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Nasopharyngeal Culture

This test is used to evaluate nasopharyngeal secretions for the presence of pathogenic organisms. It requires direct microscopic examination of a Gramstained smear of the specimen. Preliminary identification of organisms may be used to guide clinical management and determine the need for additional testing. Cultured pathogens may then require susceptibility testing to determine appropriate antimicrobial therapy.

Purpose

• To identify pathogens causing upper respiratory tract symptoms.
• To identify proliferation of normal nasopharyngeal flora, which may be pathogenic in debilitated and other immunocompromised patients.
• To identify Bordetella pertussis and Neisseria meningitidis, especially in very young, elderly, or debilitated patients and asymptomatic carriers.
• Infrequently, to isolate viruses, especially to identify carriers of influenza virus A and B

Patient preparation

• Explain to the patient that this test is used to isolate the cause of nasopharyngeal infection.
• Describe the procedure to the patient; tell him that secretions will be obtained from the back of the nose and the throat, using a cotton tipped swab, and who will collect the specimen.
• Warn him that he may experience slight discomfort and gagging, but re­assure him that obtaining the specimen takes less than 15 seconds.

Equipment

Gloves; penlight; sterile, flexible wire swab; small, sterile, open-ended glass Pyrex tube or sterile nasal speculum; tongue blade; culture tube; transport medium (broth).

Procedure and posttest care

• Put on gloves.
• Ask the patient to cough before you begin collecting the specimen.
• Position the patient with his head tilted back.
• Using a penlight and a tongue blade, inspect the nasopharyngeal area.
• Gently pass the swab through the nostril and into the nasopharynx, keeping the swab near the septum and floor of the nose. Rotate the swab quickly and remove it.
• Alternatively, place the Pyrex tube in the patient's nostril, and carefully pass the swab through the tube into the nasopharynx. Rotate the swab for 5 seconds; then place it in the culture tube with transport medium. Remove the Pyrex tube.
• Label the specimen with the patient's name, the doctor's name, the date and time of collection, the origin of the material, and the suspected organism.
• Ideally, specimens for B. pertussis should be inoculated to fresh culture medium at the patient's bedside because of the organism's susceptibility to environmental changes.
• If the purpose of specimen collection is to isolate a virus, follow the laboratory's recommended collection technique.

Precautions

• Wear gloves when performing the procedure and handling the specimen.
• Do not let the swab touch the sides of the patient's nostril or his tongue to prevent specimen contamination

CLINICAL ALERT Laryngospasm may occur after the culture is obtained if the patient has epiglottitis or diphtheria. Keep resuscitation equipment nearby.

• Note recent anti microbial therapy or chemotherapy on the laboratory slip.
• Keep the container upright.
• Tell the laboratory if the suspected organism is Corynebacterium diphtheriae or B. pertussis because these need special growth media.
• Refrigerate a viral specimen according to your laboratory's procedure.

Normal findings

Flora commonly found in the nasopharynx include nonhemolytic streptococci, alpha-hemolytic streptococci, Neisseria species (except N. meningitidis and N. gonorrhoeae), coagulase negative staphylococci such as Staphylococcus epidermidis and, occasionally, the coagulase-positive S. aureus.

Abnormal findings

Pathogens include group A beta­hemolytic streptococci, B. pertussis, C. diphtheriae, S. aureus, N gonorrhoeae, and large amounts of Haemophilus influenzae, pneumococci, or Candida albicans.

Interfering factors

• Recent antimicrobial therapy (decrease in bacterial growth)
• Failure to use proper collection technique
• Failure to place the specimen in transport medium
• Failure to keep a viral specimen cold
• Failure to send the specimen to the laboratory immediately