Hypersensitivity Pneumonitis (HP)

January, 2001: Two members of Local Union 1939 find themselves in the intensive care unit suffering from a mysterious lung disease. Before the year ends, 105 of their co-workers will be placed on work restrictions, and 37 of these will remain on medical leave due to respiratory problems. A total of 12 workers would eventually be diagnosed with hypersensitivity pneumonitis, the ailment first seen twelve months earlier.

What Is Hypersensitivity Pneumonitis?
HP is an inflammation in and around the air sacs of the lung caused by an allergic reaction to inhaled organic dusts or chemicals. Substances that cause allergies are called antigens. When the body recognizes these antigens, it creates special proteins to attack and neutralize the invading substance. In addition to producing proteins, the body reacts by swelling the site with fluid. It is believed that many substances can cause allergic reactions in the lungs. Organic dusts that contain microorganisms or proteins as well as chemicals such as isocyanates may cause HP. Picure (below, left) shows an x-ray of lungs with hypersensitivity pneumonitis.

While microorganisms may cause this disease, HP is not an infection like pneumonia, but an allergy. You cannot catch HP from another person. Generally, a person must be exposed to allergies frequently over many weeks before sensitivity and disease develop. If a person has developed HP, and they continue to have allergic reactions, scars may form in the lungs. This is called pulmonary fibrosis. Shortness of breath during exercise, coughing up sputum, tiredness, and weight loss get worse and eventually the disease may lead to respiratory failure. Machinists are not the only workers who may suffer from HP. Farmers, wool sorters, bird handlers, and chemical workers may develop the disease. Asthma bronchitis and daily lung function drops occur with exposure to MWF in the absence of HP problems.

What Causes HP in UAW members?
In response to 8 clusters of HP in automotive plants and small parts plants using metalworking fluids (see Table 1), the UAW Health and Safety Department asked the National Institute for Occupational Safety and Health (NIOSH) to assist in identifying the cause of this disease among our members. The UAW-Chrysler National Joint Committee on Occupational Safety and Health sponsored a gathering of labor and management health and safety officials and outside experts in 1996. This group concluded that the risks were greatest where water-based fluids were used, and where unusual microbes are present.

Hypersentivity Outbreaks in 1996 Workshop
PLANT	YEAR	HP CASES	MYCOBACTERIA	FUNGI?
1	1992	9	Y	Y
2	1994-95	3	?	Y
3	1994-95	2	Y	?
4	1995-96	34	Y	Y
5	1993-97	13	Y	Y
6	1994-97	10	N	Y
7	1991-95	13	N	Y
8	1992-97	14	?	Y
This chart hints at the difficulty in determining the specific culprit in metal working fluid HP cases. The lesson is not to rely on a single test when looking for microbes. Also beware of newly discovered threats like mycobacteria.

 

Figure 2. Scanning Electron Micrograph of Mycobacteria chelonae (photo by Janice Carr, Center for Disease Control)

The paper summarizing the conference states “Mycobacteria chelonae were found in four of eight plants. In two plants, mycobacteria cultures were performed and none detected, suggesting other Mycobacteria flora may be implicated”*. Since that time, the case against Mycobacteria is getting stronger. In more recent outbreaks a new species has been identified and given the name, Mycobacteria immunogen. While we can’t be 100% sure that Mycobacteria are the only cause, it is well known that certain components of their cell structure have been shown to heighten the immune response. Thus, efforts to remove these contaminants from the coolant and inhibit their growth should lessen the risk of developing HP.

How can HP be prevented?
Two simple steps can prevent HP in your plant: first, keep the fluid as clean as possible, and second, minimize breathing the mist that is generated. Microbial growth can be minimized by using clean water to make up solutions, keeping the fluid aerated, keeping dirt and debris out, preventing microbial overgrowth using biocides, and removing biofilm (slime) by cleaning when fluids are replaced. Testing the fluids is a good way to ensure cleanliness. Test kits are available to ensure that preventive maintenance is done properly.

The best way to avoid exposure to metalworking fluid mists is to enclose the operations, exhaust them outdoors, and provide an adequate supply of fresh air close to workstations.

Mycobacteria survive by eating dead or decayed organic matter. No one has been able to grow them in clean metalworking fluids. Biocides should only be used to prevent bacterial growth. Once the fluids have become grossly contaminated, use of a biocide to “correct’ the problem means little more than preparing dinner for the really bad actors.

The best way to avoid exposure to metalworking fluid mists is to enclose the operations, exhaust them outdoors, and provide an adequate supply of fresh air close to workstations. NIOSH recommends that exposures be limited to 0.5 mg/m3 (1/10 of the current legal limit!).

How are metal working fluids tested?

Figure 3. A commercial test kit These slides are dipped into metalworking fluids and incubated for 24 hours. They give a good estimate of bacteria count, but don’t work well for mycobacteria

Most plants only monitor the concentration and pH (acidity) of water-based metalworking fluids. Some measure the amount of tramp oil (hydraulic and other oils that leak into the system). High levels of tramp oil indicate a need for machine maintenance and may provide a breeding ground for certain obnoxious bacteria. Other plants use dip slides (see Figure 3). These slides are coated with a gel which allows bacteria and fungi to grow. The slides are dipped into the coolant and incubated for 24 hours. They can give a good indication of the amount of bacteria living in the fluid. Ask to see the test results – any bacteria counts over 106 colony forming units/milliliter or any fungus is a sign of a problem. Unfortunately, Mycobacteria don’t grow well on these slides. A more expensive test, is needed to determine the presence of Mycobacteria.

How is HP diagnosed and treated?
Your doctor should ask you questions about your job. Some of the test she might use to diagnose HP include a chest x-ray taken, a pulmonary function test, and tests to determine the amount of oxygen your blood is carrying. You may be referred to a pulmonologist, who might run tests for antibodies in your blood, perform a lung CT scan, or even do a lung biopsy.

Removal from the offending agent is the most likely therapy. Oftentimes corticosteroids are prescribed to reduce the symptoms and minimize the inflammation. In severe cases, supplemental oxygen therapy may be recommended. If your doctor authorizes your return to work, be sure to tell him if any of your symptoms recur.

What if someone contracts HP?
If someone in your local contracts HP steps should be taken immediately to control exposure so others don’t get sick. Experience in other plants indicates that the key to controlling an HP outbreak is improved ventilation starting immediately with general air handling. Prompt draining and cleaning of the affected coolant systems will also help. After recharging the system with new coolant an improved fluid management program is a must. Part of this program includes the use of an effective biocide. Phenolic biocides are reportedly effective in control of Mycobacteria but may have chemical toxicity. Regardless of which biocide is selected, the concentration of the biocide needs to be monitored on a regular basis.

Next: Summary of Control Measures

*Kreiss, Kathleen, Cox-Gansen, Jean (1997): Metalworking Fluid—Assocated Hypersensivty Pnemonitis: A workshop Summary. American Journal of Industrial Medicine 32:423-432.