9
Presentation
Legionellosis-especially Legionnaires’ disease—is a leading cause of
disease, disability and death in developed countries.
Legionella
, a pathogenic
bacterium, was identified in 1977 as the causative agent of legionellosis.
Premiseplumbing, includingbothpotableandnon-potable (utility)building
water systems, is now recognized as the primary source of legionellosis.
Building water systems have characteristics that make themparticularly
susceptible to microbial colonization. Complex networks of relatively small
diameter pipes provide high surface-to-volume ratios, where water can
stagnate for long periods. Water heaters and other necessary processing
equipment further complicate building water systems and can change water
in ways that affect
Legionella
.
Legionella
contamination of building water systems is primarily
a function of natural biofilms, the complex heterogeneous microbial
ecosystems that develop on virtually all surfaces in contact with non-sterile
water.
Legionella
from colonized plumbing can enter the environment
when pieces of biofilm exit the system through a tap and are broadcast in
bio-aerosols.
Legionella
-parasitized protozoa may be similarly released and
disseminated. When the airborne, virulent particles enter deep into the gas-
exchange regions of the respiratory system of a susceptible host, they infect
and replicate within alveolar macrophages, causing Legionnaires’ disease.
Nearly 40 years of research on
Legionella
and legionellosis has expanded
our understanding, and there are a number of aspects for which there is
broad scientific consensus.
• Parasitized protozoa that graze on biofilm play a defining role in
Legionella
virulence, amplification and transmission.
