Also known as:
Name: RSV, respiratory syncytial virus
Related tests:
Why is the test done?
To determine whether newborns, older people or immunocompromised patients have been infected with respiratory syncytial virus (RSV), and to identify community outbreaks, especially in certain seasons.
When is the test done?
It is usually carried out during the season when the risk of catching the virus is highest (from autumn until the end of spring) to establish whether symptoms such as a runny nose, congestion, cough and difficulty breathing are actually due to RSV infection or to other causes.
What samples are required?
Usually a nasal aspirate or wash; more rarely a nasopharyngeal swab.
What is being analysed?
This laboratory test is used to identify respiratory syncytial virus (RSV), which causes a very common respiratory infection. RSV tends to be seasonal, causing outbreaks in children, older people and immunocompromised patients that typically begin in November/December and end in early spring. In these high-risk groups, RSV can cause pneumonia and bronchitis. Affected patients may have symptoms such as persistent cough, difficulty breathing and high fever. Every year about 100,000 people are admitted to hospital with RSV infections, and there are about 11,000 deaths a year from complications of this infection, most of them in older people.
The RSV test detects the virus in the nasal and/or respiratory secretions of people who have been infected. Because detectable amounts of virus are shed in nasal secretions only for a few days after infection, the test should be carried out during this period. There are several methods for detecting the virus; the most widely used is the rapid RSV antigen test. This test can be done in outpatient settings, and results are available in about an hour. Alternatively, tests that take longer but are more sensitive can be used; results of these tests are usually available within a few days.
In some cases, viral culture (to increase the number of viral particles in the sample and therefore the sensitivity of the test) or molecular tests to detect the viral genome may be used. These two types of test have the advantage of identifying not only RSV but also other respiratory viruses that may be present. On the other hand, they are not available in all laboratories and take longer than rapid tests. This makes them less clinically useful for assessing an individual patient; they are more useful for identifying community infections or outbreaks in particular settings such as schools or nurseries.
How is the sample collected for testing?
The test is most often carried out on a nasal aspirate or wash. A small amount of saline is introduced into the nasal cavity and then gently suctioned out.
Alternatively, in some cases a nasopharyngeal swab may be taken, but this method has the disadvantage of reducing the amount of virus in the sample. A sterile, flexible swab is inserted through the nostril into the nasopharynx and gently rotated for a few seconds.
Does the test require any special preparation?
No special preparation is needed.
How is it used?
RSV testing is carried out during the season when this infection is most common, to help diagnose patients with symptoms of varying severity involving the lower respiratory tract. It is prescribed mainly for children aged 6 months to two years, older patients and patients with a weakened immune system, such as patients with existing lung disease and transplant recipients. Adolescents and the rest of the general population are not routinely tested, because most of them will have symptoms involving the upper respiratory tract, such as a runny nose, sneezing, cough, sore throat and fever.
The RSV test is also used to document the spread of RSV infection in the population. Because the infection is self-limiting in most cases, the aim of the health system is to contain and limit the spread of RSV so as to limit infection of at-risk patients. Treatment of RSV infection is mainly symptomatic, to reduce pain, fever and difficulty breathing. RSV testing is often combined with testing for flu viruses when both viruses are known to be circulating in the community.
Viral culture or genetic testing can be used to identify other viral infections that may cause clinical symptoms similar to RSV.
When is it requested?
The RSV test is prescribed during the cold months and in early spring. It is carried out in patients, usually children or older people, with a lower respiratory tract infection and symptoms such as difficulty breathing, severe cough, wheezing (especially in children), fever, headache and sore throat.
If flu has also been identified in the community, a flu test may also be requested to establish the cause of infection in a given person. When the cause of infection is unclear, tests for bacterial infections, such as a group A streptococcus test, may also be carried out.
What does the test mean?
If the RSV test is positive, the patient probably has an infection caused by this pathogen. A positive viral culture or genetic test can confirm the diagnosis. A positive RSV test does not, however, give any information about the duration or severity of the illness. Symptoms usually develop 4-6 days after infection.
A negative rapid RSV test may mean either that the infection is due to another pathogen or that the amount of virus was too low to be detected. A low viral load may be due to collecting too small a sample or to the secretions not containing enough virus to be detected by this method. Adults tend to have less virus in their secretions than children, and people who were infected several days earlier shed less virus than those infected more recently.
Is there anything else I should know?
Most RSV infections clear up in 2-3 weeks. People reinfected with different RSV strains tend to have milder symptoms than with the first infection. Because the symptoms are so mild, these reinfections are usually thought to be colds, are not diagnosed and are treated with home remedies.
1. Is there a blood test for RSV?
2. Is there a vaccine, like the flu vaccine, to prevent RSV infection?
3. Are antibiotics useful for RSV infection?
1. Is there a blood test for RSV?
There are serological tests that detect anti-RSV antibodies produced by the immune system. However, these tests can identify previous exposure to the virus but are not considered particularly clinically useful for diagnosing an active infection.
2. Is there a vaccine, like the flu vaccine, to prevent RSV infection?
Not at present. However, a great deal of research is being done in this area.
3. Are antibiotics useful for RSV infection?
No. RSV infection is caused by a virus, not a bacterium, so antibiotic treatment is not indicated. It may be useful only in the case of complications. There is a short-term drug treatment that is prescribed for high-risk patients. This treatment does not prevent or cure RSV infection but minimises the involvement of the lower respiratory tract, reducing the risk of hospital admission for these people. This type of immunotherapy may be given to babies in intensive care units while RSV infection is circulating. Premature babies are particularly susceptible to RSV infection.