• A negative test does not rule out infection.
• Available Oct 1 - May 31
  • Do not order in the off season, as false positive results are more likely when influenza prevelance is low
  • As an alternative in the off-season, Influenza A/B PCR (8810) may be ordered

NP swab:

ESwab flexible mini-tip collection kit (blue)

 NP washing:

Screw cap plastic container (sterile)

     Nasopharyngeal (NP) swab collection

1. Tip the patient’s head back.
2. Gently insert the NP swab into the nostril parallel to the palate (not upwards) until resistance is encountered or the distance is equivalent to that from the ear to the nostril of the patient, indicating contact with the nasopharynx.   
1. If any resistance is met in the passageways, do not force the swab; back off and try reinserting it at a different angle, closer to the floor of the nasal canal, or try the other nostril.
3. Gently rub and roll the swab for 10-15 seconds while the swab is in contact with the nasopharyngeal wall.
4. The CDC recommends leaving the swab in place for several seconds to absorb secretions.
5. Slowly remove the swab and place in the transport medium.
6. Break the swab shaft so that it fits into the medium container and recap tightly.
7. Label the specimen appropriately. Document the source “NP” on the label.

New England Journal of Medicine video on NP swab collection: Nasopharyngeal Swab Collection Video

Liquid transport media (Eswab mini tip, M4RT, UTM, M4, M5, Stuarts or Aimes)

Screw cap plastic container (sterile)

1. With patient in supine position, tilt head back at 70^o angle.
2. Attach sterile syringe to catheter. Insert catheter into nostril and instill 2 to 3 mL normal bacteriostatic saline into one nostril and pharynx.
3. Aspirate fluid out of nostril with syringe.
4. Gently suction with syringe while withdrawing catheter.
5. Place washings into a screw capped container for transport.

Optimal 1-3 mL normal saline (excessive volumes decrease test sensitivity)

Screw cap plastic container (sterile)

Refrigerated - 72 hrs

• Improper label (unlabeled or mislabeled)
• Time delay between time of collection and receipt of specimen
• Improper transport container
  • Specimens collected using eSwab standard tip collection kits
• Improper transport temperature
• Inappropriate specimen type
  • Nasal swabs 
• Leaking container

Immunoassay

When to order the Influenza Antigen:

• Test in only available during influenza season, October 1^st – May 31^st, due to the increased false positive results of the antigen test when disease prevalence is low.

• Non-seriously ill outpatient

• Influenza prevalence is high

Reliability and interpretation of the Influenza Antigen:

• As compared to RT-PCR, the influenza antigen test has a positive percent agreement of 81-86% and a negative percent agreement of 97-99%.

• When influenza prevalence in the community is low, false positive (and true negative) results are more likely to occur

• When influenza prevalence is high, false negative (and true positive) results are more likely to occur