PROCESSING OF RESPIRATORY TRACT SPECIMEN
Respiratory tract specimens can be categorized into upper and lower respiratory tract specimen. Infections of the lower respiratory tract are the leading cause mortality worldwide.
Specimen collection
| Throat swab | Sputum | Induced sputum | Tracheal aspirate | Broncho-alveolar lavage |
| o Diphtheria, Vincent’s angina, thrush and gonococcal pharyngeal infection could also be diagnosed on special request.
o Patient’s face is turned against the light and the patient is asked to open the mouth wide and say ah, tongue is gently depressed using tongue depressor
o Swab is rubbed firmly over the back of the throat, both tonsils and any area of inflammation, exudation or ulceration. .
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The patient should be instructed as follows:
o Not to gargle prior collection o Not expectorate saliva or postnasal discharge o To Collect expectorated sputum specimens into a sterile container
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Induced sputa should only be tested for the presence of Mycobacterium tuberculosis , other Mycobacterium spp and
PJP (in case of HIV positive patients only). o Buccal mucosa,tongue and gums are brushed with sterile water and brushed for 5 to 10 min prior to the procedure.
o 20 to 30 ml of 3% NaCl is inhaled by patient using nebulizer
o Induced sputum specimens are collected into a tightly capped sterile container
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The specimen is collected into a sterile sputum trap and then aseptically transfered in a sterile container.
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Collected by trained personnel. |
Transport:
- Samples should be received and handled by the laboratory as soon as possible after collection.
- Specimens can be stored at 2 to 8oC until samples can be transported or processed by the laboratory.
Processing and reporting
| Throat swab | Sputum / ET aspirate | Broncho-Alveolar Lavage |
| o Swab is rolled over agar surface, and streaked in four quadrants on blood agar supplemented with colistin and nalidixic acid (incubated at 37oC with 5-7% CO2)
o Plates are observed for beta hemolytic Streptococci. o Reincubate further till 48 hours in case of no significant growth. o If there are beta hemolytic then catalase test is performed, proceeding with lancefield grouping if its negative
Interpretation and reporting
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Most purulent or blood-tinged portion of the specimen is selected to examine microscopically
On the basis of gram stain, the sputum sample is processed as follows: o If pus cells are present and epithelial cells are absent, the media is inoculated. o If pus cells are present with moderate to numerous epithelial cells or no pus cells with numerous epithelial cells, the sample is rejected and the physician is asked for another sample
Microscopic criteria for specimen adequacy in case of tracheal aspirates is yet to be established.
Specimen is inoculated on:
o Chocolate agar (incubated at 37oC with 5-7% CO2) o Sheep blood agar or blood agar supplemented with colistin and nalidixic acid (incubated at 37oC with 5-7% CO2) o Mackonkey agar (incubated at 37oC, ambient air)
Interpretation and reporting:
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If AFB investigation is required, separate a portion for mycobacterial culture of AFB Smear prior to processing
Using calibrated loop method, specimen is inoculated by 0.001µl loop on: o Chocolate agar (incubated at 37oC with 5-7% CO2) o Sheep blood agar (incubated at 37oC with 5-7% CO2) o Mackonkey agar (incubated at 37oC, ambient air)
Interpretation and reporting:
Any count of ≥ 104 is considered as significant. Therefore growth of 10 or more than 10 colonies is identified and reported |
Table 1: Guidelines for reporting of primary pathogens for lower respiratory tract specimen.
| Action | Organisms |
| Examine for and always report.
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| Always report, but do not make an effort to find low numbers, unless they are seen in the smear.
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| Report the following in case of ICU admission or immunocompromised |
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Reference:
1– Henry D Isenberg. Clinical Microbiology Procedure Handbook, 3rd ed. Vol. 1 ASM press.
Updated July 2018
Dr. Yusra Shafquat
Year 5 Resident
Department of Pathology and Laboratory Medicine
Aga Khan University Hospital karachi