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There are so far no intervention studies investigating biocides in air conditioning systems. -The sick building syndrome (SBS) consists of a group of mucosal, skin, and general symptoms that are temporally related to working in particular buildings. It is the workers who are symptomatic, but the building or its services which are the cause. The common symptoms and a method of assessment are shown in box 2. The average number of work related symptoms per occupant is known as the building symptom index. It can be measured reproducibly by simple questionnaire surveys. The building symptom index shows a wide variation between different buildings (fig 1); “sicker” buildings often have conditions of air temperature, humidity, and lighting levels that fully comply with current standards. Some of the reproducible “facts” shown in studies in different countries are shown in box 1, and factors related to higher (sicker) building symptom indices shown in box 3. Box 4 shows the WHO standards for the management of building ventilation systems. Money spent on the building services is likely to be cost effective in terms of the lost productivity in symptomatic workers. Figure 1 Range of building symptom indices in a group of buildings studied with the same questionnaire with a maximum of 10 symptoms (the actual BSI is dependent on the number of possible positive answers and differs between questionnaires). ### Box 1: Reproducible observations related to sick building syndrome (?facts)

**!!!!*** "Airborne spread from undiagnosed infections will continuously undermine the effectiveness of even the most vigorous testing, tracing, and social distancing programs." "Aerosols can accumulate, remain infectious in indoor air for hours, and be easily inhaled deep into the lungs. A competition between droplet size, inertia, gravity, and evaporation determines how far emitted droplets and aerosols will travel in air. Larger respiratory droplets will undergo gravitational settling faster than they evaporate, contaminating surfaces and leading to contact transmission. Smaller droplets and aerosols will evaporate faster than they can settle, are buoyant, and thus can be affected by air currents, which can transport them over longer distances. ...Respiratory droplet size has been shown to affect the severity of disease. For example, influenza virus is more commonly contained in aerosols with sizes below 1 µm (submicron), which lead to more severe infection. In the case of (SARS-CoV-2), it is possible that submicron virus-containing aerosols are being transferred deep into the alveolar region of the lungs, where immune responses seem to be temporarily bypassed. SARS-CoV-2 has been shown to replicate three times faster than SARS-CoV-1 and thus can rapidly spread to the pharynx, from which it can be shed before the innate immune response becomes activated and produces symptoms. By the time symptoms occur, the patient has transmitted the virus without knowing.... The US CDC recommendations... are based on studies of respiratory droplets carried out in the 1930s. In outdoor environments, numerous factors will determine the concentrations and distance traveled, and whether respiratory viruses remain infectious in aerosols. Overall, the probability of becoming infected indoors will depend on the total amount of SARS-CoV-2 inhaled. Ultimately, the amount of ventilation, number of people, how long one visits an indoor facility, and activities that affect airflow will all modulate viral transmission pathways and exposure. Universal masking is highly important."

The practice of social distancing and wearing masks has been popular worldwide in combating the contraction of COVID-19. Undeniably, although such practices help control the COVID-19 pandemic to a greater extent, the complete control of virus-laden droplet ...

Physical filtration efficiencies may not directly translate to effectiveness in mitigating virus transmission. More effectiveness studies with biological measures (e.g. viral load and infection events) as outcomes are needed.

An inactivation of airborne pathogenic Middle East Respiratory Syndrome (MERS-CoV) virus was investigated under controlled laboratory conditions. Two …

Influenza A Virus (IAV) replications start from the deposition of inhaled virus-laden droplets on the epithelial cells in the pulmonary tracts. In ord…

The impact of ambient relative humidity (RH) and airflow patterns on the evaporation and dispersion of infectious droplets exhaled from an infector wa…

(2020). The coronavirus pandemic and aerosols: Does COVID-19 transmit via expiratory particles? Aerosol Science and Technology: Vol. 54, No. 6, pp. 635-638.

In conclusion, the frequency of indoor and outdoor allergens in state of Qatar, based on skin prick test study showed the dominance of house dust mites, pollen, grasses which are more or less same to other countries with similar and even with different climate. Reduced exposure to these agents will …

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1986. A review of the health effects of relative humidity in indoor environments suggests that relative humidity can affect the incidence of respiratory infections and allergies. Experimental studies on airborne-transmitted infectious bacteria and viruses have ...

The changes in humidity levels during the Diwali festivities have been examined over a period of 13 years at three Indian metro cities: Ahmedabad, New Delhi and Kolkata. A small short term increase in relative humidity even in the absence of transport ...

****"One of the standard rules (Stoke’s Law) applied in engineering calculations to estimate the suspension times of droplets falling under gravity with air resistance, was derived assuming several conditions including that the ambient air is still. So actual suspension times will differ and vary." "Although short-range large-droplet transmission is possible for most respiratory infectious agents, deciding on whether the same agent is also airborne has a potentially huge impact on the types (and costs) of infection control interventions that are required." "Despite the various mechanistic arguments about which organisms can be potentially airborne and therefore aerosol-transmissible, ultimately, the main deciding factor appears to be how many studies using various differing approaches: empirical (clinical, epidemiological), and/or experimental (e.g. using animal models), and/or mechanistic (using airflow tracers and air-sampling) methods, reach the same consensus opinion. Over time, the scientific community will eventually form an impression of the predominant transmission route for that specific agent, even if the conclusion is one of mixed transmission routes, with different routes predominating depending on the specific situations. This is the case for influenza viruses, and is likely the most realistic. Some bacterial and viral infections that have more than one mode of transmission are also anisotropic, like anthrax, plague, tularemia and smallpox: the ***severity of the disease varies depending on the mode of transmission** [37, 89]. Older experimental infection experiments on volunteers suggest that this is the case for influenza, with transmission by aerosols being associated with a more severe illness [14, 90], and some more recent field observations are consistent with this concept [57]. For anisotropic agents, even if a mode of transmission (e.g. aerosols) accounts for only a minority of cases, interruption of that route of transmission may be required if it accounts for the most severe cases."

"The successful transmission of infection via the airborne route relies on several factors, including the survival of the airborne pathogen in the environment as it travels between susceptible hosts. This review summarizes the various environmental factors (particularly temperature and relative humidity) that may affect the airborne survival of viruses, bacteria and fungi, with the aim of highlighting specific aspects of environmental control that may eventually enhance the aerosol or airborne infection control of infectious disease transmission within hospitals."

{Discussion of many control measures.} Several tiny organisms of various size ranges present in air are called airborne particles or bioaerosol which mainly includes live or dead fungi and bacteria, their secondary metabolites, viruses, pollens, etc. which have been related to health issues ...

"The microbial load was not affected significantly by the temperature, relative humidity, working shift, season, and number of visitors, indicating the effectiveness of a well-designed ventilation system to eliminate site-specific variations. ..A significant correlation was only observed between the number of particles with a diameter of > 10 μm and the airborne microbial loading. Thus, passive sampling may not properly reflect the actual concentrations of smaller bioaerosols. In conclusion, HEPA filters in the HVAC system successfully decreased the bioaerosol concentrations in the hospital environment."

A new expiratory droplet investigation system (EDIS) was used to conduct the most comprehensive program of study to date, of the dilution corrected dr…

Recent studies have investigated the efficacy of air-cleaning products against pathogens in the air. A standard method to evaluate the reduction in airborne viruses caused by an air cleaner has been established using a safe bacteriophage instead of pathogenic viruses; the reduction in airborne viru …

The coronavirus disease‐2019 (COVID‐19) pandemic has heightened the awareness of aerosol generation by human expiratory events and their potential role in viral respiratory disease transmission. Concerns over high severe acute respiratory ...

{Viruses-- probly applies to SARS-COV-2} Many airborne viruses have been shown to be sensitive to ambient humidity, yet the mechanisms responsible for this phenomenon remain elusive. We review multiple hypotheses, including water activity, surface inactivation, and salt toxicity, that may account for the association between humidity and viability of viruses in aerosols. We assess the evidence and limitations for each hypothesis based on findings from virology, aerosol science, chemistry, and physics. In addition, we hypothesize that changes in pH within the aerosol that are induced by evaporation may trigger conformational changes of the surface glycoproteins of enveloped viruses and subsequently compromise their infectivity. This hypothesis may explain the differing responses of enveloped viruses to humidity. The precise mechanisms underlying the relationship remain largely unverified, and attaining a complete understanding of them will require an interdisciplinary approach.

(2019). "deeper understanding and more efficient utilization of bioaerosol studies to prevent public health hazards" "Mycotoxins, defined as secondary metabolites of fungi, are harmful indoor-air contaminants associated with mold growth in buildings and are known to cause several diseases such as cancer, hepatitis, and nephritis (Jarvis and Miller 2005). A component in the cell wall of fungi, (1→3)-β-d-glucan, is believed to play a role in pulmonary inflammation, increased sensitivity to endotoxins, and pulmonary embolisms."

This JAMA Insights Clinical Update discusses the need to better understand the dynamics of respiratory disease transmission by better characterizing transmission routes, the role of patient physiology in shaping them, and best approaches for source control in the context of the COVID-19 outbreak.

Humidity has strong impact on influenza survival on stainless steel surfaces. Etc. Contagion on airplanes, esp airborne.

The pandemic outbreak of the novel coronavirus epidemic disease (COVID-19) is spreading like a diffusion-reaction in the world and almost 208 countries and territories are being affected around the globe. It became a sever health and socio-economic problem, ...

It has been confirmed that the coronavirus disease 2019 (COVID-19) can transmit through droplets created when an infected human coughs or sneezes. Accordingly, 1.83-m (6-feet) social distancing is advised to reduce the spread of the disease among humans. This is based on the assumption that no air c …