Trends and symptoms of SARS-CoV-2 infection: a longitudinal study on an Alpine population representative sample.

OBJECTIVES: The continuous monitoring of SARS-CoV-2 infection waves and the emergence of novel pathogens pose a challenge for effective public health surveillance strategies based on diagnostics. Longitudinal population representative studies on incident events and symptoms of SARS-CoV-2 infection are scarce. We aimed at describing the evolution of the COVID-19 pandemic during 2020 and 2021 through regular monitoring of self-reported symptoms in an Alpine community sample. DESIGN: To this purpose, we designed a longitudinal population representative study, the Cooperative Health Research in South Tyrol COVID-19 study. PARTICIPANTS AND OUTCOME MEASURES: A sample of 845 participants was retrospectively investigated for active and past infections with swab and blood tests, by August 2020, allowing adjusted cumulative incidence estimation. Of them, 700 participants without previous infection or vaccination were followed up monthly until July 2021 for first-time infection and symptom self-reporting: COVID-19 anamnesis, social contacts, lifestyle and sociodemographic data were assessed remotely through digital questionnaires. Temporal symptom trajectories and infection rates were modelled through longitudinal clustering and dynamic correlation analysis. Negative binomial regression and random forest analysis assessed the relative importance of symptoms. RESULTS: At baseline, the cumulative incidence of SARS-CoV-2 infection was 1.10% (95% CI 0.51%, 2.10%). Symptom trajectories mimicked both self-reported and confirmed cases of incident infections. Cluster analysis identified two groups of high-frequency and low-frequency symptoms. Symptoms like fever and loss of smell fell in the low-frequency cluster. Symptoms most discriminative of test positivity (loss of smell, fatigue and joint-muscle aches) confirmed prior evidence. CONCLUSIONS: Regular symptom tracking from population representative samples is an effective screening tool auxiliary to laboratory diagnostics for novel pathogens at critical times, as manifested in this study of COVID-19 patterns. Integrated surveillance systems might benefit from more direct involvement of citizens' active symptom tracking.

Viral particles imaging through evanescent wave scattering in a total internal reflection laser microscope

Optical imaging of objects at the nanometric scale is limited by light diffraction, and for this reason several sub-diffractive optical microscopy techniques have been developed in the last decades. In this article we present an optical laser microscope specifically designed for detection of nano-materials exploiting the Mie scattering between the evanescent wave generated by a laser beam travelling in a transparent substrate through total internal reflection and the nano-objects deposited on the substrate itself. The setup, including the laser source, can be fully integrated inside an optical microscope requiring only a geometric alignment with the substrate thus reducing the complexity and the cost. We also report two possible applications: quantitative detection of Au nanoparticles in the 20–100 nm size range and semi-quantitative detection of virions immobilized on the substrate through bioreceptor / antigen binding, including, but not limited to, SARS-CoV-2. A minimum virus amount of ≈105 in the reaction volume is observed. The results presented here open the route towards unprecedent applications in molecular biology or molecular diagnostics.