Biomedical Engineering Reference
In-Depth Information
disease have been linked to contaminated sources of aerosolized water, and
from water-holding systems. The names of the disease and the organism
derive from the first diagnosed epidemic, occurring in members of an
American Legion who attended a bicentennial convention in Philadelphia, in
July, 1976. Direct person-to-person spread has not been established. Disease
most often occurs in immune-compromised individuals and the elderly.
Infection is usually pulmonary and can be fatal. Pontiac fever is a milder
form of Legionnaire's disease. Between 10 000 and 50 000 cases of
Legionnaire's disease occur each year in the United States. The bacteria can
be visualized in tissue sections with a silver stain. Aside from Legionella
pneumophila, there are more than 50 species of Legionella, some of which
have been shown to produce Legionnaire's disease.
DNA analysis of species of Legionella demonstrated sequence dissimila-
rities, suggesting that Genus Legionella could be assigned several genera
[39]. Genus Fluoribacter was created as a new genus in Class Legionella-
ceae, and this Genus was assigned Fluoribacter bozemanae, formerly Legio-
nella bozemanae. The species in Genus Fluoribacter behave clinically like
Legionella species.
Gamma Proteobacteria
Pasteurellales
Pasteurellaceae
*Aggregatibacter
*Haemophilus
*Pasteurella
Class Pasteurellaceae contains numerous species of factultative anaerobic bacte-
ria, that are, in most cases, rod-shaped. Most species live as commensals in ver-
tebrates, and are found primarily in the upper respiratory tracts, reproductive
tracts and, in some cases, the gastrointestinal tract. Three genera contain species
pathogenic in humans: Aggregatibacter, Haemophilus, and Pasteurella.
Genus Aggregatibacter contains the oral commensal Aggregatibacter
actinomycetemcomitans, formerly Actinobacillus actinomycetemcomitans,
which causes an aggressive form of periodontitis.
Genus Haemophilus contains the pathogenic species: Haemophilus influ-
enzae, Haemophilus parainfluenzae, and Haemophilus ducreyi.
Haemophilus influenzae is found in the upper respiratory tract of normal
individuals. It causes pneumonitis, meningitis, conjunctivitis, otitis media, and
bacteremia, in infants and young children. An unencapsulated strain causes con-
junctivitis and otitis media. Its species name, influenzae, was assigned when the
bacteria was mistakenly thought to be the cause of influenza. Influenza, also
known as the flu, is caused exclusively by the influenza virus, a Group V
Orthomyxovirus (Chapter 43).
Haemophilus parainfluenzae causes some cases of endocarditis. It is
included among the HACEK organisms (see Glossary item HACEK).
