Clinic
Pneumonia is an acute or chronic inflammation of the lung parenchyma mostly caused by infections.
The World Health Organisation (WHO) estimates that pneumonia is responsible for the death of 3-4 million people each year, mainly infants and elderly people. Thus pneumonia is at the third place as a cause of infectious death worldwide. In contrast to nosocomial pneumonia, Community Acquired Pneumonia (CAP) refers to pneumonia acquired outside of hospitals or extended-care facilities. In Germany CAP is estimated to affect 800.000 persons per year, with about one third requiring hospitalisation. Thus Community Acquired Pneumonia leads more often to hospitalisation than myocardial infarction or apoplectic stroke. Pneumonia is the eighth leading cause of death in Germany - 20.000 patients with the disease died in the year 2003 (data from the Federal Statistical Office Germany). It also exacts an extensive social cost, of more than 500 million Euro per year.
Treatment of the Community Acquired Pneumonia requires experience because diagnostic of the specific pathogens is time-expensive (e.g. culture on special media) but therapy had to start as soon as possible. Thus most of the pathogens are not identified when therapy had begun.
Pathogens causing Community Acquired Pneumonia
Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis are the most frequent pathogens causing
Community Acquired Pneumonia. The so-called atypical pathogens include Mycoplasma pneumoniae and Legionella pneumophila. Staphylococci and Gram-negative enterobacteria are less important in this regard.
Typical pathogens causing CAP
Streptococcus pneumoniae
Streptococcus pneumoniae is worldwide the most common pathogen of pneumonia, bacteremia, meningitides and other potentially threateningly infections. Studies of pharyngeal flora indicate that 5 to 25% of healthy persons are carriers of pneumococci, with the highest rates noted in winter for children and parents of young children.
Infections often occur endogenous and will be promoted by disorders of the local and systemic immune-defense system.
S. pneumoniae is by far the most common pathogen of CAP, causing up to 70% of cases.
Haemophilus influenzae
Haemophilus influenzae is a Gram-negative rod with both encapsulated and non-encapsulated strains. It is a common resident of the nasopharyngeal mucosa in 2-5 % of the population without the development of disease. Transmission is by direct contact or by inhalation of respiratory aerosol. Long recognized as a respiratory pathogen in children, particularly younger than 5 years of age, it is also known to cause pneumonia in adults with weak immune system.
After S. pneumoniae, H. influenzae is the most common cause of community-acquired bacterial lung infections in adults.
Moraxella catarrhalis
Moraxella catarrhalis (synonyms: Branhamella catarrhalis, Neisseria catarrhalis) is a Gram-negative,
aerobic diplococcus that is a common inhabitant of the human upper respiratory tract.
The bacterium is now considered an important cause of upper respiratory tract infections in otherwise healthy children and
elderly people. Furthermore, M. catarrhalis causes lower respiratory tract infections, particularly in adults with chronic obstructive pulmonary disease (COPD).
Atypical pathogens causing CAP
Atypical pathogens causing pneumonia cannot be detected by conventional cultures but are responsible for up to 40% of CAPcases. Diseases caused by atypical pathogens can be poorly distinguished from infections with other bacteria and viruses (e.g. Adeno-, Influnza, Parainfluenza, RS-viruses etc). But contrary to these, they can be systematic medicated and therefore they have great diagnostic importance.
Mycoplasma pneumoniae
Mycoplasmas are the smallest free-living organisms. These organisms are unique among prokaryotes in that they lack a cell wall.
Mycoplasma pneumoniae is the most common pathogen of lung infections in persons aged 5 to 35 years. Transmission is by
person-to-person contact. The culture on special media takes several weeks. After inhalation of respiratory aerosols, the organism attaches to and destroys ciliated epithelial cells of the respiratory tract.
Legionella pneumophila
Legionella is a Gram-negative rod, which is found ubiquitous in the environment. Transmission is thought to occur via
inhalation of aerosolized mist from warm water sources (e.g., whirlpools, showers, air conditioners) contaminated with the bacterium.
Direct inhalation is the most likely method of transmission, with aerosol-generating systems playing a crucial role.
Person-to-person spread has not been reported. In the alveoles the pathogen causes an inflammation passing into a lung and pleural
inflammation. Legionella species accounts for 1 to 8% of community-acquired pneumonias that result in hospitalisation.
Of these, the most common agent is L. pneumophila (85 to 90% of cases). Even with appropriate treatment, mortality is = 15%
in community-acquired cases and is higher among immunosuppressed or hospitalised patients.
Advantages
- Detection of the most common CAP pathogens with a multiplex PCR on one strip
- an inbuilt control ensures that human cellular DNA has been extracted
and amplified from the starting test material
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