December 9, 1998

Workers engaged in the manufacture of plastic parts using injection molding equipment may be at an increased risk for Legionnaires' Disease, a potentially life-threatening form of pneumonia. Legionnaires' Disease may be contracted by exposure and inhalation to water and water mists containing elevated concentrations of Legionella and Legionella Pneumophila (LP). These organisms have been found in the water used to cool the metal molds and the process equipment used during the manufacture of plastic parts.

During a Cincinnati Area Office investigation, described below, high concentrations of LP were detected in the water used to cool metal molds and the process equipment at a plastic injection molding facility, and unconfirmed cases of Legionnaires' Disease were identified among the workers. At the time of this writing, a Legionnaires' Disease outbreak has been reported in a Baltimore, Maryland area plastic injection molding facility. Five employees have been confirmed to have developed Legionnaires' Disease, and one of the workers has died (Three other cases of pneumonia were identified. Although the initial laboratory evaluation of these cases did not confirm Legionnaires' Disease, additional antibody testing is being pursued. Legionella Pneumophila has been isolated from non-potable water samples collected at the facility. The Maryland Occupational Safety and Health program (MOSH) is still conducting an investigation). In addition to these cases, a fatal case of Legionnaires' Disease involving plastic injection molding operations has been described in the industrial hygiene industry literature⁽²⁾. In that report, two workers employed in the plastic injection molding industry contracted pneumonia and one of the individuals later died. Water sample results indicated that high concentrations of LP organisms [3,000 colony forming units (CFU)/milliliter] were detected in the chilled water used to cool the molds. The fatal case was confirmed to have had Legionnaires' Disease when a positive culture taken from the victim identified the organism as Legionella Pneumophila.

The Centers for Disease Control and Prevention (CDC) has a set of confirmation criteria to establish the diagnosis of disease caused by Legionella. Inconclusive test results for Legionnaires' Disease (as was the case in the Cincinnati investigation) are common. Furthermore, the diagnosis may be delayed because of atypical symptoms or a low index of suspicion on the part of treating physicians. Consequently, as might be expected, Legionnaires' Disease often goes largely undetected. Although only about 700 cases of the disease are reported to CDC annually, the number of cases which are contracted in the community and which require hospitalization has been conservatively estimated by CDC at 11,000 cases per year in the US.⁽³⁾ This estimate excludes nosocomial (hospital-acquired) cases and institutionalized (nursing home) cases. Since many cases do not result in hospitalization and the disease is poorly diagnosed, the actual number of cases which occur in the U.S. annually is not known and estimates from other groups vary widely.

The plastic injection molding process utilizes several water sources for cooling purposes such as chilled water from a mechanical refrigeration unit or cooled water supplied directly from a cooling tower. The water may be delivered at relatively high pressure (80 psi), thus enhancing the potential for aerosolizing the water into the workplace in the event of leaking lines or during mold change outs. These water sources can present a hazard if operating conditions do not minimize the growth of LP in the water.

The Cincinnati facility used a chilled water system to cool the molds, and a cooling tower water system to provide cooling water for removal of the heat generated from hydraulically-operated pneumatics of the injection molding equipment. High concentrations of LP were detected in the chilled water system using polymerase chain reaction (PCR). Water samples, which were at a temperature of 99°F, were collected from the outlet of the mold and contained over 1,000 organisms of LP per mL. Concentrations of LP measured in two separate chilled water storage tanks ranged from 250 to 1,000 organisms per mL. These chilled water systems were not treated with any biocides, possibly because of the mistaken notion that the reduced temperature (50°F) of the water in this closed loop would not allow for the growth of bio-organisms. Unfortunately, the growth of LP occurred as a biofilm in areas of the mold where the water temperature approached the ideal growth temperature, and these organisms then contaminated the cool water storage upon return of the water to the chilled water storage tank.

When tested by PCR, water samples from the Cincinnati facility collected from the cooling tower (which was poorly maintained, but which had received some biocide treatment) indicated the presence of high concentrations of Legionella genus bacteria or Legionella-like bacteria (in excess of 1,000 organisms per mL), but low concentrations of LP (approximately 10 organisms per mL). Because other species of Legionella, in addition to LP, are capable of causing Legionnaires' Disease and other respiratory illnesses, exposure to this water source also presented a health risk.

To reduce the possibility of plastic injection molding workers contracting Legionnaires' Disease, it is recommended that plastic injection molding manufacturers follow good industry practices to minimize the potential for proliferation of these organisms in water systems. Therefore, as a preventive measure, it is important to initiate environmental evaluations of plastic injection molding facilities. A general overview of good practice is provided in the OSHA Technical Manual Chapter on Legionnaires' Disease. Additionally, the Cooling Tower Institute⁽⁴⁾ has recently issued guidelines for control of Legionella in cooling tower and evaporative condensers. Unfortunately, based on the current body of information for control of Legionella, adherence to industry practice cannot in itself provide adequate assurance that Legionella proliferation in a water system will not occur. Recently, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) recognized water sampling as the only method of verifying effective maintenance on cooling towers⁽⁵⁾. Presently, it is strongly advised that water sampling be conducted for Legionella organisms to verify that the operating and maintenance practices are working effectively. Guidance on water sampling is also provided in the OSHA Chapter on Legionnaire's Disease.

In general, good practice recommendations include:

• Periodic cleaning and disinfecting of the cooling towers as described in the Wisconsin Protocol⁽⁶⁾
• Frequent visual inspection and periodic maintenance of the water system and its mechanical components.
• Use of alternating biocides, one of which is an oxidizing-type, to prevent the proliferation of the organism in the water during operation. Active forms of chlorine, bromine, or organic chemicals which release active chlorine or bromine are often alternated with other types of biocides.
• Proper control of pH. Alkaline pH (high) conditions reduce the efficacy of both chlorine and bromine as biocidal agents, although bromine is more tolerant of high pH than chlorine.
• Proper control of dissolved solids and the minimization of organic material in the water. Organic based materials such as decaying leaves and other organic matter will consume the oxidizing capability of the biocides resulting in insufficient bacterial control.

In addition to good maintenance and operating practices, systems designed to operate with low sump or basin water temperature will also reduce the potential for bacterial growth. Properly sizing the cooling tower ensures that the system has adequate cooling capacity to meet heat removal demands. Insufficient cooling capacity will result in warmer water temperatures in the cooling tower, a condition which encourages the growth of LP.

Control of the amount of water mist, or drift, is also an important design feature for cooling towers. Drift eliminators installed prior to the exhaust of a cooling tower will reduce the amount of aerosolized water lost to the environment and also reduce the risk of infection if this water source is contaminated with Legionella.

Please distribute this bulletin to all area offices and appropriate labor and industry groups.