Case Verification

When public health officials receive a report of a case of Legionnaires’ disease, these officials should first verify that the case meets the case definition for legionellosis.

Standard Case Report Form

After verifying the case, public health officials should interview the patient about the 10* days before onset of symptoms to capture, at a minimum, key demographic, clinical, exposure, and reporting details for surveillance purposes using the Supplemental Legionnaires’ Disease Surveillance System (SLDSS) Legionellosis Case Report Form pdf icon[2 pages], or equivalent state-specific case report form.

See How to Report Cases and CDC Legionellosis Case Report Form Instructions for additional information.


* The incubation period for Legionnaires’ disease is most commonly 2 to 10 days from the time of exposure to symptom onset, with an average of 5 to 6 days1, but public health officials have reported incubation periods up to 26 days under rare circumstances2. For surveillance purposes, public health officials collect exposure histories for the 10 days before date of symptom onset. However, in outbreak settings where it is important to consider a wide range of possible sources, use of a 14-day range (or more) may be desirable.


  1. Egan JR, Hall IM, Lemon DJ, Leach S. Modeling Legionnaires’ disease outbreaks: Estimating the timing of an aerosolized release using symptom-onset datesexternal icon. Epidemiology. 2011;22(2):188–98.
  2. Fraser DW, Tsai TR, Orenstein W, et al. Legionnaires’ disease: Description of an epidemic of pneumoniaexternal icon. N Engl J Med. 1977;297(22):1189–97.