Tanmay Mitra

Background: During the first wave of COVID-19, hospital and intensive care unit beds got overwhelmed in Italy leading to an increased death burden. Based on data from Italian regions, we disentangled the impact of various factors contributing to the bottleneck situation of health care facilities, not well addressed in classical SEIR-like models. A particular emphasis was set on the dark figure, on the dynamically changing hospital capacity, and on different testing, contact tracing, quarantine strategies. Methods: We first estimated the dark figure for different Italian regions. Using parameter estimates from literature and, alternatively, with parameters derived from a fit to the initial phase of COVID-19 spread, the model was optimized to fit data (infected, hospitalized, ICU, dead) published by the Italian Civil Protection. Results: We showed that testing influenced the infection dynamics by isolation of newly detected cases and subsequent interruption of infection chains. The time-varying reproduction number ( R _t ) in high testing regions decreased to < 1 earlier compared to the low testing regions. While an early test and isolate (TI) scenario resulted in up to ∼ 32% peak reduction of hospital occupancy, the late TI scenario resulted in an overwhelmed health care system. Conclusions: An early TI strategy would have decreased the overall hospital accessibility drastically and, hence, death toll (∼ 45% reduction in Lombardia) and could have mitigated the lack of health care facilities in the course of the pandemic, but it would not have kept the hospitalization amount within the pre-pandemic hospital limit. We showed that contact tracing and quarantine without testing would have a similar effect and might be an efficient strategy when sufficient test capacities are not available.

Background: Early March 2020, a SARS-CoV-2 outbreak in the ski resort Ischgl in Austria initiated the spread of SARS-CoV-2 throughout Austria and Northern Europe. Methods: Between April 21 and 27, a cross-sectional epidemiologic study targeting the full population of Ischgl (n = 1867), of which 79 % could be included (n = 1473, incl. 214 children), was performed. For each individual, the study involved a SARS-CoV-2 PCR, antibody testing and structured questionnaires. A mathematical model was used to help understand the influence of the determined seroprevalence on virus transmission. Findings: The seroprevalence was 42.4% (95% CI 39.8–44.7). Individuals under 18 showed a significantly lower seroprevalence of 27.1% (95% CI 21.3–33.6) than adults (45%; 95% CI 42.2–47.7; OR of 0.455, 95% CI 0.356–0.682, p< 0.001). Of the seropositive individuals, 83.7% had not been diagnosed to have had SARS-CoV-2 infection previously. The clinical course was generally mild. Over the previous two months, two COVID-19-related deaths had been recorded, corresponding to an infection fatality rate (IFR) of 0.25% (95% CI 0.03–0.91). Only 8 (0.5 %) individuals were newly diagnosed to be infected with SARS-CoV-2 during this study. Interpretation: Ischgl was hit early and hard by SARS-CoV-2 leading to a high local seroprevalence of 42.4%, which was lower in individuals below the age of 18 than in adults. Mathematical modeling suggests that a drastic decline of newly infected individuals in Ischgl by the end of April occured due to the dual impact from the non-pharmacological interventions (NPIs) and a significant immunization of the Ischgl population. Funding: Helmholtz Association, European Union’s Horizon 2020 research and innovation program, German Research Foundation (DFG), state Tyrol.