Chlamydophila pneumoniae

‍Chlamydia pneumoniae is a common intracellular bacterial pathogen causing a range of respiratory infections such as pneumonia, bronchitis, sinusitis, and pharyngitis. 

It is widely prevalent globally, transmitted through respiratory routes, and has a high reinfection rate throughout life. 

While often asymptomatic or mildly symptomatic, C. pneumoniae can lead to severe respiratory illnesses in about 30% of cases. 

Beyond respiratory infections, it has been implicated in chronic conditions like asthma, chronic obstructive pulmonary disease (COPD), and even cardiovascular diseases such as atherosclerosis and coronary heart disease. 

The bacterium's persistence in the body, despite antibiotic treatment, poses significant challenges, necessitating further research into its pathogenesis and effective treatment strategies. 

This article explores the impact, diagnosis, and treatment options for C. pneumoniae.

Chlamydophila pneumoniae: An Overview

Chlamydophila pneumoniae is a common intracellular bacterial respiratory pathogen with a unique biphasic life cycle [5.].

It is widely distributed globally and transmitted from human to human via the respiratory route, infecting the majority of the world's population; it has a high prevalence of reinfection throughout life [1., 5.].

C. pneumoniae causes about 10% of community-acquired pneumonia and 5% of pharyngitis, bronchitis, and sinusitis [2.].

In Western countries, new infections are most common between ages 5 and 15, and seroprevalence is higher in adult males [1.].

Most infections (70%) are asymptomatic or mildly symptomatic, but about 30% can cause severe respiratory illnesses [5.].

‍C. pneumoniae can cause various respiratory illnesses, including pneumonia, bronchitis, sinusitis, and pharyngitis [5.].

After an acute infection, C. pneumoniae can persist in a form that is resistant to antibiotics and potentially contributes to chronic respiratory conditions such as asthma, chronic bronchitis, and COPD [5.].

Additionally, evidence suggests a potential link between C. pneumoniae infection and atherosclerosis as the bacterium has been found in atherosclerotic plaques. It is also associated with coronary heart disease and acute myocardial infarction [1.]. 

It has also been implicated in other conditions like erythema nodosum and sarcoidosis [2.].

Naming and Classification of C. pneumoniae [7., 8.] 

Chlamydia pneumoniae is part of the Chlamydiae order, which contains obligate intracellular pathogens. 

The order initially comprised one genus, Chlamydia, with four recognized species: C. trachomatis, C. psittaci, C. pneumoniae, and C. pecorum. 

C. trachomatis and C. pneumoniae are primary human pathogens, while C. psittaci causes zoonosis.

Recent taxonomic analysis has led to a proposed reclassification, suggesting the division of the genus Chlamydia into two genera: Chlamydia and Chlamydophila. 

Under this new classification, C. trachomatis would be joined by two new species, Chlamydia muridarum and Chlamydia suis. 

The genus Chlamydophila would include C. pecorum, C. pneumoniae, and C. psittaci, along with three new species derived from C. psittaci: Chlamydophila abortus, Chlamydophila caviae, and Chlamydophila felis. Despite ongoing controversy regarding this reclassification, the term Chlamydia is still commonly used.

‍Chlamydia pneumoniae, also known as TWAR, is distinguished from C. trachomatis and C. psittaci by its unique elementary body morphology and less than 10% DNA homology. 

Symptoms of Chlamydophila pneumoniae [1., 2., 6., 7.]

The symptoms of C. pneumoniae infections are similar to those caused by other respiratory pathogens but often present a subacute onset with pharyngitis that may resolve before bronchitis or pneumonia develops. A prolonged cough and slow recovery, even with antibiotic therapy, are common.

Diseases and Health Implications of C. pneumoniae

C. pneumoniae is associated with the following conditions: 

Respiratory Infections [2., 5.] 

• Pneumonia

• Bronchitis

• Sinusitis 

Cardiovascular Diseases

• Atherosclerosis [1.]

• Coronary artery disease [1.] 

• Myocardial infarction [1., 2.] 

Neurological Disorders

• Multiple sclerosis [4.] 

• Alzheimer's disease [4.] 

Chronic Respiratory Conditions

• Exacerbation of asthma [5.] 

• Chronic obstructive pulmonary disease (COPD) [5.]

Other Potential Associations

• Arthritis [10.] 

• Lung cancer [10.] 

• Sarcoidosis [2.] 

• Erythema Nodosum [2.] 

General Notes

• Chlamydia pneumoniae can lead to severe infections, particularly in older individuals.

• Further research is required to understand its pathogenesis and treatment strategies.

Laboratory Testing for Chlamydophila Pneumoniae

Test Information, Sample Collection and Preparation

C. pneumoniae is often tested by assessing the presence of antibodies against this organism.  Often, IgG, IgM, and IgA antibody levels are tested.

This test requires a blood draw via venipuncture. Special preparation is typically not required.

A culture may be performed, although this is not generally considered optimal as it is time-consuming [3.].

Molecular diagnostic testing is also available, which is done via real-time polymerase chain reaction (PCR). This is the recommended method per the CDC [3.].

However, other sources report that antibody assessment via serology is the preferred method [9.].

Interpretation of C. pneumoniae Test Results

Positive PCR or culture results will confirm the presence of the C pneumoniae organism. PCR has the added advantage of defining antimicrobial susceptibility [3.].

Serology tests can describe the timeline of infection, with the presence of IgM antibodies indicating a current or recent infection, and IgG antibodies indicating a past infection. IgA antibodies typically confirm an immune response in mucosal tissue, often from the respiratory or digestive tract.

C. pneumoniae IgG antibodies can persist for months to years. Seroprevalence studies show 50-70% of adults have IgG antibodies, indicating frequent reinfections [9.].

However, IgM antibodies are rarely produced in reinfections, which may limit IgM testing utility [9.].

Treatment of C. pneumoniae [6.]

Antimicrobial treatment of C. pneumoniae often consists of:

• Erythromycin

• Azithromycin (Zithromax®)

• Clarithromycin (Biaxin®)

• Levofloxacin (Levaquin®)

• Moxifloxacin (Avelox®)

Each of these has shown 70-90% success in eradicating C. pneumoniae from the respiratory tract in cases of pneumonia.

Macrolides, ketolides, tetracyclines, quinolones, and rifamycins have all shown effectiveness in vitro [6.].

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