Planning Investigations in Healthcare Facilities

Key points

  • How health department investigators respond to healthcare-associated cases and outbreaks of Legionnaires' disease depends on many factors.
  • The guidance below addresses when CDC recommends a full investigation and details the steps involved.
  • This information supplements the considerations for all types of facilities with details specific to healthcare facilities.


Factors that can impact an investigation in a healthcare-associated case or outbreak include:

  • Type and size of the healthcare facility
  • Existing capacity of the facility and health department
  • Number of cases
  • Water management program performance
  • Routine environmental sampling results

Potential points of contact

Public health personnel should work closely with healthcare facility staff at each step in the process. The appropriate healthcare facility point of contact may vary, depending upon the step. Contacts can include:

  • Administrator
  • Engineer
  • Facility manager
  • Healthcare provider
  • Infection preventionist
  • Quality assurance representative

Determine if a full investigation is needed

CDC recommends a full public health outbreak investigation for the source of Legionella in a facility upon identification of:

  • ≥1 case of presumptive healthcare-associated Legionnaires' disease at any time
  • ≥2 cases of possible healthcare-associated Legionnaires' disease within 12 months of each other

Meeting one of these criteria raises concern regarding the potential for ongoing transmission of Legionella to others.

With only a single possible healthcare-associated case, available epidemiologic evidence may not be strong enough to warrant a full investigation.

The terms "outbreak investigation" and "full investigation" are used interchangeably. The steps of an outbreak investigation are the same for a full investigation in response to a single presumptive healthcare-associated case.

Timeframe considerations

The 12-month timeframe for outbreak detection is intended to be sensitive enough to capture outbreaks involving potable water. Potable water is a term for water used for drinking and bathing. Potable water outbreaks tend to have a low attack rate with cases spread out over a prolonged period.

The longer timeframe also helps account for periodic changes in risk (e.g., due to seasonality). Note that under certain circumstances, the timeframe under consideration may be shorter, such as during cooling tower outbreaks. These outbreaks tend to be more explosive and shorter.

Considerations for an environmental assessment

Even if public health personnel determine that a full investigation isn't warranted, consider conducting an environmental assessment. Public health personnel can also recommend that healthcare facility staff conduct an environmental assessment.

An environmental assessment can help determine if conditions for Legionella growth exist in the building water system(s). This also provides an opportunity to stress the importance of surveillance and prevention measures to healthcare facility staff.

These additional steps might be particularly useful if the facility has one or more of the following characteristics:

  • Previously been associated with Legionnaires' disease
  • Recently identified Legionella in the facility's water system(s)
  • Had a recent disruption of the facility's water system(s)
  • Nearby buildings have been associated with Legionnaires' disease

Steps involved in a full investigation

Once public health personnel determine the need for a full investigation, there's a series of steps that should take place.

Reminder: The following information is intended to supplement, not replace, the steps outlined for all types of facilities.

Collect case information

Work with healthcare facility staff to conduct active case surveillance to identify new and recent patients with pneumonia.

Test clinical specimens

Test identified pneumonia patients for Legionella using preferred diagnostic tests.

Take steps to prevent additional exposures

Consider removing aerosolizing devices that aren't necessary for the function of the healthcare facility. Examples include decorative fountains and waterfalls.

Per ASHRAE Guideline 12, decorative fountains shouldn't be in areas or buildings frequented by people at increased risk for Legionnaires' disease1. This would include healthcare facilities.