Respiratory syncytial virus (RSV) testing is usually used during the RSV season to help diagnose the infection in people with moderate to severe symptoms and lower respiratory tract infection. It is primarily ordered for infants between the ages of 6 months and 2 years, the elderly, and those with weakened (compromised) immune systems, such as those who have pre-existing lung disease or who have had an organ transplant. Photo source: CDC, Craig Lyerla

RSV testing is not routinely performed for older children and the rest of the general population 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 may be used to document and track the spread of RSV in the community. Public health efforts are focused on containing and preventing the spread of RSV as much as possible to minimize the chance of spreading the virus to high-risk people. Those with mild symptoms may only be tested for RSV if it is necessary to help track its spread. Influenza testing may also be done if both viruses are known to be present in the community.

A few types of RSV tests are available for use:

• Rapid RSV antigen testing—this is by far the most common test. Rapid RSV antigen tests are frequently performed on-site, in the healthcare practitioner's office or the emergency room, with most results available within an hour. In some cases, the sample may be collected and sent to a laboratory for a more sensitive testing method. Results of these RSV tests are usually available the same day.
• RSV RT-PCR—this is a molecular test that detects the genetic material of the virus. It is generally more sensitive than antigen testing or viral culture. It may be used in conjunction with other tests to detect other viral infections that may cause signs and symptoms similar to RSV.
• Viral cultures—these are used to grow and identify the RSV virus. Viral cultures can identify the RSV virus and other respiratory viruses that may be present. Availability of viral cultures is decreasing as most laboratories adopt molecular assays to detect viral infections. Viral cultures are costly and more difficult to perform and take days to provide a result, which makes them less clinically useful for evaluating an individual.

Other tests that may be done in conjunction with RSV testing include:

• Influenza tests
• Group A strep test, to detect the streptococcal bacteria that causes strep throat

RSV tests are ordered almost exclusively during "cold and flu season" – late fall to early spring. They are ordered when someone, usually an infant or elderly person, has a serious lower respiratory infection and signs and symptoms, such as:

• Wheezing
• Severe coughing
• Rapid breathing (primarily in infants)
• Fevers
• Headaches
• Runny, stuffy nose
• Sore throat

Testing must be done within the first few days of infection and the appearance of signs and symptoms because detectable amounts of virus are usually shed during the early phase of infection.

When RSV has already been identified in the community, a healthcare practitioner may order a rapid RSV test to confirm the suspected diagnosis in a symptomatic person.

If an RSV test is positive, then it is likely that the person has a respiratory syncytial virus infection. A positive test can also confirm the presence of RSV in the community. A positive RSV test cannot, however, tell a healthcare practitioner how severe a person's symptoms are likely to be or how long ago the patient was infected. Symptoms usually appear 4-6 days after infection.

Negative RSV tests may mean that the person tested has something other than RSV or that there is not sufficient virus in the sample to be detected. This may be due to either a poor specimen collection or because the person is not shedding detectable levels of virus into his or her respiratory secretions. Adults tend to shed less virus than infants do, and those who have had RSV for several days will shed less than those with a more recent infection.

Most RSV infections will resolve within 1 or 2 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 with over-the-counter cold remedies for symptom relief.