Week 4 - Legionellosis

Question 1

What is Legionellosis?

Answer 1

Gram-negative bacillus
* Intracellular parasite of
free-living protozoa primarily found
in freshwater
* More than 60 species
* L. pneumophila: ~90% of reported US cases 13
1 Fields BS et al. Clin Microbiol Rev. 2002;15(3):506–26.

Question 2

What factors lead to Legionella growth? and how are they contracted?

Answer 2

Internal and external factors can lead to Legionella growth in building water systems

Legionella grows best in large, complex water systems that are not adequately maintained

Susceptible people contract Legionnaires’ disease by inhaling aerosolized water droplets or by aspiration of drinking water containing the bacteria

Question 3

What are risk factors for for Legionnaires’ disease?

Answer 3

• Age ≥50 years
• Smoking (current or historical)
• Chronic lung disease (e.g., emphysema or COPD)
• Immune system disorders due to disease or medication
• Systemic malignancy
• Underlying illness (e.g., diabetes, renal failure, or hepatic failure)

Question 4

Who does the state health department report legionella to?

Answer 4

• National Notifiable Disease Surveillance System (NNDSS)
• Supplemental Legionnaires’ Disease Surveillance System (SLDSS)
• National Outbreak Reporting System (NORS)

Question 5

What are the Unique Aspects of Legionellosis Outbreaks?

Answer 5

Outbreaks commonly involve only a handful of Legionnaires’ disease cases

• Low attack rate (<5%)
• Tip of the iceberg (diagnosing and reporting cases)

Requires finding the environmental source and eliminating it to prevent others from being exposed

• Environmental component

Requires specialized lab testing

• Culture of clinical and environmental specimens

Question 6

What are the Steps to Investigating an Outbreak?

Answer 6

Identify the outbreak and determine the level of public health response
needed
* Develop a questionnaire and interview case patients for water exposures
and intrinsic risk factors
* Conduct additional case finding
* Conduct an environmental assessment to evaluate potential environmental
exposures
* Create a sampling plan and collect water samples for Legionella culture
* Compare environmental and clinical isolates
* Determine plan for remediation

Question 7

What are common outbreak setting?

Answer 7

Hospitals
* Long term care facilities
* Hotels
* Cruise ships
* Community