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JMIR Public Health Surveill ; 2023 May 24.
Article in English | MEDLINE | ID: covidwho-20234741


BACKGROUND: The SARS-CoV-2 pandemic is characterized by a constant risk of a rapid increase in infection burden due to the emergence of new variants with higher transmissibility and immune escape. Monitoring the SARS-CoV-2 pandemic has so far mainly relied on passive surveillance, which yields biased epidemiological measures due to the disproportionate number of undetected asymptomatic cases. In contrast, active surveillance could provide more accurate estimates of the true SARS-CoV-2 prevalence that help to forecast the evolution of the pandemic, enabling evidence-based decision-making. OBJECTIVE: The objective of this study was to compare four different approaches of active SARS-CoV-2 surveillance, focusing on feasibility and epidemiological outcomes. METHODS: The randomized, two-factor factorial, multi-arm parallel trial was conducted in 2020 in a German district with 700,000 inhabitants. The epidemiological outcome comprised the SARS-CoV-2 prevalence and its precision. The four study arms combined two factors: i) individuals versus households, ii) direct testing versus testing conditioned on symptom pre-screening. Individuals seven years and older were eligible. Altogether, 27,908 addresses from general population representative samples of 51 municipalities were randomly allocated to the arms and 15 consecutive recruitment weekdays. Data collection and logistics were highly digitized, a website in five languages enabled low-barrier registration and tracking of results. Gargle sample collection kits were sent by post. Participants collected a gargle sample at home and mailed it to the laboratory. Samples were analyzed with RT-LAMP, positive/weak results were confirmed with RT-qPCR. RESULTS: Recruitment took place between 18 November and 11 December 2020. The response rates in the four arms varied between 34% and 41%. The pre-screening classified 17% as COVID-19 symptomatic. Altogether, 4,232 persons without pre-screening and 7,623 participating in the pre-screening provided 5,351 gargle samples, of which 5,319 (99%) could be analyzed, yielding 17 confirmed SARS-CoV-2 infections and a combined prevalence of 0.36% (95% CI [0.14%; 0.59%]) in the arms without, respectively 0.05% (95% CI [0.00%; 0.108%]) with pre-screening (initial contacts only). In more detail, we found a prevalence of 0.31% (95% CI [0.06; 0.58]), respectively 0.35% (95% CI [0.09; 0.6], household members included), and lower estimates with pre-screening (0.07% (95% CI [0.0; 0.15], respectively with household members 0.02 (95% CI [0.0; 0.06]). Asymptomatic infections occurred in 3/11 positive cases with symptom data. The two arms without pre-screening performed best regarding effectiveness and accuracy. CONCLUSIONS: This study has shown that the combination of postal mailing of gargle sample kits as well as returning home-based self-collected liquid gargle samples and a subsequent analysis with high-sensitivity RT-LAMP is generally a feasible way to conduct active SARS-CoV-2 population surveillance without burdening routine diagnostic testing. Efforts to improve participation rates and to facilitate integration into the public health system may increase the potential to effectively monitor the course of the pandemic. CLINICALTRIAL: The trial was registered (30 November 2020) at the German Clinical Trials Register, registration number DRKS00023271. INTERNATIONAL REGISTERED REPORT: RR2-10.1186/s13063-021-05619-5.