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Legionnaires' Disease

Section III:B. Investigation Protocols: Level Two

Medical SurveillanceInitiate a level two investigation when more than one possible cases of Legionnaires' disease has been reported at a facility. A level two investigation is similar to a level one investigation with the addition of the following procedures. Local Health Authorities, Centers for Disease Control and Prevention (CDC) investigators, or OSHA representatives will:
  • Inform and educate employees about the disease to minimize employee concerns and aid in early recognition of new cases.

  • Conduct medical surveillance of all employees currently on sick leave to identify any new cases.

  • Assess past sick-leave absences for undetected cases of the disease.

  • Collect water samples during the walkthrough inspection.
Local, state, or federal authorities will take the following steps when more than one probable case of Legionnaires' disease has been reported:
  1. Obtain an overview of all water systems (Section II:A. Level One)
  2. Conduct a walkthrough inspection and collect water samples
  3. Initiate an employee awareness program
  4. Review worker absences to detect other cases
  5. Recommend control actions (Section II:A. Level One)

TopStep 2: Walkthrough inspection with sample collection
Fig. 1: Collect water samples during the walk through.
Fig. 1: Collect water samples during the walk through.
Conduct a walk through survey of the facility and collect water samples.
  • Estimate the size of the building and the number of water services during an initial walkthrough.

  • Prearrange supply and shipping of the required number of sterile sample containers with the appropriate laboratory.

  • See Section II:E. Water Sampling Guidelines for sampling procedures.


TopStep 3: Initiate an employee awareness program
Fig. 2: Employee Surveys
Fig. 2: Employee Surveys
The purpose of an employee awareness program is to inform the workers of the potential outbreak and to educate them about Legionnaires' disease. Implement the following elements of this program immediately upon recognition of more than one probable or confirmed case of disease in the workplace.
  • An initial employee training session that provides basic information about the disease and actions being taken to investigate the problem.

  • An ongoing general information service to provide updates and answer questions that may arise among employees.

  • Medical and psychological counseling services when an outbreak has occurred.

  • A medical monitoring program should be instituted to track all workers currently on sick leave.


TopStep 4: Review worker absences to detect other cases
Case Identification Program: The purpose of this phase of an investigation is to identify cases of Legionnaires' disease among the workers. The investigation includes identification of all employees who took three or more consecutive days of sick leave from six weeks before the index Legionnaires' case was identified to the present. Request that all employees who have been identified as having had pneumonia, or potentially having had pneumonia, during this period undergo voluntary medical testing to detect evidence of Legionnaires' disease. A physician's diagnosis of pneumonia or pneumonia-like symptoms that includes a fever (38C, 101°F) and cough indicate a need for further evaluation. A sample program is described below.

1. Conduct an Interview: Examine sick leave records to identify all employees who used three or more consecutive days of sick leave from six weeks before the earliest known case to the present. 2. Medical Release: Request employees who experienced a pneumonia-like illness and saw a physician to sign a medical release form to allow the company or OSHA to obtain additional information from the attending physician.
    Fig. 3: Employees with symptoms should fill out proper recordkeeping forms.
    Fig. 3: Employees with symptoms should fill out proper recordkeeping forms.
  • Interview the physicians of all employees who have sought medical care and signed a medical release form using a physician survey questionnaire.
    Appendix III:B-5. Physician Survey Questionnaire - Legionellosis

  • Inform employees participating in surveys of their Privacy Act rights as well as their right to protect their own medical information.

    • Physician-patient confidentiality should not be violated.

    • Necessary medical information may be communicated only with the patient's written permission.

    • When seeking employees' permission, clearly inform them that the purpose of obtaining a proper diagnosis and sharing this information is to protect them and their fellow workers against the potential threat of legionellosis.
  • Handle all medical records in accordance with 29 CFR 1913.10.

    • It may be necessary to obtain medical releases from the employees interviewed to obtain supplemental information from a company health unit or from the employee's physician.

    • Seek similar arrangements for permanent contract employees controlled by separate organizations in the building such as janitors, cafeteria workers, and security personnel.
3. Clinical Testing: Consider a clinical test for potential cases to confirm additional cases. Recommend a serological or other diagnostic test for possible Legionnaires' disease cases identified from interviews, the review of work absences, and discussions with the patients' physicians.
  • Serological tests determine the antibody level of an individual.

  • A single antibody titer of 1:256 with a physician's diagnosis of pneumonia should be interpreted as a probable case of Legionnaires' disease.

  • If an antibody titer for Legionnaires' disease Bacteria (LDB) was obtained at the time of illness or if serum was collected from the patient at the early phase of the illness (acute phase), then the acute antibody titer level should be compared with the convalescent titer. A four-fold increase in titer is sufficient to confirm a case of Legionnaires' disease.

  • Additional information (App I:B) on diagnostic methods, including culture, direct fluorescent antibody (DFA) staining, and serology is also available.
4. Other diagnostic tests may also be appropriate:
  • If the potential case occurred recently, a urine antigen test may detect L. pneumophila serogroup-1 antigen.

    • A positive urine antigen test for a diagnosed pneumonia case is also accepted as evidence of a confirmed case. However, this test is available only for L. pneumophila serogroup-1 infections.
  • Collect sputum, lung tissue, or lung aspirates from currently symptomatic individuals for LDB culture.

    • A positive culture confirms the diagnosis of Legionnaires' disease.
5. Disease Confirmation: If this process confirms more than one case of disease, then the facility should be considered to have experienced an outbreak. See Section IV. Outbreak Response. Note: The immediacy of the action will depend on whether the outbreak is ongoing or occurred 30 days or more in the past.
  • Take prompt action to control exposure at the site if there is evidence that an outbreak is on-going.

  • Initiate control procedures, continue medical surveillance of the workforce to detect new cases of disease, and identify the water source responsible for the outbreak.
6. Assess the Results: Use the walkthrough inspection, medical surveillance, and water test results to determine a course of action.
  • If the evidence indicates that two or more cases of Legionnaires' disease have occurred at a site and at least one of the cases was within the last 30 days, assume that an outbreak is in progress.

  • Take prompt actions as required in Section IV to protect building occupants.

  • If the water system is poorly maintained or operating temperatures for water heaters are below 60C (140F), or cold water above 20C (68F), recommend corrective actions.
No action is necessary if the results of the investigation are negative. Under the following circumstances, assume that the site is not the origin of the identified cases:
  • All water and HVAC systems are well maintained and in good operating condition.

  • All water sample results are negative or acceptably low.

  • No new cases of the disease have been identified at the work site.

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