A nasopharyngeal culture is used to identify pathogenic (disease-causing) organisms present in the nasal cavity that may cause upper respiratory tract symptoms.
Some organisms that cause upper respiratory infections are carried primarily in the nasopharynx, or back of the nose. The person carrying these pathogenic bacteria may have no symptoms, but can still infect others with the pathogen and resulting illness. The most serious of these organisms is Neisseriea meningitidis, which causes meningitis or blood stream infection in infants. By culturing a sample from the nasopharynx, the physician can identify this organism, and others, in the asymptomatic carrier. The procedure can also be used as a substitute for a throat culture in infants, the elderly patient, the debilitated patient, or in cases where a throat culture is difficult to obtain.
The technician taking the specimen should wear gloves to prevent spreading infectious organisms. The patient should not be taking antibiotics, as these drugs may influence the test results.
The patient should cough before collection of the specimen. Then, as the patient tilts his or her head backwards, the caregiver will inspect the back of the throat using a penlight and tongue depressor. A swab on a flexible wire is inserted into the nostril, back to the nasal cavity and upper part of the throat. The swab is rotated quickly and then removed. Next, the swab is placed into a sterile tube with culture fluid in it for transport to the microbiology laboratory. To prevent contamination, the swab should not touch the patient's tongue or side of the nostrils.
When the sample reaches the laboratory, the swab will be spread onto an agar plate and the agar plate incubated for 24-48 hours, to allow organisms present to grow. These organisms will be identified and any pathogenic organisms may also be tested for susceptibility to specific antibiotics. This allows the treating physician to determine which antibiotics will be effective.
In most cases of upper respiratory tract infections, a throat culture is more appropriate than a nasopharyngeal culture. However, the nasopharyngeal culture should be used in cases where throat cultures are difficult to obtain or to detect the carrier states of Harmophilus influenzae and meningococcal disease.
Some researchers regard the immunoblot method as preferable to a standard culture to detect certain species of pneumococci and other organisms that cause pneumonia. The immunoblot method uses a membrane that changes color in response to a specific antigen-antibody reaction.
As of the early 2000s, polymerase chain reaction (PCR) analysis is considered more sensitive than standard culture in detecting Bordetella pertussis, the bacterium that causes whooping cough. PCR has the additional advantage of providing test results more rapidly than culture.
The procedure of inserting the swab should be described to the patient, as there is a slight discomfort associated with taking the sample. Other than that, no special preparation is necessary.
There is little to no risk involved in a nasopharyngeal culture.
Bacteria that normally grow in the nose cavity will be identified by a nasopharyngeal culture. These include nonhemolytic streptococci, alpha-hemolytic streptococci, some Neisseria species, and some types of staphylococci.
Pathogenic organisms that might be identified by this culture include
- Group A beta-hemolytic streptococci
- Bordetella pertussis, the causative agent of whooping cough
- Corynebacterium diptheriae, the causative agent of diptheria
- Staphylococcus aureus, the causative agent of many staphylococcal infections.
Additional bacteria are abnormal if they are found in large amounts. These include
- Haemophilus influenzae, a causative agent for certain types of meningitis and chronic pulmonary disease.
- Streptococcus pneumoniae, a causative agent of pneumonia
- Candida albicans, the causative agent of thrush.
Byrne, J., D. F. Saxton, P. K. Pelikan, and P. M. Nugent. Laboratory Tests, Implication for Nursing Care. 2nd ed. Menlo Park, CA: Addison-Wesley Publishing Company.
Bronsdon, M. A., K. L. O'Brien, R. R. Facklam, et al. "Immunoblot Method to Detect Streptococcus pneumoniae and Identify Multiple Serotypes from Nasopharyngeal Secretions." Journal of Clinical Microbiology 42 (April 2004): 1596-1600.
Fry, N. K., O. Tzivra, Y. T. Li, et al. "Laboratory Diagnosis of Pertussis Infections: The Role of PCR and Serology." Journal of Medical Microbiology 53 (June 2004): 519-525.
American Medical Association. 515 N. State St., Chicago, IL 60612. (312) 464-5000. http://www.ama-assn.org.
Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. http://www.cdc.gov.
Antibiotic — A drug given to stop the growth of bacteria. Antibiotics are ineffective against viruses.
Nasopharynx — The back wall of the nasal cavity where it meets the throat.
na·so·pha·ryn·ge·al cul·ture(nā'zō-fă-rin'jē-ăl kŭl'chŭr)
Microbial culture of a specimen obtained with a swab inserted through the nose into the nasopharynx.