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Sampling for Chlamydia trachomatis:
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Introduction:
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How to collect the specimens?
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How can you keep the Chlamydiae in a viable form after the specimen is
collected?
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Specimen collection
and transport are very important for the accuracy of C.trachomatis diagnostic
testing. For all diagnostic C.trachomatis tests, culture or nonculture,
the sensitive and specificity are directly related to the adequacy of the
specimen collected. Because Chlamydiae are obligate intracellular pathogens,
the objective of specimen collection should usually be to include the host
cells that harbor the organism. Specimens that contain secretions or exudate
but lack the cells that harbor Chlamydiae (columnar cells) are not satisfactory.
The place where
specimen is going to be taken depends on disease syndrome. For example;
conjunctivitis / conjunctiva, urethritis / urethra, cervicitis / cervix.
Urine is not
a suitable sample for cell culture.
- How to collect the specimens?
The specimens can be collected from:
The most common anatomic site used to obtain specimens for the isolation of C.trachomatis from women is the endocervix, which is sample with a swab (dacron, cotton, rayon swabs may be used. Other may be toxic for cell culture or Chlamydiae) or cytologic brush (may induce bleeding which may inhibit some nonculture tests).
* Firstly, remove and discharge exocervical mucus and pus with a cotton or dacron swab.
1)
2)3)
The preferred site of sample collection from males is the anterior urethra. Patients should not urinate 1 hour before sampling, because urination will reduce sensitivity of most diagnostic tests by washing out infected columnar cells. Use a small swab with narrow shaft.
* Firstly, express and discharge any pus or exudate.
* Insert the swab 3 to 4 cm into the urethra.
1)
2)
* Gently remove any purulent exudate if present.
* Rotate swab tip over conjunctival surface.
* Place the swab
in a transport tube immediately.
- How can you keep the Chlamydiae in a viable form after the specimen is collected?
Media for the
transport of specimens for chlamydial culture have consisted of variations
of medium formulations originally developed for the transport of Rickettsiae,
most commonly 2-sucrose phosphate, or sucrose-glutamate phosphate.
The addition of 2 to 5% fetal bovine serum helps to preserve the
viability of Chlamydiae in specimens that must be frozen. Antimicrobial
agents to which Chlamydiae are not susceptible are often added to the
transport medium to inhibit or prevent the growth of fungi and bacteria
present in clinical specimens. Recently, synthetic transport media
for culture and some nonculture tests have been developed and approved.
The isolation
is optimized if specimens are refrigerated immediately after collection
at 2 to 8 °C and kept at this temperature during transport
to the laboratory. The time between collection and laboratory processing
of specimens for culture should ideally be less than 48 hour, however,
specimens for culture that cannot be processed within this time may be
frozen at -70°C until processed (20% loss of viability). Freezing
specimens or cultures at -20°C has a deleterious effect on the
viability and antigens of C.trachomatis and should be avoided.