- Nasal swab specimens are collected from both nostrils
- A sterile cotton or Dacron swab is inserted 2-3 cm into the nostril and rotated 2–3 times against thesurface of the nasal cavity
- The swab is taken out and put into a vial containing 2.5 ml of viral transport medium (5% tryptose phosphate broth, 0.5% bovine serum albumin, and antibiotics in phosphate-buffered saline provided by the lab)
Additional information
- Samples should be collected within the first 3-4 days of onset of illness
- Send to lab immediately
- Refrigerate the sample if delay is expected
Information about influenza:
- Influenza is a viral illness that typically comes in epidemics during the winter
- The symptoms include:
- Fever which is usually more severe at the beginning of the illness
- Myalgias and arthralgias
- Cough
- Rhinorrhea
- Sore throat
- Headache
- Fatigue/Malaise
- Anorexia
- Nausea/Vomiting
- Influenza is an infectious disease caused by an RNA virus of the orthomyxoviridae family, which are of three types (A, B, and C)
- Types A and B cause epidemic disease, while type C causes sporadic disease. Type A is the most common pathogenic form
- Influenza type A affects humans, birds, pigs, and horses
- Influenza types B & C only occurs in humans
Information about the test:
- Influenza nasal swab test is performed to detect the presence of influenza viral antigens or antibodies in the nasal swab specimen/ nasal cavity
- Various diagnostic tests are available to detect influenza. The sensitivity and specificity of these tests may vary depending on the laboratory that performs the test, the type of test used, and the type of specimen tested. The diagnostic tests include:
- Immunofluorescence assays
- Polymerase chain reaction (PCR)
- Rapid antigen testing
- Serology
- Viral culture
- Laboratory diagnostic methods for the detection of influenza include:
- Direct immunofluorescence tests: This test can be done on fresh samples or cells harvested from the culture by fluorescent antibody staining and observed under fluorescence microscope. These tests are labor-intensive requiring specially trained laboratory personnel and are less sensitive than culture methods
- FLU optical immunoassay (OIA) test: This test can be done on fresh samples by direct visual detection of color change. A positive result appears as a blue to purple spot on the predominant gold background
- Polymerase chain reaction (PCR): This test is a fast and sensitive way to detect the virus, differentiate between its types and subtypes, and also to quantitate the viral load of influenza virus by reverse transcriptase PCR-enzyme hybridization assay (RT-PCR-EHA)
- Rapid antigen testing: QuickVue bedside test is among the more popular methods approved by the US Food and Drug Administration, which is a fast (10-minute) test with a sensitivity of 70-80%
- Serological studies require blood sample and not nasal swab specimens
- Viral culture: This method requires 3-7 days to process and laboratory diagnosis of influenza is established once specific cytopathic effect (CPE) is observed or hemadsorption testing findings are positive. It is the most sensitive and specific test for detection
- Factors interfering with the test results include:
- Recent antimicrobial therapy
- Improper technique of collection
- Failure to place specimen in transport medium
- Viral specimen not refrigerated or maintained at cold temperature
- Failure to send specimen to lab immediately
- The clinical utility of influenza nasal swab test include the following:
- To determine whether a patient's symptoms are due to influenza infection (thus allowing for timely treatment options)
- To identify carriers of influenza type A and B viruses
- In the differential diagnosis of pathogens causing upper respiratory tract infections with similar clinical symptoms such as:
- Adenovirus
- B. pertussis
- Legionella spp.
- Mycoplasma pneumoniae
- N. meningitidis
- Parainfluenza viruses
- Respiratory syncytial virus
- Rhinovirus
- To detect a respiratory illness outbreak due to influenza, usually in closed settings such as:
- Boarding school
- Cruiseship
- Day care centre
- Hospitals
- Nursing home
- Summer camp
- Influenza is a highly contagious acute respiratory infection, which is primarily transmitted through respiratory droplets. The incubation period is usually for 1-4 days (average 2 days)
- The infectivity of influenza may vary depending on the age or the person's immunity:
- Adults are infectious a day before the onset of symptoms to approximately 5 days after illness onset
- Children are infectious for more than 10 days after the onset of symptoms
- Severely immunocompromised persons can shed virus for weeks or months
- Uncomplicated influenza illness has an abrupt onset of constitutional and respiratory signs and symptoms, resolving within 3-7 days in most people, but cough and malaise may last for more than two weeks
- Uncomplicated influenza may clinically present as:
- Arthralgia & Myalgia
- Sore throat
- Anorexia
- Coughing
- Rhinorrhea
- High fever (worse at onset of illness)
- Chills
- Fatigue
- Headache
- Irritated watering eyes
- Nausea/Vomiting
- Reddened eyes, skin (especially face), mouth, throat, and nose
- Influenza may exacerbate in certain individuals resulting in complications, hospitalization, or even death. In many cases of death, the cause will be a secondary bacterial pneumonia; however, primary influenza viral pneumonia may occur, especially in susceptible persons such as:
- Children<5 years or Adults>50 years
- Pregnancy (last trimester)
- Chronically debilitated patients, especially with those with chronic pulmonary, cardiac or renal diseases
- Nursing home patients
- Immunosuppressed patients, such as those with HIV, diabetes, hemoglobinopathies, taking chemotherapy, corticosteroids or other immunosuppressants
- Patients with cognitive dysfunction, spinal cord injuries, or other neuromuscular disorders
- In association with other conditions such as encephalopathy, transverse myelitis, myositis, myocarditis, pericarditis, and Reyes syndrome
- Healthcare providers
Additional information
- Approximately 20,000 deaths and 200,000 hospitalizations occur annually as a result of influenza virus (CDC) in US alone
- Influenza occurs as sporadic illness, epidemics, or pandemics. Epidemic disease occurs annually, especially in the winter and spring
- Emergence of global pandemics may be due to high degree of transmissibility and development of an influenza virus with a major antigenic shift in a nonimmune population. Some of the global pandemics include:
- Asiatic (Russian) flu (1889–1890) with one million deaths (Type A, subtype possibly H2N2)
- Spanish flu (1918–1920) with 40 million deaths (Type A, subtype H1N1)
- Asian flu (1957-1958) with 1 to 1.5 million deaths (Type A, subtype H2N2)
- Hong Kong flu (1968-1969) with 0.75 to 1 million deaths (Type A, subtype H3N2)
- Russian flu (1977) of Type A, subtype possibly H1N1
- Avian or bird flu (2004) in Southeast Asia of type A, subtype H5N1
- The nasal swab collection for influenza is easy, painless, and cost-effective
- This test usually utilizes the viral antigen detection method and is rapidly available and simple to perform
- For influenza viruses, the present practice in several European countries includes the collection of both nasal and throat samples that are put in the same vial for transportation to the laboratory
- Related laboratory tests include:
- Blood culture
- Chest X-ray
- Complete blood count
- Comprehensive metabolic panel
- Respiratory syncytial virus (RSV) antigen test
- Sputum microscopy and culture
- Streptococcal testing (ASO, Rapid Strep Screen)
Depending upon the test ordered, the normal result (no influenza infection detected) will be reported as:
- Negative
- Non-reactive
- No growth
A high result is a positive influenza test, which is consistent with influenza infection
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- eMedicine from WebMD®. Influenza. [Homepage on the Internet] ©1996-2006. Last updated onJanuary 8, 2007. Last accessed on January 24, 2007. Available at URL: http://www.emedicine.com/MED/topic1170.htm
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- LabTestsOnline®. Influenza Tests. [Homepage on the Internet]© 2001-2006. Last reviewed on July 20, 2006. Last accessed on January 24, 2007. Available at URL: http://www.labtestsonline.org/understanding/analytes/flu/glance.html
- Ohmit SE et al. Symptomatic predictors of influenza virus positivity in children during the influenza season. Clin Infect Dis. 2006 Sep 1;43(5):564-8. Epub 2006 Jul 12.
- Terho H et al. Nasal Swab versus Nasopharyngeal Aspirate for Isolation of Respiratory Viruses. J Clin Microbiol. 2002 November; 40(11): 4337–4339.
- UTMB Laboratory Survival Guide®. INFLUENZA A VIRUS, DIRECT. [Homepage on the Internet]© 2006. Last reviewed in February 2006. Last accessed on January 24, 2007. Available at URL: http://www.utmb.edu/lsg/LabSurvivalGuide/micro/INFLUENZAE%20A%20VIRUS%20DIRECT.html
- UTMB Laboratory Survival Guide®. INFLUENZA B VIRUS, DIRECT. [Homepage on the Internet]© 2006. Last reviewed in February 2006. Last accessed on January 24, 2007. Available at URL: http://www.utmb.edu/lsg/LabSurvivalGuide/micro/INFLUENZAE%20B%20VIRUS%20DIRECT.html