RSV outbreaks, strains vary across the United States

Issue: January 2011

Respiratory syncytial virus is the cause of 50% to 90% of hospitalizations for bronchiolitis, 5% to 40% of hospitalizations for pneumonia and 10% to 30% of hospitalizations for croup, according to a recent presentation.

Gary Goodman

According to Gary Goodman, MD, medical director of the pediatric ICU and hospitalist service at Children’s Hospital of Orange County at Mission, in Mission Viejo, Calif., the history of respiratory syncytial virus (RSV) dates back to the 1840s, with clinical descriptions of infantile pneumonias that may have been caused by RSV. Goodman spoke during a CME seminar supported by MedImmune.

The virus, which enters the upper respiratory tract and replicates in the nasopharynx, may spread to the lower respiratory tract in 1 to 3 days and cause inflammation of the small airway and airflow obstruction. The incubation period is usually 3 to 6 days, and children are contagious for 3 to 8 days, unless they are immunosuppressed.

“The virus manifests as upper respiratory tract infections, such as rhinitis and otitis media, or lower respiratory tract infections, such as croup, bronchiolitis or pneumonia,” Goodman said. “It may manifest as apnea in premature infants.”

Approximately 70% of infants are infected with RSV in the first year of life, and almost all are symptomatic, he said. About 20% of the cases result in lower respiratory tract infections. Re-infection is common, although subsequent infections tend to be more mild. Hospitalization related to RSV most commonly occurs in children aged up to 2 years who have congenital heart disease or chronic lung disease.

During RSV season, the outbreaks are generally localized; the differences in disease onset, peak and offset vary within short distances, and the strains between adjacent communities often vary in the same season. About 80% of hospitalizations caused by RSV occur between November and April, and peak activity is in January and February. The average season lasts 22 weeks.

“Globally, RSV is the most common cause of childhood acute lower respiratory infections and a major cause of admission to the hospital as a result of these infections,” Goodman said.

Worldwide, an estimated 34 million new episodes of RSV-related acute lower respiratory infections in children occurred in 2005. At least 3.4 million of these episodes required hospital admission, and an estimated 66,000 to 199,000 children aged younger than 5 years died from RSV-associated acute lower respiratory infections.

Disclosure: Dr. Goodman has a direct financial interest in palivizumab. He is a paid consultant for MedImmune.

Jeffrey S. Kahn

RSV continues to be a major challenge for both the medical and scientific communities. Unfortunately, the clinical approach to the child infected with RSV has essentially remained the same since the mid-1950s when the virus was discovered. Other than supportive care, there are few therapeutic options. Antiviral therapy with ribavirin is controversial and of limited effectiveness, at best. Several attempts to develop an RSV vaccine have failed, including a formalin-inactivate vaccine, tested in the 1960s, that led to more severe RSV disease in vaccine recipients than controls. There are a few promising RSV candidate vaccines on the horizon, though none that confer complete protective immunity. The epidemiology of RSV is complex and dynamic. There are two subgroups of RSV, A and B, and several strains of both subgroups circulate during each seasonal epidemic. Unlike influenza in which three (or more) strains circulate worldwide, RSV strains differ from location to location. Strain variability, both on a temporal and geographic level, is yet another obstacle for the development of an RSV vaccine. A single universal vaccine to protect against all subgroup A and B strains may be an unrealistic goal.

— Jeffrey S. Kahn, MD, PhD
Director, Infectious Diseases, Department of Pediatrics, UT Southwestern Medical Center
Disclosure: Dr. Kahn has no direct financial interest in any of the products mentioned in this article nor is he a paid consultant for any companies mentioned.