Respiratory Syncytial Virus (RSV) is a highly common respiratory pathogen that causes infections of the lungs and breathing passages in people of all ages. Almost every child will have been infected with RSV at least once by the age of two. While the virus is known for causing significant respiratory illness in infants and older adults, it can also infect individuals without producing any noticeable signs or symptoms. This silent infection means a person may be infected and contagious without ever feeling sick. The presentation of an RSV infection is highly dependent on a person’s age and their prior exposure to the virus.
The Likelihood of Silent Infection
Asymptomatic RSV infection is a frequent occurrence, particularly among individuals with a mature immune system. Studies have found that over 40% of RSV infection episodes can occur without the person reporting any cold or flu-like symptoms. This absence of symptoms is most common in healthy adults and older children who have encountered the virus previously. Their immune memory allows them to clear the infection before it can trigger a significant inflammatory response.
The probability of experiencing a symptomless RSV infection increases with age and is associated with having a lower peak viral load. When a person is reinfected, their neutralizing antibodies and T-cells quickly mitigate the viral spread within the respiratory tract. This robust immunity prevents the infection from progressing to the stage that causes the tissue damage and inflammation responsible for symptoms. In contrast, infants experiencing their first RSV infection rarely remain asymptomatic, leading to a much higher likelihood of symptomatic illness.
Spreading RSV Without Symptoms
An individual infected with RSV can still shed the virus and transmit it to others, even if they never develop symptoms. Viral shedding is the release of infectious virus particles from the respiratory tract into the environment through breathing, talking, or sneezing. This means people who feel healthy can contribute to the spread of the virus within a community.
While transmission is possible from asymptomatic carriers, symptomatic individuals generally shed the virus for a longer duration and in higher concentrations. Symptomatic individuals may shed the virus for an average of 13 days, whereas asymptomatic shedding typically lasts around one week. Even with a lower viral load, asymptomatic spread makes containment difficult, especially in high-risk settings like daycare centers and hospitals. The silent movement of the virus increases the risk of exposure for vulnerable groups, such as premature infants and older adults, who face the highest risk of severe disease upon infection.
Understanding Typical RSV Illness
When RSV infection causes symptoms, its presentation can vary widely, ranging from mild cold symptoms to severe lower respiratory tract disease. In most healthy adults and older children, the infection manifests as a mild upper respiratory illness, which may include a runny or stuffy nose, sore throat, sneezing, and a low-grade fever. These mild symptoms usually appear four to six days after exposure and typically resolve within one to two weeks.
However, the infection can progress to cause more serious illness when it moves into the small air passages of the lungs. In infants and the elderly, RSV is a frequent cause of bronchiolitis, the inflammation and obstruction of these small airways, or pneumonia. Signs of a severe infection include wheezing and difficulty breathing, which may manifest as rapid or shallow breaths.
Parents should be watchful for signs of distress in infants, such as short, shallow, or rapid breathing, or if the skin and chest muscles pull inward with each breath. Other concerning signs include unusual tiredness, lethargy, or a significant decrease in feeding. Medical attention is advised if a person, especially a young child or an older adult, experiences worsening symptoms, difficulty breathing, or signs of dehydration.