Respiratory syncytial virus (RSV) basics

Respiratory syncytial (sin-SISH-uhl) virus, or RSV, is a respiratory virus that infects the lungs and breathing passages.

Healthy people usually experience mild, cold-like symptoms and recover in a week or two, but RSV can be serious, especially for infants and older adults.

baby with rsv infection

The cause of many colds and pneumonia

RSV can cause upper respiratory infections (such as colds) and lower respiratory tract infections (such as bronchiolitis and pneumonia). In children younger than 1 year of age, RSV is the most common cause of bronchiolitis, an inflammation of the small airways in the lung, and pneumonia, an infection of the lungs.

Almost all children will have had an RSV infection by their second birthday. When infants and children are exposed to RSV for the first time…

  • 25 to 40 out of 100 of them have signs or symptoms of bronchiolitis or pneumonia, and
  • 5 to 20 out of 1,000 will require hospitalization. Most children hospitalized for RSV infection are younger than 6 months of age.

Infants and children infected with RSV usually show symptoms within 4 to 6 days of infection. Most will recover in 1 to 2 weeks. However, even after recovery, very young infants and children with weakened immune systems can continue to spread the virus for 1 to 3 weeks.

People of any age can get another RSV infection, but infections later in life are generally less severe. Premature infants, children younger than 2 years of age with congenital heart or chronic lung disease, and children with compromised (weakened) immune systems due to a medical condition or medical treatment are at highest risk for severe disease. Adults with compromised immune systems and those 65 and older are also at increased risk of severe disease.

In the United States and other areas with similar climates, RSV infections generally occur during fall, winter, and spring. The timing and severity of RSV circulation in a given community can vary from year to year.

Also see: Whooping cough basics: Pertussis complications, diagnosis & treatment

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RSV brings lots of kids to the emergency room

A 2009 study, led by Florence Bourgeois, MD, MPH and Kenneth Mandl, MD, MPH, both of Children’s Division of Emergency Medicine and the Children’s Hospital Informatics Program at Children’s Hospital Boston, looked at acute respiratory illnesses in children aged 7 and younger, and found that patients infected with RSV had more than twice as many Emergency Department visits, and six times more hospitalizations than those infected with seasonal flu. RSV-related illnesses were also twice as likely to lead to additional primary care clinic visits and to antibiotic treatment.



The parents of children with RSV missed almost three times more workdays than parents of children with the flu, and parents of children under age 2 were nearly five times more likely to miss work when their child had RSV.

“RSV has been underappreciated,” says Bourgeois, who is also affiliated with Harvard Medical School. “There’s been disproportionate attention given to influenza, even though our data show morbidity to be very high from RSV. Based on our data, much more should be done in terms of prevention.”

RSV symptoms and care

Symptoms of RSV infection are similar to other respiratory infections. Illness usually begins 4 to 6 days after exposure (range: 2 to 8 days) with a runny nose and decrease in appetite. Coughing, sneezing, and fever typically develop 1 to 3 days later. Wheezing may also occur.

Also see: Cold, flu or allergy? How to tell the symptoms apart

In very young infants, irritability, decreased activity, and breathing difficulties may be the only symptoms of infection. Most otherwise healthy infants infected with RSV do not need to be hospitalized. In most cases, even among those who need to be hospitalized, hospitalization usually only lasts a few days, and full recovery from illness occurs in about 1 to 2 weeks.

Visits to a healthcare provider for an RSV infection are very common. During such visits, the healthcare provider will assess the severity of disease to determine if the patient should be hospitalized. In the most severe cases of disease, infants may require supplemental oxygen, suctioning of mucus from the airways, or intubation (have breathing tubes inserted) with mechanical ventilation.

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How RSV is spread

People infected with RSV are usually contagious for 3 to 8 days. However, some infants and people with weakened immune systems can be contagious for as long as 4 weeks. Children are often exposed to and infected with RSV outside the home, such as in school or childcare. They can then transmit the virus to other members of the family.

RSV can be spread when an infected person coughs or sneezes into the air, creating virus-containing droplets that can linger briefly in the air. Other people can become infected if the droplet particles contact their nose, mouth, or eye.

According to a University of Rochester Medical Center study published in 2009 in New England Journal of Medicine, all children are infected with RSV during their first two years of life, and may be repeatedly infected thereafter, sometimes within months. This study found that RSV causes three times as many hospitalizations as does influenza and parainfluenza in children under 5 years of age.

Infection can also result from direct and indirect contact with nasal or oral secretions from infected people. Direct contact with the virus can occur, for example, by kissing the face of a child with RSV. Indirect contact can occur if the virus gets on an environmental surface, such as a doorknob, that is then touched by other people. Direct and indirect transmissions of virus usually occur when people touch an infectious secretion and then rub their eyes or nose.

RSV can survive on hard surfaces such as tables and crib rails for many hours, and the virus typically lives on soft surfaces such as tissues and hands for shorter amounts of time.

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Preventing Respiratory Syncytial Virus outbreaks

Researchers are working to develop RSV vaccines, but none is available yet. However, there are steps that can be taken to help prevent the spread of RSV. Specifically, people who have cold-like symptoms should

  • Cover their coughs and sneezes
  • Wash their hands frequently and correctly (with soap and water for 20 seconds)
  • Avoid sharing their cups and eating utensils with others
  • Refrain from kissing others

In addition, cleaning contaminated surfaces (such as doorknobs) may help stop the spread of RSV.

Parents should pay special attention to protecting children at high risk for developing severe disease if infected with RSV. Such children include premature infants, children younger than 2 years of age with chronic lung or heart conditions, and children with weakened immune systems.

Ideally, people with cold-like symptoms should not interact with children at high risk for severe disease. If this is not possible, these people should carefully follow the prevention steps mentioned above and wash their hands before interacting with children at high risk. They should also refrain from kissing high-risk children while they have cold-like symptoms. When possible, limiting the time that high-risk children spend in child-care centers or other potentially contagious settings may help prevent infection and spread of the virus during the RSV season.

A drug called palivizumab (“pah-lih-VIH-zu-mahb”) is available to prevent severe RSV illness in certain infants and children who are at high risk. The drug can help prevent development of serious RSV disease, but it cannot help cure or treat children already suffering from serious RSV disease and it cannot prevent infection with RSV. If your child is at high risk for severe RSV disease, talk to your healthcare provider to see if palivizumab can be used as a preventive measure.



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