Legionella E-news | 17 January 2002 | Matthew Freije, Editor
© Copyright 2002, HC Information Resources Inc.

Responding to a Legionnaires' Disease Outbreak in an Industrial Plant: A Case Study

by Matthew Freije and Scott Burgoon

Editor’s note: In his Master’s thesis, “Legionnaires' Disease: Lessons for Industry,” Scott Burgoon, Senior Industrial Hygienist with General Physics Corp., details incidents in five industrial plants--a meat packing plant, a power plant, and three plastic injection molding plants--in which exposure to Legionella was either suspected or confirmed. This article focuses on one of the injection molding plant outbreaks, highlighting management’s response to the situation, and OSHA’s response to management. The information is based on Maryland Occupational Safety and Health Administration (MOSH) Case Files. Many thanks to Scott for sharing his work.

Legionella contamination had not been suspected in a plastic injection molding plant in Maryland (USA) until one of the employees died of what was reported as Legionnaires’ disease. On 2 October 1998, the very same day the death was reported to the Baltimore City Health Department, the plant management initiated an investigation. They hired a consultant and sought help from Johns Hopkins Hospital.

Five days later, on 7 October, the Maryland Occupational Safety and Health Administration (MOSH), acting in an advisory capacity to the Maryland Department of Health and Mental Hygiene (DHMH), initiated its own investigation. Around this time six additional cases of pneumonia were diagnosed in plant employees, five of which were eventually confirmed as Legionnaires’ disease. The plant management shut down the facility and treated the water systems.

Investigators estimated that exposures occurred during the first half of September. The epidemiologic investigation revealed no common exposures to employees outside the plant, so the plant was considered the likely source of contamination. However, by the time Legionella was suspected, the patients had already begun aggressive antibiotic treatment, so diagnostic tests were inconclusive. Although Legionella was found in environmental samples, the strains could not be linked to the affected employees.

The plant manufactures plastic enclosures (e.g., caps, lids) by the injection molding process, which utilizes water to cool molds and finished product. Although water systems that cool molds are technically closed systems, exposure to water spray can occur when changing molds or temperature control equipment. In addition to the potable water system, the plant has six non-potable systems that were used for injection molding and air conditioning. The plant has two sections, East and West; the Legionnaires’ cases occurred only in the East section.

DHMH collected 74 environmental samples from both potable and non-potable water systems. Three separate laboratories that initially analyzed the samples reported negative results for all 74 samples. Subsequently, however, 6 of the 74 samples were sent to a fourth laboratory that did find Legionella (LpSg's 1, 5, and 6). In fact, 5 of the 6 retested samples were positive.

All the positive samples were collected from the cooling systems. The concentrations ranged from 30 to 3,510 cfu/ml, but DHMH considered the counts unreliable because of the processing delay. The sixth retested sample, collected from a water mist machine, tested negative. No samples from potable systems were retested (in hindsight this would appear to be a mistake).

Investigators discovered that two sodium hypochlorite drums used for two cooling systems had been empty for six weeks, ever since the water treatment company’s last service call on 3 August 1998. A chemical feed pump had apparently malfunctioned, emptying the drums more quickly than normal.

The investigators could not confirm the source of contamination but suspected one of two scenarios. The first scenario was that cooling water that dumps into an open sump had become aerosolized and then distributed by the ventilation system. Legionella pneumophila was found in water collected from the sump at the high (but possibly inaccurate due to extended holding time) concentration of 3,510 cfu/ml.

Another possibility, deemed less likely by investigators, was that Legionella-contaminated aerosols were blown from the rooftop cooling tower down the side of the building to the employee smoking area. Legionella (80 cfu/ml) was found in the cooling tower, and all infected employees were smokers who worked in the East building.

DHMH made the following recommendations, which the plant implemented immediately:

Instruct all employees to report illnesses to the company’s human resources department.
Report all respiratory illnesses to DHMH daily.
Provide all employees and their physicians with a Legionella fact sheet.
Continue voluntary closure of the East building pending results of the environmental tests and development of an action plan.
Do not move East building employees to the West building (to assist in the epidemiologic investigation).
Provide environmental test results to DHMH as soon as they are available.
Coordinate press inquiries through the DHMH Public Relations department.

In 1997, the US Department of Labor, Occupational Safety & Health Administration (OSHA) fined a Cincinnati injection molding facility following an investigation of three Legionnaires’ cases (no deaths) among its employees. OSHA cited Section 5(a)(1) of the 1970 Occupational Safety and Health Act, commonly referred to as the “General Duty Clause,” which is a catch-all standard requiring employers to maintain a workplace free from recognized hazards that could cause death or serious physical harm. OSHA stated that the Cincinnati plant employees were exposed to excessive levels of legionellae during injection mold setting and changing, quality laboratory parts testing, and equipment repair or maintenance, and that these exposures could have caused Legionellosis.

In contrast, the Maryland plant was not fined for the 1998 outbreak even though it was more severe than the Cincinnati outbreak in terms of cases and deaths. The agencies’ decisions to fine or not to fine were apparently based in large part on plant managements’ prevention efforts and cooperation. Before the outbreaks, the Maryland plant had attempted to properly treat its cooling water systems and monitor bacteria counts, but the Cincinnati plant had not done so even though cases of respiratory illness had been reported among its employees three years prior. After the illnesses were reported, the Maryland plant voluntarily initiated its own investigation and closed the plant, but the Cincinnati plant did not. Throughout the investigation, the Maryland plant cooperated fully with health officials, implementing all recommendations immediately, but the Cincinnati plant did not.

Here are specific factors considered by MOSH in not fining the Maryland plant:

1. The company had an industry accepted water treatment program in place.

2. There was no indication of previous employee illnesses from the water systems.

3. The company took immediate action to protect its employees by notifying local health and medical officials as soon as a problem was suspected, and by hiring a consultant to assist in the evaluation.

4. The company voluntarily closed the suspected section of the plant.

5. The company cooperated fully with health, medical, and regulatory authorities.

6. The company implemented measures that exceeded those typically recommended when dealing with a suspected Legionnaires’ outbreak.

7. The company increased the frequency of its biocide treatment and changed to another biocide.

In sum, although the Maryland plant did not take all appropriate Legionella-preventive measures in its water systems, it attempted to properly treat its cooling systems, and, after a case of Legionnaires’ was identified, it immediately initiated an investigation, took steps to protect employees, and cooperated fully with health authorities. In doing so the plant avoided regulatory citations. What we don’t know is how the plant fared against lawsuits that may have been filed on behalf of the employees who contracted Legionnaires’, claiming the illnesses could have been prevented if the plant had made a reasonably diligent effort to control legionellae in its systems and had tested the water to see if its control measures were working.