A wind speed threshold for increased outdoor transmission of coronavirus: an ecological study

Background To examine whether outdoor transmission may contribute to the COVID-19 epidemic, we hypothesized that slower outdoor wind speed is associated with increased risk of transmission when individuals socialize outside. Methods Daily COVID-19 incidence reported in Suffolk County, NY, between March 16th and December 31st, 2020, was the outcome. Average wind speed and maximal daily temperature were collated by the National Oceanic and Atmospheric Administration. Negative binomial regression was used to model incidence rates while adjusting for susceptible population size. Results Cases were very high in the initial wave but diminished once lockdown procedures were enacted. Most days between May 1st, 2020, and October 24th, 2020, had temperatures 16–28 °C and wind speed diminished slowly over the year and began to increase again in December 2020. Unadjusted and multivariable-adjusted analyses revealed that days with temperatures ranging between 16 and 28 °C where wind speed was < 8.85 km per hour (KPH) had increased COVID-19 incidence (aIRR = 1.45, 95% C.I. = [1.28–1.64], P < 0.001) as compared to days with average wind speed ≥ 8.85 KPH. Conclusion Throughout the U.S. epidemic, the role of outdoor shared spaces such as parks and beaches has been a topic of considerable interest. This study suggests that outdoor transmission of COVID-19 may occur by noting that the risk of transmission of COVID-19 in the summer was higher on days with low wind speed. Outdoor use of increased physical distance between individuals, improved air circulation, and use of masks may be helpful in some outdoor environments where airflow is limited.

Exposure-lag Response of Air Temperature on COVID-19 Incidence in Italy

The exposure-lag response of air temperature on COVID-19 incidence is unclear and there have been concerns regarding the robustness of previous studies. Here we present an analysis of high spatial and temporal resolution using the distributed lag non-linear modelling (DLNM) framework. We first fit statistical models to select Italian cities, accounting for lag effects up to 10 days and several categories of potential confounders (policy, mobility, meteorological, and pollution variables). Estimates from these models are then synthesised using random effects meta-analysis to yield pooled estimates of the exposure-lag response presented as the relative risk (RR) and cumulative RR (RRcum). Though there was variation in the lag-specific exposure-response curves, the cumulative exposure response was approximately bell shaped, with highest risk at 19.8 °C, 2.39 [95% CI: 1.13; 2.94] times that at 4.7 °C which represented the lowest risk. Our work is in agreement with studies suggesting “lower” and “higher” temperatures might reduce covid-19 transmission, though our results suggest the optimum temperature for outdoor transmission might be higher than previously thought. Due to this uncertainty, our work underscores the need for facemasks and social distancing even in warm temperatures.

Indoor versus outdoor transmission of SARS-COV-2: environmental factors in virus spread and underestimated sources of risk

The first case of Coronavirus Disease 2019 (COVID-19), which is caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), in Europe was officially confirmed in February 2020. On 11 March 2020, after thousands of deaths from this disease had been reported worldwide, the WHO changed their classification of COVID-19 from a public health emergency of international concern to a pandemic. The SARS-CoV-2 virus has been shown to be much more resistant to environmental degradation than other coated viruses. Several studies have shown that environmental conditions can influence its viability and infectivity. This review summarizes current knowledge on the transmission pathways of the novel coronavirus, and directs attention towards potentially underestimated factors that affect its propagation, notably indoor spread and outdoor risk sources. The contributions of significant indoor factors such as ventilation systems to the spread of this virus need to be carefully ascertained. Outdoor risk sources such as aerosolized particles emitted during wastewater treatment and particulate matter (PM), both of which may act as virus carriers, should be examined as well. This study shows the influence of certain underestimated factors on the environmental behavior and survival of the SARS-CoV-2 virus. These aspects of coronavirus propagation need to be accounted for when devising actions to limit not only the current pandemic but also future outbreaks. Graphic abstract

Outdoor transmission of COVID-19: Analysis of windspeed

BackgroundTo examine whether outdoor exposures may contribute to the COVID-19 epidemic, we hypothesized that slower outdoor windspeed is associated with increased risk of transmission when individuals socialize outside.MethodsDaily COVID-19 incidence reported between 3/16/2020-12/31/2020 was the outcome. Average windspeed and maximal daily temperature were derived from the National Oceanic and Atmospheric Administration. Negative binomial regression was used to model incidence, adjusting for susceptible population size.ResultsCases were very high in the initial wave but diminished quickly once lockdown procedures were enacted. Unadjusted and multivariable-adjusted analyses revealed that warmer days with windspeed <5.5 MPH had increased COVID-19 incidence (aIRR=1.50, 95% C.I.=[1.25-1.81], P<0.001) as compared to days with average windspeed ≥5.5 MPH.ConclusionThis study suggests that outdoor transmission of COVID-19 may occur by noting that the risk of transmission of COVID-19 in the summer was highest on days when wind was reduced.

Outdoor Transmission of SARS-CoV-2 and Other Respiratory Viruses, a Systematic Review

Background While risk of outdoor transmission of respiratory viral infections is hypothesized to be low, there is limited data of SARS-CoV-2 transmission in outdoor compared to indoor settings. Methods We conducted a systematic review of peer-reviewed papers indexed in PubMed, EMBASE and Web of Science and pre-prints in Europe PMC through August 12 th, 2020 that described cases of human transmission of SARS-CoV-2. Reports of other respiratory virus transmission were included for reference. Results Five identified studies found that a low proportion of reported global SARS-CoV-2 infections have occurred outdoors (&lt;10%) and the odds of indoor transmission was very high compared to outdoors (18.7 times; 95% CI 6.0, 57.9). Five studies described influenza transmission outdoors and two described adenovirus transmission outdoors. There was high heterogeneity in study quality and individual definitions of outdoor settings which limited our ability to draw conclusions about outdoor transmission risks. In general, factors such as duration and frequency of personal contact, lack of personal protective equipment and occasional indoor gathering during a largely outdoor experience were associated with outdoor reports of infection. Conclusion Existing evidence supports the wide-held belief that the the risk of SARS-CoV-2 transmission is lower outdoors but there are significant gaps in our understanding of specific pathways.

Long-lasting microbial larvicides for controlling insecticide resistant and outdoor transmitting vectors: a cost-effective supplement for malaria interventions

The issues of pyrethroid resistance and outdoor malaria parasite transmission have prompted the WHO to call for the development and adoption of viable alternative vector control methods. Larval source management is one of the core malaria vector interventions recommended by the Ministry of Health in many African countries, but it is rarely implemented due to concerns on its cost-effectiveness. New long-lasting microbial larvicide can be a promising cost-effective supplement to current vector control and elimination methods because microbial larvicide uses killing mechanisms different from pyrethroids and other chemical insecticides. It has been shown to be effective in reducing the overall vector abundance and thus both indoor and outdoor transmission. In our opinion, the long-lasting formulation can potentially reduce the cost of larvicide field application, and should be evaluated for its cost-effectiveness, resistance development, and impact on non-target organisms when integrating with other malaria vector control measures. In this opinion, we highlight that long-lasting microbial larvicide can be a potential cost-effective product that complements current front-line long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) programs for malaria control and elimination. Microbial larviciding targets immature mosquitoes, reduces both indoor and outdoor transmission and is not affected by vector resistance to synthetic insecticides. This control method is a shift from the conventional LLINs and IRS programs that mainly target indoor-biting and resting adult mosquitoes.

Rapid Scoping Review of Evidence of Outdoor Transmission of COVID-19

The COVID-19 pandemic is both a global health crisis, and a civic emergency for national governments, including the UK. As countries across the world loosen their lockdown restrictions, the assumption is generally made that the risk of COVID-19 transmission is lower outdoors, and this assumption has shaped decisions about what activities can re-commence, the circumstances in which they should re-commence, and the conditions under which they should re-commence. This is important for events and activities that generate outdoor gatherings of people, including both participatory and spectator sport events, protests, concerts, carnivals, festivals, and other celebrations. The review, which was designed to be undertaken rapidly in 15 days, returned 14 sources of evidence of outdoor transmission of COVID-19, and a further 21 sources that were used to set the context and understand the caveats that should be considered in interpreting the review findings. The review found very few examples of outdoor transmission of COVID-19 in everyday life among c. 25,000 cases considered, suggesting a very low risk. However risk of outdoor transmission increases when the natural social distancing of everyday life is breached, and gathering density, circulation and size increases, particularly for an extended duration. There was also evidence that weather had a behavioural effect on transmission, with temperatures that encourage outdoor activity associated with lower COVID-19 transmission. Due to lack of surveillance and tracing systems, and confounding factors and variables, there was no evidence that robustly tested transmission at outdoor mass gatherings (circa 10,000+ people), which are as likely to generate transmission from the activities they prompt (e.g. communal travel and congregation in bars) as from outdoor transmission at the gathering itself. The goal of hosts and organisers of events and activities that generate outdoor gatherings of people is to prevent the escalation of risk from sporadic transmission to the risk of transmission through a cluster outbreak. Considerations for such hosts and organisers include: (1) does the gathering prompt other behaviours that might increase transmission risk?; (2) for each part of the event or activity, how dense is the gathering, how much do people circulate, how large is the gathering, and how long are people there?; (3) is rapid contact tracing possible in the event of an outbreak? These considerations should take place relevant to the size of the underlying risk, which includes the rate of infection in the community and the likely attendance of vulnerable groups. Risk must be balanced and mitigated across the risk factors of density, circulation, size and duration. No one risk factor presents an inherently larger risk than any other, but neither is any one risk factor a magic bullet to eliminate risk. Finally, it is clear that the largest risks from gatherings come from spontaneous or informal unregulated and unmitigated events or activities which do not consider any of the issues, risks and risk factors outlined in this paper

Protocol for a Rapid Scoping Review of Evidence of Outdoor Transmission of COVID-19

The COVID-19 pandemic is both a global health crisis, and a civic emergency for national governments, including the UK. As countries across the world loosen their lockdown restrictions, the assumption is generally made that the risk of COVID-19 transmission is lower outdoors, and this assumption has shaped decisions about what activities can re-commence, the circumstances in which they should re-commence, and the conditions under which they should re-commence. This is important for events and activities that generate mass gatherings, particularly mass participation sports events such as running, but also events in other sectors such as concerts, carnivals and festivals. This paper sets out a protocol for a rapid scoping review of evidence of incidents of outdoor transmission of COVID-19, including the settings, environments and circumstances of such transmission, and their comparative prevalence to incidents of indoor transmission. Its purpose is to inform discussions about the recommencement of activities that generate mass gatherings.