Environmental factors influence the efficacy of<unk>  disease transmission; the most evident environmental conditions are temperature and relative humidity. The sum of all the factors that influence temperature and humidity, either meteorological (outdoor) or human (indoor), as well as other circumstances influencing the spread of droplets containing infectious particles, as winds, or human behavior, influence the transmission of<unk>  diseases.<unk>  infections usually land in the respiratory system, with the agent present in aerosols (infectious particles < 5 µm in diameter). This includes dry particles, often the remnant of an evaporated wet particle called nuclei, and wet particles. * Relative humidity (RH) plays an important role in the evaporation of droplets and the distance they travel. 30 μm droplets evaporate in seconds. The CDC recommends a minimum of 40% RH indoors to significantly reduce the infectivity of aerosolized virus. An ideal humidity for preventing aerosol respiratory viral transmission at room temperature appears to be between 40% and 60% RH. If the relative humidity goes below 35% RH, infectious virus stays longer in the air. *The number of rainy days (more important than total precipitation); mean daily sunshine hours; latitude and altitude are relevant when assessing the possibility of spread of<unk>  disease. Some infrequent or exceptional events influence the dissemination of<unk>  diseases, including tropical storms, hurricanes, typhoons, or monsoons. * Climate affects temperature, winds and relative humidity, the main factors affecting the spread, duration and infectiousness of droplets containing infectious particles. The influenza virus spreads easily in the Northern Hemisphere winter due to climate conditions that favour the infectiousness of the virus. * Isolated weather events decrease the concentration of<unk>  fungal spores; a few days later, number of spores increases exponentially. * Socioeconomics has a minor role in<unk>  disease transmission. In cities,<unk>  disease spreads more rapidly than in rural areas and urban outskirts. Rural areas generally favor higher<unk>  fungal dissemination. * Proximity to large bodies of water such as rivers and lakes can enhance<unk>  disease. * Poor maintenance of air conditioning systems has led to outbreaks of Legionella pneumophila. * Hospital-acquired<unk>  diseases are associated with poorly-resourced medical systems, which make isolation challenging. *Air conditioning may reduce transmission by removing contaminated air, but may also contribute to the spread of respiratory secretions inside a room.
Airborne transmission
Vertical transmission
Horizontal transmission
Human-to-human transmission
Intentional contagion of infection
Natural reservoir
Animal bite
Fecal–oral route