Nasopharyngeal (NP) swab is the optimal upper respiratory tract specimen collection method for viral respiratory infections such as respiratory syncytial virus (RSV), SARS-CoV-2, influenza virus A & B, and parainfluenza virus. Nasopharyngeal swabs are also collected for the diagnosis of bacterial infections such as Bordetella pertusis (whooping cough), Mycoplasma pneumoniae and to screen carriers of meningococci.
- Sterile Dacron/nylon swab with flexible plastic shaft. (Cotton-tipped or calcium alginate swabs are not acceptable)
- Universal Transport medium or Viral transport media (should contain 1-3 mL of sterile viral transport medium).
- Personal protection equipment, PPEs (i.e., mask, gloves, eye protection, gowns).
- Requisition form
- Biohazard label
- Biohazard bag
- Shipping container with cold packs
Note: Calcium alginate swab and swab with wooden shaft must not be used. These materials can inactivate viral particles and/or inhibit the PCR test. Furthermore, wooden shafts are likely to cause patient injury.
Before Sample Collection
- Explain procedure to the patient. Be sure to advise patients about potential discomfort during sample collection
- Wash hands.
- Put on appropriate personal protective equipment (at a minimum, gloves, and facemask) to protect yourself in case the patient coughs or sneezes during sample collection. The level of PPEs depends on the infectiousness of the suspected pathogen. For example, in suspected coronavirus (SARS-CoV-2) infections, the examiner should wear a N-95 respirator mask, gown, protective goggles, and gloves.
- If the patient/resident has a lot of mucous in his/her nose, this can interfere with the collection of cells. Ask the patient to blow air into a tissue to clear excess secretions from the nasal passages.
- Seat the patient in a comfortable bed. It is best if the patient is placed in a high fowler’s position in bed with the back of the head supported. It may be necessary to have a second person available to assist with the collection
Nasopharyngeal swab collection procedure
- Tilt the patient head back 70 degrees and supported with your nondominant hand. If necessary lean the patient head against the wall to minimize jerky movements. Instruct the patient to close eyes to lessen the mild discomfort of the procedure.
- Stand slightly offset from the patient to avoid respiratory contamination in case of sudden cough or sneeze.
- Hold the swab like a pen between the thumb, index and middle fingers.
- Start by inserting the swab horizontally into the left or right nostril. Carefully advance the swab while maintaining a course that is close to both the septum and floor of the nose, parallel to the palate, until the resistance (resistance is felt when the swab reaches the posterior nasopharynx) is felt. Ideally, you should collect two nasopharyngeal swabs.
Note: The swab should reach depth equal to the distance from nostrils to the outer opening of the ear. When collecting samples from adult patients this corresponds to a travel distance of approximately about 5-6 cm or 2 inches.
- Leave swab in place for several seconds to absorb secretions while gently wiping the wall by twisting the swab shaft for 10-15 seconds.
- Slowly and gently remove the swab.
- Immediately insert the swab into sterile viral transport media tube and snap/cut off the applicator stick, replace the cap and seal the tube tightly.
Nasopharyngeal swab collection for laboratory diagnosis of COVID-19
SARS-CoV-2 is a highly infectious virus so the above-mentioned nasopharyngeal swab collection procedure is modified giving special care to the use of PPEs and extra steps to prevent the spread of the pathogen.
Sample packaging and transport
- Label the specimen on viral transport media using a bar code or permanent marker.
- Place the specimen in a laboratory transport biohazard bag.
- Fill out the requisition form.
- Place the sample on refrigerator ice packs or at 4°C for transport and promptly transport the laboratory. If delivery will be delayed for more than 4 days, the specimen should be frozen at -70°C.
If there is a requirement of transportation or shipping of samples, samples should be packed in a basic triple packaging system with a primary watertight container wrapped with absorbent material, secondary watertight container, and an outer shipping package.
References and further readings
- CDC, “Interim Guidelines for Collecting, Handling, and Testing Clinical Specimens from Persons for Coronavirus Disease 2019 (COVID-19),” NETEC Repository.
- World Health Organization. (2011). Manual for the laboratory diagnosis and virological surveillance of influenza. World Health Organization.
- Koneman’s Color Atlas and Textbook of Diagnostic Microbiology