Table 4 Risk of Pontiac fever according to Legionella concentrations measured by fluorescent in situ hybridization (FISH) technique on the shower aerosol samples collected by liquid impaction
Exposure scenariosConcentration (per l air)*Cases or PF-like eventsPerson–daysRR (95% CI)p Value†
Scenario 4 (worst case exposure to airborne Legionella)<10322‡775941
⩾10310§225741.56 (0.74 to 3.30)0.17
⩾1046103312.05 (0.83 to 5.05)0.10
Scenario 5 (frequency weighted exposure to airborne Legionella)<10322796641
⩾10310205041.77 (0.84 to 3.73)0.10
⩾104272581.00 (0.23 to 4.24)0.61
  • *Concentration in Legionella FISH/l of air

  • †Incidence density χ2 test, one-sided p.

  • ‡Subjects with PF-like clinical symptoms; these are not PF cases, in absence of contaminated water or aerosol

  • §Only the cases associated with contaminated aerosols are taken into account.