Looking for Additional Healthcare-associated Cases

Key points

  • It's important to identify additional cases as part of a Legionnaires' disease investigation in a healthcare facility.
  • Investigators should assess routine practices, review medical and laboratory records, and consider other data.

Conducting additional case finding

Looking for patients with Legionnaires' disease with healthcare exposures is an important part of a healthcare-associated outbreak investigation.

To find cases, investigators should:

  • Assess routine practices
  • Perform a retrospective chart review
  • Review laboratory records
  • Consider other data

Assess routine practices

Determine if the facility routinely conducts surveillance for healthcare-associated pneumonia.

Determine if the facility tests any identified patients for Legionella. If so, what tests does the facility use?

Perform a retrospective chart review

Look at patient charts for the past 12 months to identify pneumonia cases that could've been healthcare-associated. If additional cases are identified, determine if patients were tested for Legionella.

Review facility laboratory records

Include all Legionella testing and any positive results in this review.

Consider also reviewing laboratory records for other healthcare facilities in the same catchment area. Look specifically for patients recently discharged from the healthcare facility of concern.

Consider other data

Consider evaluating trends in infections due to other water-related pathogens. Specific pathogens could include nontuberculous mycobacteria and the following gram-negative bacteria1:

  • Pseudomonas
  • Burkholderia
  • Stenotrophomonas

This step may help investigators evaluate the facility's water management program.

Also consider available syndromic surveillance. These data can serve as an early warning system for public health concerns including Legionnaires' disease.

CDC's Line List Template is a helpful tool to summarize case demographic, clinical, and exposure information specific to a healthcare-associated outbreak.

CDC's Legionnaires' Disease Medical Record Abstraction Form Template may also assist with record review for healthcare facility investigations.

Conducting active clinical surveillance


Active clinical surveillance is a period of enhanced surveillance. Healthcare facility staff proactively and systematically identify patients with healthcare-associated pneumonia (pneumonia with onset ≥48 hours after admission2).

During this time, they also ensure that healthcare providers perform Legionella-specific testing for each of those patients. It's crucial for detecting additional cases of healthcare-associated Legionnaires' disease in a healthcare facility.


Options for identifying patients with healthcare-associated pneumonia diagnoses could include a daily review of:

  • Chest radiographs and CT scans ordered to diagnose pneumonia
  • New pneumonia diagnoses occurring in patients in intensive care units
  • Laboratory testing ordered to diagnose pneumonia

These laboratory tests could include sputum Gram stain and culture.


After identifying cases of healthcare-associated pneumonia, healthcare facility staff should perform Legionella testing. Healthcare facilities should retain clinical specimens for the duration of the investigation.


Per Healthcare Infection Control Practices Advisory Committee guidance, active clinical surveillance should continue for at least 2 months once initiated.

Many public health jurisdictions will recommend active clinical surveillance for up to 6 months or longer. It depends on many factors including identification of additional cases or concerns regarding performance of the water management program.