Both bacterial and fungal spores float easily, and they exist in the stratosphere.

Due to the lack of nutrition and proper temperature in the air, bacteria cannot reproduce and are often destroyed by sunlight and dryness. Only bacteria and fungi or bacterial spores with strong resistance can survive for a long time. Bacillus, pigment-producing bacteria and fungal spores are common in outdoor air; There are more microorganisms in indoor air than outdoor air, especially in densely populated public places, hospital wards, clinics and other places, which are easily polluted by carriers and patients. Such as droplets, dander, sputum, purulent sweat, feces and so on, carry a large number of microorganisms, which can seriously pollute the air. Some medical operations will also cause air pollution, such as high-speed dental drill repair or ultrasonic cleaning of dental calculus, which will produce microbial aerosol; When dressing and making the bed, the microorganisms on the fabric surface fly into the air, and the dust flying field for cleaning and people walking is also the source of microorganisms in the hospital air. The common pathogens in indoor air are Neisseria meningitidis, mycobacterium tuberculosis, hemolytic cocci, diphtheria bacilli and pertussis bacilli. There is a certain relationship between the degree of microbial pollution in the air and the nosocomial infection rate. Hemolytic Streptococcus A is sometimes used as an indicator bacteria in air bacterial hygiene inspection, indicating the degree of air pollution by microorganisms in human upper respiratory tract secretions.