What is being tested?
RSV testing is used to detect respiratory syncytial virus, the most common cause of lower respiratory tract infections in infants around the world. RSV tends to be seasonal, causing community epidemics in young children, older adults, immunocompromised people and those with pre-existing lung disease. Typically the season begins in late autumn and disappears in early spring. Affected people may have symptoms such as severe coughing, wheezing, difficulty breathing and high fevers. For many, symptoms may be no worse than a common cold, but RSV can be life-threatening for the very young, the immunocompromised, those with pre-existing lung disease or the elderly.
RSV testing detects virus that is being shed in the respiratory/nasal secretions of someone who is infected. Since detectable amounts of virus are usually only shed for the first few days of an infection, most testing must be done during this time period. There are several methods to test for the virus, including rapid RSV antigen testing, detection of RSV nucleic acids by PCR, immunofluorescent antibody (IFA) tests and viral culture. Rapid RSV antigen tests are often performed in the doctor’s office or the emergency room, with most results available within an hour. However, rapid antigen testing lacks sensitivity unless performed in a situation where the likelihood of infection is already high (for example, testing an infant with typical symptoms during an epidemic). In other situations, the sample may be collected and sent to a laboratory for a more sensitive and specific testing method such as PCR or IFA tests. In many laboratories the test for RSV is combined with tests for multiple respiratory viruses. Results of these RSV tests are usually available the same day.
Viral culture (to grow the RSV virus) is not routinely performed by laboratories. This is because RSV is difficult and slow to culture.
How is it used?
RSV testing is usually used during the RSV season to help diagnose people who have moderate to severe symptoms and lower respiratory tract involvement. It is primarily ordered for infants (between the ages of six months and two years), the elderly and those people with compromised immune systems, such as those who have pre-existing lung disease or who have had an organ transplant. Older children and the rest of the general population are not routinely tested or diagnosed because most of them will experience only relatively mild upper respiratory infections with symptoms such as a runny nose, sneezing, coughing, sore throat and fever.
RSV testing is also used to document and track the spread of RSV in the community. Since most cases of RSV are self-limiting, community health efforts are focused on containing and preventing the spread of RSV as much as possible to minimise the chance of spreading the virus to high-risk patients. Treatment of RSV is primarily supportive, minimising pain and fever and easing breathing. Those with mild symptoms may only be tested for RSV if it is necessary to help track its spread. RSV testing is frequently ordered along with tests for other respiratory viruses such as influenza. Combined testing helps narrow down the cause of the respiratory infection faster.
When is it requested?
RSV tests are ordered almost exclusively during the cold and flu season – late autumn to early spring. They are ordered when someone, usually an infant or elderly person, presents to their doctor with a lower respiratory infection and symptoms such as wheezing, severe coughing, rapid breathing (primarily in infants), fevers, headaches, a runny stuffy nose and a sore throat.
When RSV has already been identified in the community, the doctor may order a rapid RSV test to confirm the suspected diagnosis in the symptomatic patient. If influenza is also in the community, RSV testing may be ordered along with influenza testing to determine which virus the patient has. The doctor may also order bacterial tests, such as a strep test (to check for group A streptococcus, the bacteria that cause strep throat), when the cause of the infection is unclear.
What does the result mean?
If a rapid RSV test is positive it is likely that the person has respiratory syncytial virus. A positive viral culture or genetic viral test can confirm the presence of RSV in the community. However, a positive RSV test cannot show how severe a patient’s symptoms are likely to be or how long ago they were infected. Symptoms usually appear from four to six days after infection.
Negative rapid RSV tests may mean that your symptoms are due to something other than RSV or that there is not sufficient virus in the specimen to allow it to be detected. This may be due to either a poor specimen collection or because you are not shedding detectible levels of virus into your respiratory secretions. Adults tend to shed less of the virus than infants and those people who have had RSV for several days will shed less than those with a more recent infection.
Is there anything else I should know?
Most RSV infections will go away within one or two weeks. People can be re-infected with different strains of RSV from year to year, although subsequent infections tend to be less severe than the first/primary infection. Since most RSV infections are mild, symptoms from these re-infections are usually attributed to a cold. These cases of RSV are usually not formally diagnosed and are often treated by the person themselves with over-the-counter cold remedies for symptom relief.
There are blood tests for RSV antibodies – the immune system’s response to the virus. These tests can detect previous exposure to RSV, but they are not usually considered clinically useful for diagnosing an active case of RSV.
Not currently, although it is considered a high priority by researchers.
No, RSV is due to a virus – not a bacteria – so antibiotic therapy is not indicated or helpful.
In the vast majority of cases RSV is treated only symptomatically. There is one antiviral that may be used in selected severely ill hospitalised patients. There is also a drug available that may be given to neonates in the intensive care nursery to protect them during RSV season. Premature infants can be especially vulnerable to RSV.
Washing hands and covering coughs and sneezes are very important in preventing the spread of respiratory viruses such as RSV. Infected children and adults should stay away from child-care centres, school and vulnerable people such as the elderly and immunocompromised.
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