), and regular (III) for the SARS-CoV-2 delta variant (a) and the omicron variant (b) when no test strategy was implemented.

Figure 4.

Influence of test frequency on outbreak duration (left panels), peak (middle panels), and size of the outbreak (right panels) in the separated (I), restricted (II), and regular (III) setup. The colored lines denote polymerase chain reaction (PCR) test and rapid antigen tests with different sensitivities (50%, 60%, 70%, and 80%). All data are for the SARS-CoV-2 omicron variant.

Figure 5.

Outbreak size for 2 testing frequencies (every day to every 4 days). Simulations were performed for the SARS-CoV-2 omicron variant with 3 network setups, that is, separated (I), restricted (II), and regular (III), polymerase chain reaction test (1), and rapid antigen tests with 80% sensitivity (2).

Figure 6.

Outbreak size (a) and peak size (b) for no surveillance testing, daily antigen testing, every-second-day antigen testing, every-second-day polymerase chain reaction (PCR) testing, twice-per-week (biweekly) PCR testing with time to report of 1 day, and PCR testing with delayed time-to-report of 2 days. Data shown are for the SARS-CoV-2 omicron variant in the regular setting.