Bacteria and Viruses

What are bacteria and viruses?
Bacteria and viruses are living organisms that cause diseases, like the common cold or influenza. They also can make some diseases, like asthma, worse.1

How can airborne viruses, bacteria affect health?
Bacteria and viruses can travel through the air, causing diseases and worsening allergies or asthma. They get into the air easily. When someone sneezes or coughs, tiny water or mucous droplets filled with viruses or bacteria scatter. Inhaling these viruses or bacteria can spread coughs, colds, influenza and tuberculosis and other infectious agents.1

Crowded conditions with poor air circulation can promote this spread. Some bacteria and viruses thrive and circulate through poorly maintained building ventilation systems, as with Legionnaires’ disease. Damp, humid air can increase the survival rate of viruses indoors.1

In addition, some individuals with allergies react to endotoxins, substances that come from the broken-down cells of dead bacteria. These microscopic particles have been associated with coughing, wheezing and worsening asthma. Even so, some studies have linked them to protecting against some health threats.1, 2

Bacteria in the soil produce endotoxins, so they are virtually everywhere outdoors. They can come indoors with pets, pests, humidifiers, kitchen compost bins and outdoor air. Walking, dry mopping and other activities can cause them to become airborne once inside.

How to reduce the spread of bacteria, viruses

Most often, the human occupants of a home or workplace are the source of infectious diseases. A key step to reduce the spread of disease through indoor air is to practice healthy behavior. Precautions like coughing or sneezing into the bend of your elbow can curb the spread of airborne viruses and bacteria.

Effective ventilation may also help keep bacteria, viruses and other pollutants out of the indoor air. Research shows that air flow and ventilation can affect how diseases spread indoors. The more stagnant the air is, the more likely diseases are to spread.3

Ventilation can also limit moisture. Damp indoor spaces foster the growth and transmission of viruses and bacteria.3 Controlling moisture indoors can limit the spread of these infectious diseases and also limit mold, dust mite and cockroach growth.4

Should you test the air for bacteria and viruses?
Sampling for all airborne viruses and bacteria is not the best way to determine the cause of specific health problems. Even if you test, it is nearly impossible to know which biological pollutants cause which symptoms or health problems. The amount of most biological substances required to cause disease is unknown and varies from one person to the next.


  1. California Air Resources Board. Report to the California Legislature: Indoor Air Pollution in California. California Environmental Protection Agency. Sacramento, CA. 2005.
  2. Institute of Medicine, Division of Health Promotion, Indoor Air and Disease Prevention. Clearing the Air: Asthma and Indoor Air Exposures. Washington, DC: National Academies Press, 2000.
  3. Li Y, Leung GM, Tang JW, Yang X, et al. Role of Ventilation in Airborne Transmission of Infectious Agents in the Built Environment – A Multidisciplinary Systematic Review. Indoor Air 17, no. 1 (2007): 2-18.
  4. Institute of Medicine, Division of Health Promotion. Damp Indoor Spaces and Health. Washington, DC: National Academies Press, 2004.