Biological Agents of Concern in Indoor Environments

When it comes to indoor environments, mold has topped the list of America's most wanted biological agents for the past several years, primarily in response to extensive media coverage, numerous insurance claims and litigation. Legionella also ranks highly as a result of periodic outbreaks of Legionnaire's disease.

The primary reason for concern is microbial agents - fungi (mold and mildew), bacteria and viruses - may cause illnesses, including:

• A variety of infectious diseases. such as tuberculosis, common cold, meningitis, hepatitis and Q fever, chicken pox, measles

• Respiratory infections such as pneumonia; hypersensitivity pneumonitis and humidifier fever to name few

• Allergic reactions

• Toxic effects (mycotoxins)

• Building-related symptoms (also known as sick building syndrome)

• Sensory irritation

With respect to fungi, there are presently no set permissible exposure limits (PELs), recommended exposure limits (RELs) or threshold limit values (TLVs) for fungi in the indoor environment or its byproducts such as mycotoxins and microbial volatile organic compounds  (MVOCs). This is due in part to limited scientific data outside of agricultural or manufacturing settings that support a dose-response relationship; that is if a person is exposed to a certain amount of a particular species of mold or mold byproduct that person will exhibit certain symptoms. It also is due to differences in people. Some people are very sensitive to mold and may show symptoms with very little exposure while others are not as sensitive and may not exhibit any symptoms.

Remember, fungi are ubiquitous. Consequently, it is common to have molds and low levels of other microbial contaminants in all indoor environments. Also remember, microbial agents may not be the cause of illnesses in all cases. Chemicals, such as formaldehyde, other aldehydes and volatile organic compounds (VOCs), off gassing from building materials, office equipment, interior furnishings, textiles, cleaners, pesticides and personal care items also may cause people to have symptoms. As a result, assessing buildings to determine why people are getting sick requires a holistic approach, not just looking at air or settled-dust sampling results. The following tables lists the common fungi (molds and mildew) and bacteria found in indoor environments that also may cause illness:

• Table 1. Common Fungi Known to Produce Reactions or Sensory Irritation

• Table 2. Toxigenic Fungi Commonly Found in Water- or Moisture-Damaged Buildings

• Table 3. Some of the More Common Fungi Found in Indoor Air With Their Accompanying Mycotoxins and Health Effects

• Table 4. Fungi Known to Produce Infectious Disease in Temperate Zones

• Table 5. Bacteria Associated With Respiratory Illnesses, Such as Pneumonia, Hypersensitivity Pneumonitis, Humidifier Fever, and Respiratory Infections

Table 3. Some of the More Common Fungi Found in Indoor Air With Their Accompanying Mycotoxins and Health Effects (1, 2)