Respiratory Syncytial Virus (RSV) is a common, contagious virus that causes infections of the respiratory tract, affecting people of all ages. While it often produces symptoms resembling a mild cold in healthy adults, it can lead to serious conditions like bronchiolitis and pneumonia, particularly in infants, young children, and older adults. Because RSV symptoms overlap with other respiratory illnesses, diagnostic testing is necessary for definitive confirmation and to guide medical management and infection control.
Different Methods for Collecting RSV Samples
The term “swabbing” refers to collecting respiratory secretions to check for the presence of the virus. Obtaining an adequate sample is directly related to the accuracy of the final test result.
The most common and effective collection method is the nasal aspirate or wash, often utilized in hospital settings for infants who carry a higher viral load. This technique involves introducing sterile saline solution into the nose and then gently suctioning the fluid back out for analysis.
The nasopharyngeal (NP) swab is a widely used alternative, especially in outpatient settings, due to its simplicity and suitability for molecular tests. A simple nasal swab that collects a sample just inside the nostril is generally less sensitive because it may not reach the site where the virus is most concentrated.
The goal of any collection method is to gather cells and secretions from the nasopharynx, the area where the back of the nose meets the throat. This deep collection site is where the virus actively replicates, offering the highest likelihood of capturing the viral material needed for an accurate test.
Detailed Steps for Nasopharyngeal Swabbing
Before collection, the healthcare professional ensures a sterile environment, washes their hands thoroughly, and puts on the necessary personal protective equipment. The patient is asked to tilt their head slightly backward, which helps align the nasal passage for the deepest possible access. Clearing the nasal passages of excess mucus by gently blowing the nose beforehand can improve the quality of the specimen.
The specialized NP swab, which has a flexible shaft and a fine, flocked tip, is removed from its sterile packaging. The collector estimates the proper insertion depth by measuring the distance from the patient’s nostril to the front of their ear, as the distance to the nasopharynx is approximately half of this measurement. This visualization helps prevent the swab from being inserted too shallowly or too far.
The swab is gently inserted into one nostril, following the natural curve along the floor of the nasal passage, not angling upward toward the eye. Insertion continues until the pre-visualized depth is reached or until slight resistance is met at the posterior nasopharynx. This point is the target area where the viral load is highest.
Once fully inserted, the swab is rotated against the nasopharyngeal wall for several seconds, typically between five and ten seconds. This rotation ensures sufficient respiratory cells and secretions are absorbed onto the flocked tip. The accuracy of the test hinges on collecting infected cells, not just surface mucus. The patient may feel a temporary, tickling sensation.
The swab is slowly withdrawn from the nostril, avoiding contact with other surfaces to prevent contamination. The swab tip is immediately placed into the designated transport tube, which contains a viral transport medium (VTM) or saline solution to preserve the sample. The swab’s shaft is then broken off at a pre-marked break-point, allowing the tip to remain submerged in the transport medium.
Interpreting RSV Test Results
Once the respiratory sample is collected and transported to the laboratory, it is analyzed using one of two primary testing methods. The choice of test method impacts the time to result and the overall sensitivity of the diagnosis.
Rapid Antigen Tests
Rapid Antigen Tests are commonly used because they provide quick results, often in under an hour, by detecting viral proteins (antigens) in the sample. However, these tests are less sensitive and may produce a false negative result, especially in older children and adults who tend to have a lower viral concentration.
Nucleic Acid Amplification Tests (NAAT)
A more sensitive option is the Nucleic Acid Amplification Test (NAAT), such as the reverse transcriptase-polymerase chain reaction (RT-PCR). PCR tests look for the specific genetic material (RNA) of the virus and are capable of detecting much smaller amounts of the pathogen.
A positive test result confirms the presence of an RSV infection and helps guide clinical decisions regarding isolation and supportive care. A negative result, particularly from a rapid antigen test, does not eliminate the possibility of infection if the patient has strong symptoms. In such cases, a more sensitive PCR test may be used to confirm the finding. Test results are interpreted alongside the patient’s age, symptoms, and prevalence of RSV in the community.