CHLAMYDIA PNEUMONIAE
Introduction
Chlamydia pneumoniae, (also more recently known as Chlamydophila pneumoniae), is an emerging infective agent that causes both upper and lower respiratory tract infections.
Chlamydophila pneumoniae infection is often mild.
Asymptomatic carriers may be an important source of infection.
Outbreaks of C. pneumoniae have been reported in closed populations.
Primary infection appears to produce for significant symptoms compared with reinfection.
History
Chlamydia pneumoniae is more recently known as Chlamydophila pneumoniae
Epidemiology
C. pneumoniae is emerging as a frequent cause of both upper and lower respiratory tract infections.
It appears to be a common cause of mild pneumonia, especially in school age children.
Up to 10 % of cases of community acquired pneumonia can be attributed to this organism.
Asymptomatic carriage occurs in 2 - 5 per cent of the population.
Only about 10 per cent of infections result in pneumonia.
Epidemics of respiratory illness can occur and these usually occur in institutional settings such as military barracks or nursing homes.
Pathology
Organism
●Chlamydophila pneumoniae, is an obligate intracellular bacterium.
Micrograph showing cells infected with the elementary bodies and reticular bodies of the Chlamydia pneumoniae organism. (Journal of Antimicrobial Chemotherapy (2003) 52, 497 499 DOI: 10.1093/jac/dkg371)
See also Appendix 1 below
Reservoir
●Humans
Transmission
●Transmission occurs person-to-person via respiratory secretions.
Incubation Period
●The incubation period is approximately 21 days.
Period of communicability
●Asymptomatic carriers may be an important source of infection.
●Symptomatic patients can carry the bacteria in the nasopharynx for months after illness.
Susceptibility & resistance
Everyone is susceptible to infection, with the risk of clinical disease increasing in patients with a chronic medical condition.
Immunosuppressed patients do not seem to be more susceptible, however older debilitated patients may develop severe disease.
Initial infection occurs in school age children with up to 50 per cent of the population becoming seropositive by 20 years of age.
Infection does not produce complete immunity and re-infection can occur.
Clinical Features
Infection may be:
1.Asymptomatic:
●The initial infection appears to be the most severe with reinfection often being asymptomatic.
2.Mild infection:
●URTI, with pharyngitis or sinusitis.
●Bronchitis, cough may occasionally persist for several weeks despite appropriate antibiotic therapy.
3.Pneumonia
●More serious illness in the form of a pneumonia may also be seen.
4.It may be an infectious precipitant of asthma
Investigations
1.Serology:
●Serological diagnosis is made by detecting a four-fold rise in antibody titre using microimmunofluorescence (MIF).
MIF is the only serological test that can reliably differentiate different chlamydial species.
●A single antibody titer is of little diagnostic value on its own as the seroprevalence of antibodies to C. pneumoniae approaches 50 % in the adult population.
●Seroconversion may take up to eight weeks in an initial infection but it tends to occur much more quickly in reinfection (one to two weeks).
●False positive antibody tests can occur in the presence of a positive rheumatoid factor.
2.Culture:
●Culture of nasopharyngeal aspirates, throat swabs or bronchial lavage fluid is possible.
●Swabs should be placed in chlamydia transport medium whilst other specimens can be collected in the usual containers. Discuss with the laboratory about the best method of collection of samples.
3.PCR:
●Diagnosis by PCR is available through the Victorian Infectious Diseases Reference Laboratory (VIDRL).
●This is not currently routinely done however, rather it is only being used in investigation of outbreaks of respiratory illness where conventional testing has not revealed the cause of infection.
4.CXR:
●Non specific bilateral infiltrates may be seen
Management
Antibiotics:
Options include:2
●Doxycycline
●Azithromycin
●Clarithromycin
Duration of therapy is generally 7- 10 days for doxycycline and clarithromycin
Duration of therapy for azithromycin can be 3- 5 days because it has a long intracellular half life.
Isolation:
●Isolation is not necessary, but the patient should be counseled on good respiratory hygiene, such as coughing into disposable tissues.
Notification:
Notification is not required.
School exclusion:
School exclusion is not required.
Appendix 1
Life cycle of Chlamydia pneumoniae:
(Wikipedia)
Chlamydia pneumoniae is a gram-negative obligate intracellular organism that exists in two forms.
The elementary body is the infectious, metabolically inactive extracellular form, and the reticulate body is the noninfectious, metabolically active intracellular form.
The elemental body gets endocytosed and then changes into the reticulate body, which subsequently forms the characteristic intracytoplasmic inclusions.
Approximately 36 hours later, the reticulate body condenses back into the elemental body, which undergoes release by cytolysis or exocytosis at 48 hours.
References
1.Chlamydia Pneumoniae in The Blue Book Website, Accessed July 2016.
2.eTG - March 2016
●Antibiotic Therapeutic Guidelines November 2014.