Cornell University Ergonomics Web

DEA3500: Ambient Environment: Biogenic Particles

Viruses

There is evidence that viruses may be spread around an office via the mechanical ventilation system. Viruses are very small particles in the range 0.004 µm -0.08 µm, and they can easily pass through the coarse air filters used in most ventilation systems. Viruses are active outside the body, but once inhaled, many viruses spring into action, like the common cold viruses or influenza viruses. Because colds are relatively commonplace and usually only briefly debilitating we have not given much thought to practices which will reduce the chances of infection. There is also evidence that colds and influenza are transmitted by direct contact, and the risks of infection can be reduced by good personal hygiene, especially frequent hand washing, by avoiding contact with infected colleagues (in Japan some workers even wear face masks to reduce the chances of becoming infected), by using a high efficiency air filtering system in the office, and by lowering your stress level. Many companies and their workers have yet to pursue the potentially huge economic benefits of adopting preventive approaches to lowering the risks of catching viral respiratory infections at work.

Bacteria

Unfortunately, not all building-related illnesses are as transient in their debilitating effects as a common cold. In 1976, at a convention of the American Legionnaires in a Philadelphia hotel, 182 people became ill with an unusual type of pneumonia and 29 people eventually died. Eventually the source of this outbreak was traced to a bacterium which had become entrained in the hotel ventilation system. In recognition of its dramatic entry into public health the disease became known as Legionnaire's disease and the bacterium was named Legionella pneumophila.

Legionella pneumophila occurs naturally in streams, rivers, and reservoirs and it thrives in water that is about neutral in pH (6.9-7.0) and at a temperature around 35 degrees C (95 degrees F). In many air-conditioned buildings the water in the cooling towers that usually are on the roof of the office building meets these requirements and can become contaminated. If the bacterium becomes airborne in a water droplet it can be inhaled. When inhaled into the lungs the Legionella pneumophila. bacterium shows its true colors as an opportunistic pathogen, that is to say it favors infecting someone whose immune system is already depressed by some other factor. Thus, the at risk profile includes older workers, those who smoke, and those whose immune system already is compromised. Although annually some 25-30 otherwise healthy Americans die from Legionnaire's disease associated with contaminated buildings each year, Legionnaire's disease is a major killer of AIDS sufferers. The symptoms of Legionnaire's disease consist of headache, general malaise, myalgia, dry cough, and sometimes gastro-intestinal symptoms, followed by the onset of a high fever and changes in mental abilities. If the disease progresses unchecked it can cause lung damage, respiratory failure and death. These symptoms typically commence between 2 and 10 days after exposure. Other types of Legionella bacteria cause Pontiac fever, which is a flu-like illness lasting 2-5 days and it is probably more common than Legionnaire's disease, but it is not a fatal disease.

Studies of office buildings show that dust from the air filters in the ventilation system contains between 100 and 6,700 bacteria per gram of dust (approximately 2,800 - 190,000 bacteria per ounce of dust), the dust from the ventilation ducts contains between 50 and 50,000 bacteria per gram of dust (approximately 1,400 to 1,400,000 bacteria per ounce of dust), and the floor dust contains similar numbers of bacteria . Endotoxins from the cell walls of dead, gram-negative bacteria may be a cause of sick building syndrome symptoms in some people.

Fungi

We are only just beginning to realize the important effects which fungi can have on indoor air quality in offices. In a survey of over 400 office buildings fungal contamination was found to be responsible for problems in about one third of the buildings. Fungi grow outside and inside buildings and they are everywhere. In fact there are over 100,000 fungal species and they make up a quarter of the biomass of the earth. Providing there is sufficient water, fungi can grow on almost anything, from glass to jet fuel. Most of the fungi responsible for problems inside buildings belong to a group commonly called the molds. Most of us have seen how quickly fruit or bread can go moldy after it has been left exposed to the air. Unfortunately, the interior spaces in office buildings and especially the ventilation systems often provide ideal conditions for rapid mold growth.

Once mold growth has started each mold can produce millions and millions of spores in a very short time. Each spore is like a seed from which a new mold colony can grow providing it settles onto a suitable surface for growth. This new mold colony in turn can then release millions and millions of spores, and so on. Mold spores can be remarkably rugged and in some instances they can still form new colonies more than 12 years after their release into the air. Inhaling these mold spores can produce respiratory reactions of varying severity.

Molds also produce a variety of toxic chemicals including aflatoxins which can cause liver cancer when eaten, and mycotoxins as well as various synergizers which are chemicals that increase the potency of the toxin. Molds also can produce over 500 different VOCs while there is active growth. Some fungi, particularly those which grow on bird or bat droppings, are pathogenic and cause sometimes fatal diseases. Many molds and yeasts cause allergic reactions and it is estimated that up to 15% of people are allergic to fungi. Sherry Rogers, a doctor at the Northeast Center for Environmental Medicine, has found that almost two thirds of patients suffering from "environmental illness" show symptoms of exposure to indoor fungi.

Evidence of fungal contamination of an office building sometimes can be seen or smelled, and if the source is located and removed or treated problems may be resolved (see chapter 4). However, if the fungal contamination is inside the ventilation system it will only be detected by the specialized equipment which a reputable indoor air quality testing firm will use.

Studies of office buildings show that dust from the air filters in the ventilation system contains between 70 and 3,400 fungi per gram of dust (approximately 2,000 - 100,000 fungi per ounce of dust), the dust from the ventilation ducts contains between 70 and 6,200 fungi per gram of dust (approximately 2,000 to 175,000 fungi per ounce of dust), and the floor dust contains similar numbers of fungi.

For more information on different fungal species visit http://www.aerotechlabs.com/reso/fungloss.asp

Hypersensitivity pneumonitis and Humidifier fever

These are respiratory diseases caused by an immune reaction to inhaling aerosols containing various organic materials. It can occur as an acute problem and symptoms of fever, chills, coughing, myalgia, shortness of breath, lethargy and malaise begin some 4 to 6 hours after breathing the contaminated aerosol. These symptoms can persist for another 18 to 24 hours unless re-exposure occurs. With repeated exposures workers symptoms become increasingly severe and eventually lung damage can occur.

Humidifier fever

This disease is thought to be one type of hypersensitivity pneumonitis that can occur inside buildings when workers breath the aerosol from a contaminated humidifier. Various micro-organisms found inside buildings can cause this problem, and these include the thermophilic actinomycetes, a group of filamentous bacteria that like to live in warm temperatures on moist and dirty building materials, a bacterium called Flavobacterium and its endotoxins, molds, and single-celled animals called amoebae that like to live in stagnant water.

Medical researchers studying these problems often use a technique called challenge testing. This basically involves allowing patients to breath for a short time an aerosol containing an extract of the suspected contaminated material, and then tracking physical and subjective responses to this challenge for several hours after inhalation. In this way doctors Peter Sherwood Burge and Alastair Robertson have shown that headache, muscle pains, runny nose, and eye irritation symptoms can start to occur about 4 hours after inhaling water from a contaminated humidifier in a large building and these can persist for many hours after exposure. According to NIOSH data, however, hypersensitivity pneumonitis and related respiratory disorders accounts for only about 3% of health problems in the buildings they have studied.

Dust mites, Insects, Animal Dander, and Pollens

Many indoor sources produce allergenic particles, including the feces of dust mites which are minute creatures which feed on the dead skin which we shed every day, and the feces of cockroaches, the dander from animals, especially vermin, pollens from flowering plants. About 15 million Americans are allergic to dust mite feces and up to 65% of people may be allergic to cockroach feces. Studies of allergies to animal dander show that about 10% of people develop allergies to dogs, about 13 % to cats, 37% to mice, and around 57% to rats. The number of people with allergies is increasing and this may be because of the effects of other air pollutants on the lungs. Most people who develop allergies to animal dander will do so within 1 month to 3 years, although the sensitization period ranges from a few days to 22 years. Allergenic particles become airborne when a surface is disturbed, such as happens when a carpet is vacuumed or a mattress is bounced on, and inhalation of these particles produces an allergic reaction in the person.

Studies of office carpet dust have found up to 30 dust mites per gram of dust (about 850 mites per ounce of carpet dust) and up to 200 mites per gram of dust from office chairs (about 5,700 mites per ounce of chair dust). Several research studies have found that allergenic dust correlates with many symptoms of the sick building syndrome, especially the eye, nose, and throat irritation symptoms. Thorough office cleaning also has been shown to reduce sick building syndrome complaints by up to 50%.


Go to the next lecture