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Updated: Apr 16, 2026
Legionella pneumophila Outer Membrane Vesicles: Isolation and Analysis of Their Pro-inflammatory Potential on Macrophages
Published on: February 22, 2017
[Legionella spp. contamination in indoor air: preliminary results of an Italian multicenter study]
Maria Teresa Montagna1, Osvalda De Giglio, Christian Napoli
1Dipartimento di scienze biomediche e oncologia umana, Sezione di igiene, Università degli studi di Bari "Aldo Moro". igiene.dimo@uniba.it.
Objective:
To propose a standardized protocol for the evaluation of Legionella contamination in air.
Design:
A bathroom having a Legionella contamination in water >1,000 cfu/l was selected in 10 different healthcare facilities. Air contamination was assessed by active (Surface Air System, SAS) and passive (Index of Microbial Air, IMA) sampling for 8 hours, about 1 m away from the floor and 50 cm from the tap water. Two hundred liters of air were sampled by SAS every 12 min, after flushing water for 2 min. The IMA value was calculated as the mean value of colony forming units/16 plates exposed during sampling (2 plates/hour). Water contamination was evaluated at T0, after 4 and 8 hours, according to the standard methods.
Results:
Air contamination by Legionella was found in three healthcare facilities (one with active and two with passive sampling), showing a concomitant tap water contamination (median=40,000; range 1,100-43,000 cfu/l). The remaining seven hospitals isolated Legionella spp. exclusively from water samples (median=8,000; range 1,200-70,000 cfu/l).
Conclusions:
Our data suggest that environmental Legionella contamination cannot be assessed only through the air sampling, even in the presence of an important water contamination.
Insights
Evaluating airborne Legionella requires more than just air sampling, even with significant water contamination. This study highlights limitations in current air assessment methods for Legionella environmental monitoring.
Area of Science:
- Environmental microbiology
- Infectious disease control
- Public health
Context:
- Legionella contamination poses a significant risk in healthcare settings.
- Accurate environmental monitoring is crucial for preventing Legionnaires' disease.
- Existing air sampling methods may not fully capture Legionella presence.
Purpose:
- To evaluate the effectiveness of air sampling protocols for detecting Legionella.
- To compare active (Surface Air System) and passive (Index of Microbial Air) air sampling methods.
- To assess the correlation between water and air contamination levels in healthcare facilities.
Summary:
- Legionella contamination was assessed in water and air across 10 healthcare facilities.
- Air sampling detected Legionella in three facilities with concurrent water contamination.
- Seven facilities showed Legionella exclusively in water samples, indicating limitations of air monitoring.
Impact:
- Suggests that air sampling alone is insufficient for assessing environmental Legionella risk.
- Highlights the need for comprehensive water and air monitoring strategies.
- Informs the development of standardized protocols for Legionella environmental surveillance.
