Our findings indicate that RSV causes a substantially greater burden in young children and their families than influenza. ARIs caused by RSV result in more than twice as many ED visits and 6 times as many hospitalizations compared with ARIs related to influenza. RSV infections are also twice as likely to result in additional primary care clinic visits and in antibiotic treatment. The parents of children with RSV miss almost 3 times more workdays than parents of children with influenza, and those with children younger than 2 years are nearly 5 times more likely to miss work when their child has RSV. Because the economic burden of childhood illnesses is largely driven by lost caregiver wages,33–35
prevention and control approaches that address RSV as well as influenza among young children are likely to be most cost-effective.
Detailed guidelines that summarize recommendations for the containment of influenza infection are published every year by the Influenza Division of the Centers for Disease Control and Prevention.36,37
These include well-developed influenza vaccination policies, guidelines for the use of antiviral medications, and control measures for specific settings such as child care facilities and nursing homes. Similar strategies are not available for the containment of RSV. Despite many years of vaccine research, prevention measures for RSV remain limited to immunoprophylaxis of children at high risk.38,39
A better understanding of the contribution of RSV to the yearly burden of winter respiratory infections will serve to inform the development of prevention initiatives and to identify at-risk populations and cost-effective policies.
Although we provide new data on resource use in the clinical and outpatient settings, the rates of viral infection are consistent with previous studies, lending external validation to our methods. Similar to our laboratory-confirmed positivity rates of 11.2% for influenza and 23.6% for RSV infections among children who were aged ≤7 years and had ARIs, published estimates of viral prevalence among children range from 6% to 16% for influenza21,40–43
and 20% to 48% for RSV40–42
during seasons and among patient populations that are different from the ones studied here. Poehling et al21
reported ED visit rates for influenza of 6 and 27 per 1000 children aged 0 to 4 years during 2 influenza seasons, comparable to the rate in this study of 10.2 per 1000 children. In a recent study by Hall et al,25
ED visit rates for RSV illnesses were found to range from 22 to 32 for children aged 0 to 4 years, similar to the rate of 21.5 per 1000 children reported in this study. Hospitalization rates reported in the literature are also similar to ours, ranging from 0.6 to 1.8 per 1000 children5,7,8,17,18,20,42,43
for influenza infections and 3.0 to 5.8 per 1000 children for RSV illnesses6–8,18,25,42,44
among children in similar age groups.
Additional support for the accuracy of our findings is the similarity in the rates that we report for the state and national populations. We calculated estimates for the Massachusetts population by using public health data, which include counts of all visits to Massachusetts EDs.28
To obtain national estimates, we used a survey conducted by the National Center for Health Statistics, which collects information on national samples of visits to US EDs and allows computation of national estimates on the basis of proportional weights assigned to surveyed visits.45
These 2 approaches yielded very similar results with slightly higher estimates for the national rates but none appreciably different from the state-level figures.
The methods used in this study—using cohort data in combination with public health and national survey data—may serve as a model for estimating the disease burden of other infectious and noninfectious illnesses. A similar approach has been used in studies published by the New Vaccine Surveillance Network, which conducts population-based surveillance of ARIs among children who are younger than 5 years.21,25
In those studies, surveillance is conducted in 3 counties in the United States, and population estimates of virus-specific infections are obtained by using local market share rates, US Census figures, and National Hospital and Ambulatory Medical Care Survey data.
Our study has several limitations. In the resource-use cohort, our enrollment rate was high, but it is possible that a nonparticipation bias affected our resource-use rates. It is also possible that there were inaccuracies in the information provided by parents, which we were not able to verify; however, it is unlikely that there was a systematic bias toward either RSV or influenza infection. Our results are based on a patient population from a single institution, possibly limiting the generalizability of our findings. We assumed that results of virologic testing from our sample were applicable to all patients who were treated in the ED with ARIs. This assumption is supported by comparable rates found in our prospective cohort and from published reports.21,40–43
To extrapolate to the state-level population, we assumed that the other state EDs had similar rates of visits for ARIs as well as influenza and RSV infections. For national estimates, we assumed that the rate of influenza and RSV infections was the same among ARI visits as in our study population. The use of National Hospital and Ambulatory Medical Care Survey data and this method, however, is consistent with the approach used in a previous study that examined national rates of ED visits for influenza.21
Finally, we may have underestimated the total burden of influenza and RSV by excluding visits with viral co-infections, although there were similar rates of co-infections among patients with influenza and RSV. None of these limitations should impede our main objective to make relative comparisons between influenza- and RSV-associated health care use. In fact, the total burden of RSV may have been underestimated in this study, because the RSV season may begin as early as November and we chose to include only December through April in our definition of the winter season; however, a recent article reported the medical onset of yearly RSV outbreaks as December 1.25