Influenza-related deaths and hospitalizations in children have been nationally notifiable since 2004.  On the other hand, no Respiratory Syncytial Virus (RSV) surveillance system exists nationally or in the state of Wisconsin, despite several studies finding that RSV is associated with more deaths in infants and more hospitalizations in children under age 5 than influenza viruses. With the development of an RSV vaccine on the horizon, it is time to strengthen surveillance efforts to expedite the release of a safe and effective vaccine to target populations.

RSV-related mortality and inpatient and outpatient burden is not well-defined due to the lack of surveillance; however, multi-site studies have estimated RSV accounts for roughly 57,000 hospitalizations, 500,000 ER visits, and 1.5 million outpatient visits for bronchiolitis and pneumonia annually in children under 5 (See Table below for comparison to influenza). Risk factors for RSV hospitalization included male sex, chronic underlying medical conditions, lower socioeconomic status, and smoke exposure, while breastfeeding was found to be a protective factor (Hall et al., 2009).  In addition to the burden caused by acute RSV infection, infants and toddlers that develop RSV bronchiolitis or pneumonia may suffer from wheezing, asthma, and other pulmonary dysfunction for years after the initial illness.

Even less understood is the burden of RSV in adults, partially because RSV antigen detection is insensitive in adult populations. Recent studies suggest that RSV morbidity and mortality is under-recognized among older adults, immunocompromised individuals, and adults with cardiopulmonary disease due to the diagnostic challenges in these populations (Branche & Falsey, 2015).  In pediatric populations, however, laboratory diagnosis is uncomplicated in both outpatient and inpatient settings, and hospital-based and public health surveillance is currently possible.

This summer, I am completing a rotation at the Bureau of Communicable Disease in Wisconsin’s Department of Health and Human Services, working on a project with a CDC epidemiology field officer to describe the rates of various respiratory viruses, including RSV, among children hospitalized for respiratory illnesses in Wisconsin.  I have been astonished by the preliminary results, which show that very few viral respiratory illnesses were attributable to influenza (roughly 5%). The most common virus among children hospitalized for viral respiratory conditions has been RSV, which accounted for over a third of infections, followed by coronavirus and adenovirus.  Because no surveillance system has been implemented to track RSV-related hospitalization in Wisconsin, I am abstracting the data from medical records, which is an arduous and time-consuming task.  I am hopeful, however, that our results will help Wisconsin move forward and become one of the first states to require RSV reporting.  Influenza surveillance efforts have facilitated improved vaccination rates in many populations, preventing thousands of deaths and hospitalizations. Similarly, RSV surveillance efforts would position Wisconsin to effectively combat this significant cause of childhood morbidity and mortality when the RSV vaccine is available.

Table. Estimated Annual Burden of Influenza and RSV in Children*

Influenza RSV
Hospitalization rate in Children under 5 years (per 100,000) 95 271
Mortality rate in infants (per 100,000) 6.7 8.4

*Abstracted from CDC, Hall et al. (2009), and Fleming, Pannell, and Cross (2005)


By: Elizabeth Stein, MD, MS