Evaluation of Secondary Chemistry due to Disinfection of Indoor Air with Germicidal Ultraviolet Lamps (preprint)

The disinfection of air using Germicidal Ultraviolet light (GUV) is a long-standing technique, which has received intense attention during the COVID-19 pandemic. GUV generally uses UVC lamps as its light source, which are known to initiate photochemistry in air. However, the impact of GUV on indoor air quality and chemistry has not been investigated in detail, to our knowledge. In this study, we model the chemistry initiated by GUV at 254 or 222 nm ("GUV254" or "GUV222") in a typical room with typical indoor pollutant levels, and for different ventilation levels. GUV254 is irritating for skin and eyes, has an occupational exposure limit, and thus these fixtures typically irradiate a smaller volume near the ceiling, or inside ventilation ducts. In contrast, GUV222 is described by some as harmless to skin or eyes due to rapid absorption in a very thin external layer. Our analysis showed that GUV254 is able to significantly photolyze O3, generating OH radicals, which initiates the oxidation of all indoor volatile organic compounds (VOCs). While secondary organic aerosol (SOA) can be formed as a product of VOC oxidation, most of SOA in our case studies is produced through GUV-independent terpene ozonolysis. GUV254-induced SOA formation is of the order of 0.1-1 g m-3. GUV222 with the same effective virus removal rate makes a smaller impact on indoor air quality, mainly because of the significantly lower UV irradiance needed and substantially less efficient O3 photolysis (for primary OH generation) than at 254 nm.

Indicators for Risk of Airborne Transmission in Shared Indoor Environments and their application to COVID-19 Outbreaks (preprint)

Some infectious diseases, including COVID-19, can be transmitted via aerosols that are emitted by an infectious person and inhaled by susceptible individuals. Although physical distancing effectively reduces short-range airborne transmission, many infections have occurred when sharing room air despite maintaining distancing. We propose two simple parameters as indicators of infection risk for this situation. They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and air cleaning rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend in relation to these parameters that is consistent with an airborne infection model, supporting the importance of airborne transmission for these outbreaks. The observed trends of outbreak size vs. risk parameters allow us to recommend values of the parameters to minimize COVID-19 indoor infection risk. All of the pre-pandemic spaces are in a regime where they are highly sensitive to mitigation efforts. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at much higher risk parameter values. Since both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include ventilation information, to allow expanding our knowledge of the circumstances conducive to airborne transmission of different diseases.

Effects of (Combined) Chinese Medicine on the Risk of Death From COVID-19: A Retrospective Data Analysis Based on 4567 Patients (preprint)

Background The coronavirus disease 2019 (COVID-19) epidemic is still ongoing, but the optimal treatment remains unclear. China adopted a series of measures, including widespread screening, strict quarantine and early treatment, combining western medicine with Chinese medicine, leading to rapid control of its spread. Nevertheless, the effects of ( combined ) Chinese medicine in reducing the toll of COVID-19 lack proof from statistics.Objective We conducted a retrospective data analysis to determine whether ( combined ) Chinese medicine is able to affect patient outcomes and to decrease the risk of death in COVID-19 patients.Methods The data were acquired by outputting the formatting information from the HIS system and then extracting and recording it in the database for complete cases. The demographics, disease onset, treatment, survival/death and all of the clinical classifications, groups and definitions were verified by specialists in the clinic, along with the research methodology and statistics, before conducting the statistical analysis. The characteristics of the cohort and the clinical symptoms and signs, prescriptions and outcomes were described and analyzed by the mean ± SD, median, interquartile range and composition ratio. Analysis of variance was used for comparisons between the measurement data sets; otherwise, the rank sum test was used. Counting data were compared between groups using the chi square test and Fisher’s exact test. Tendency matching was adopted to make the general data balance between groups. A Cox proportional hazard model was used to compare the risk of death among the different groups.Results Four centers were included in our study, and a total of 6,076 patients' clinical records were obtained after combining the data. We included 4567 cases for the descriptive statistics, and the crude case fatality rate was 3.0%. Compared with using only western medicine, (combined) Chinese medicine reduced the risk of death from COVID-19 after adjusting for other prognostic risk factors (HR = 0.135, 95% CI (0.088, 0.208)). Multivariate Cox regression also indicated that when applying the clinical classification of severe/critical, age ≥ 65 years old, coronary heart disease or chronic kidney disease and a time from onset to hospital admission of fewer than 14 days, all of these factors increased the risk of death.Conclusion (Combined) Chinese medicine can significantly reduce the risk of death from COVID-19, but the specific strategy/solution, effects and amount need further exploration in future studies.

BU-Trace: A Permissionless Mobile System for Privacy-Preserving Intelligent Contact Tracing (preprint)

The coronavirus disease 2019 (COVID-19) pandemic has caused an unprecedented health crisis for the global. Digital contact tracing, as a transmission intervention measure, has shown its effectiveness on pandemic control. Despite intensive research on digital contact tracing, existing solutions can hardly meet users' requirements on privacy and convenience. In this paper, we propose BU-Trace, a novel permissionless mobile system for privacy-preserving intelligent contact tracing based on QR code and NFC technologies. First, a user study is conducted to investigate and quantify the user acceptance of a mobile contact tracing system. Second, a decentralized system is proposed to enable contact tracing while protecting user privacy. Third, an intelligent behavior detection algorithm is designed to ease the use of our system. We implement BU-Trace and conduct extensive experiments in several real-world scenarios. The experimental results show that BU-Trace achieves a privacy-preserving and intelligent mobile system for contact tracing without requesting location or other privacy-related permissions.

Exhaled CO2 as COVID-19 infection risk proxy for different indoor environments and activities (preprint)

CO2 is co-exhaled with aerosols containing SARS-CoV-2 by COVID-19 infected people and can be used as a proxy of SARS-CoV-2 concentrations indoors. Indoor CO2 measurements by low-cost sensors hold promise for mass monitoring of indoor aerosol transmission risk for COVID-19 and other respiratory diseases. We derive analytical expressions of CO2-based risk proxies and apply them to various typical indoor environments. Contrary to some earlier recommendations setting a single indoor CO2 threshold, we show that the CO2 level corresponding to a given infection risk varies by over 2 orders of magnitude for different environments and activities. Although large uncertainties, mainly from virus exhalation rates, are still associated with our infection risk estimates, our study provides more specific and practical recommendations for low-cost CO2-based indoor infection risk monitoring.

Epidemiological and clinical characteristics of novel coronavirus infection in children: Thoughts on the diagnostic criteria of suspected cases outside Hubei Province / 中国小儿急救医学

Objective@#To improve the diagnostic criteria of suspected cases through investigating the epidemiological and clinical manifestations of confirmed cases of new-type coronavirus infection in children.@*Methods@#We retrospective analyzed the epidemiological and clinical manifestations of 6 children with new coronavirus infection diagnosed in Chongqing Three Gorges Central Hospital from February 3, 2020 to February 15, 2020 . Compared with the diagnostic criteria of suspected cases,we summarized the problems encountered in the application of this standard in clinical work and try to put forward Suggestions for improvement.@*Results@#Among the 6 children with confirmed cases: 5 males and 1 female; 3 from Hubei Province and 3 from Wanzhou ; 6 cases of clustered onset of the family; Visiting nature: 3 cases of suspected case income, 3 cases of community or outpatient screening . Three cases with fever and / or respiratory symptoms, one of which had symptoms of diarrhea; all children's blood routine and lymphocyte counts were within the normal range; chest CT imaging except for cases No. 1 and No. 5 were in line with typical new coronavirus pneumonia signs. In addition, the remaining 3 patients had abnormal imaging but did not have the characteristics of new coronavirus pneumonia, and 1 case was normal. Comparison results:Only case 1 of all cases fully met the diagnostic criteria, and the remaining cases did not meet the diagnostic criteria of early suspected cases.@*Conclusion@#In order to improve the accuracy and practicality of the diagnosis of suspected cases in children, it is recommended to refine and standardize the diagnostic criteria of some suspected cases.