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CDC Surveillance Classifications

Exposure Categories for Surveillance Purposes

“Confirmed” and “suspect” are CSTE surveillance case classifications, based on type of laboratory confirmation.

“Definite” and “possible” are healthcare exposure case classifications and can apply to both confirmed and suspect cases.

  • Travel: the patient spent at least one night away from home (in the state of residence, another state, or another country) in the 10 days before date of symptom onset, not including nights spent in a healthcare facility
  • Definite healthcare: the patient spent the entire 10 days before date of symptom onset in a healthcare facility
  • Possible healthcare: the patient spent a portion of the 10 days before date of symptom onset in a healthcare facility
  • Assisted living: the patient spent a portion of the 10 days before date of symptom onset in a facility that provides custodial care without skilled nursing (e.g., assistance with activities of daily living, like bathing and dressing)
  • Senior living: the patient spent a portion of the 10 days before date of symptom onset in a facility that provides independent living for the elderly

Note: Patients can have both travel and healthcare exposures in the 10 days before date of symptom onset. The CDC Legionellosis Case Report Form [2 pages] provides space to indicate multiple exposures.

 

Goals of Surveillance

  • Monitor and describe incidence and trends
  • Rapidly recognize cases that occur in similar locations or with similar exposures to detect outbreaks
  • Understand risk factors for infection
  • Identify opportunities for control and prevention
  • Monitor effectiveness of interventions implemented as part of an outbreak investigation

 

Public Health Impact

Outbreaks of Legionnaires’ disease can be difficult to detect because of:

  • Low attack rate
  • Time interval between exposure and symptom onset
  • Dispersal of people from the source of the outbreak
  • Underdiagnosis of cases

Strong surveillance helps to quickly identify new cases, epidemiological links between cases, and the need for outbreak investigations. Such investigations are critical for detecting sources of transmission and implementing control measures. While state and local public health officials are best positioned to systematically track Legionnaires’ disease cases and efficiently detect outbreaks within their respective jurisdictions, CDC is uniquely positioned to establish connections between cases that occur among residents of different jurisdictions. Most cases of Legionnaires’ disease are not associated with a known outbreak.1 However, improved ascertainment and reporting of exposure information helps identify possible sources of exposure to other susceptible people and can increase detection of outbreaks.

 

Footnote

  1. Hicks LA, Garrison LE, Nelson GE, Hampton LM. Legionellosis — United States, 2000–2009. MMWR Morb Mortal Wkly Rep. 2011;60(32):1083–6.
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