Vaccine 28 (2010) 4913–4919
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/vaccine
High costs of influenza: Direct medical costs of influenza disease in young
Gerry Fairbrothera,∗, Amy Cassedyb, Ismael R. Ortega-Sanchezc, Peter G. Szilagyid,
Kathryn M. Edwardse, Noelle-Angelique Molinaric, Stephanie Donauerb,
Diana Hendersonf, Sandra Ambrosed, Diane Kente, Katherine Poehlingg,
Geoffrey A. Weinbergd, Marie R. Griffine, Caroline B. Halld, Lyn Finellic,
Carolyn Bridgesc, Mary Allen Staatf, the New Vaccine Surveillance Network (NVSN)c
aHealth Policy and Clinical Effectiveness, Cincinnati Children’s Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229, United States
bDivision of Biostatistics and Epidemiology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, United States
cNational Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, GA, United States
dSchool of Medicine and Dentistry, University of Rochester, Rochester, NY, United States
eSchool of Medicine, Vanderbilt University, Nashville, TN, United States
fInfectious Diseases, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, United States
gPediatrics, Epidemiology and Prevention, Wake Forest University, Winston-Salem, NC, United States
a r t i c l ei n f o
Received 30 September 2009
Received in revised form 3 May 2010
Accepted 16 May 2010
Available online 31 May 2010
a b s t r a c t
This study determined direct medical costs for influenza-associated hospitalizations and emergency
department (ED) visits. For 3 influenza seasons, children <5 years of age with laboratory-confirmed
influenza were identified through population-based surveillance. The mean direct cost per hospitalized
child was $5402, with annual cost burden estimated at $44 to $163 million. Factors associated with high-
cost hospitalizations included intensive care unit (ICU) admission and having an underlying high-risk
condition. The mean medical cost per ED visit was $512, with annual ED cost burden estimated at $62 to
$279 million. Implementation of the current vaccination policies will likely reduce the cost burden.
© 2010 Elsevier Ltd. All rights reserved.
Disease burden attributed to the influenza virus is substantial
and results in excess hospitalizations and emergency department
(ED) visits for children [1–4]. Although robust estimates of the
total hospitalization burden exist , reported mean influenza-
related hospitalization costs vary widely for both children alone
pitalizations ranged from $3521 , to $13,446 . The methods,
populations studied, and the results differ greatly, with the lowest
estimates using ICD-9-CM codes  for the diagnosis of influenza
rather than laboratory-confirmed influenza, and the highest esti-
nization Practices; NVSN, New Vaccine Surveillance Network; ICU, intensive care
unit; IQR, interquartile range; ARI, acute respiratory infection.
?The contents of the manuscript are solely the responsibility of the authors and
do not necessarily represent the official views of the Center for Disease Control.
∗Corresponding author. Tel.: +1 513 636 0189; fax: +1 513 636 0171.
E-mail address: email@example.com (G. Fairbrother).
mates using laboratory-confirmed influenza cases from tertiary
care centers that included greater proportions of children with
complex medical conditions [7,8].
The cost of influenza-related ED visits has received less atten-
population-based settings. One study reported an estimated mean
ago . While the overall costs for ED visits are reported to be
small compared to inpatient services, far more ED influenza visits
Moreover, major gaps in our knowledge about the factors asso-
ciated with high costs remain. Studies have shown that a small
number of children often account for a disproportionate share of
medical care expenditures [10–12]. Mean influenza cost estimates
may be influenced by children with complex conditions requiring
high levels of care. Indeed, studies have noted higher costs in older
children and in children with high risk conditions [6,8,9]. How-
ever, the specific factors associated with high influenza-related
costs need additional study. A better understanding of the factors
associated with the direct medical costs of influenza can support
0264-410X/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
G. Fairbrother et al. / Vaccine 28 (2010) 4913–4919
the current efforts toward more effective control of influenza and
thereby reduce costs associated with influenza illness.
We assessed influenza costs using a multi-site, population-
based New Vaccine Surveillance Network (NVSN). Active inpatient
and ED surveillance for acute respiratory infections (ARI) identi-
fied children with laboratory-confirmed influenza at the 3 NVSN
sites. We examined the direct medical costs in children less than 5
years of age hospitalized or evaluated in the ED during 3 consec-
utive influenza seasons. We also evaluated factors associated with
2.1. Study design and population
The design and methods of the NVSN active population-based
surveillance project have been previously described [4,13–17]. For
this study, 3 seasons of data from the inpatient and ED surveil-
lance were analyzed (2003–2004, 2004–2005, and 2005–2006)
from three counties in the US which contain the cities of Nashville,
cared for >95% of hospitalized children in their respective counties,
while the surveillance EDs at each county cared for a variable pro-
portion of the county’s pediatric ED visits: 30% in Nashville, 60% in
were enrolled within 48h of admission, Sunday through Thursday.
In the ED, children were systematically enrolled at each site: 3–4
days per week in Nashville and Rochester (rotating days) and every
fourth day in Cincinnati. Children admitted to the hospital through
the ED were categorized as hospitalized and all costs from both
sources were combined.
Children eligible for enrollment were <5 years of age, had
symptoms of an acute respiratory infection or fever, and were res-
idents of the active surveillance counties. Children were excluded
if they had fever and neutropenia associated with chemother-
apy, were hospitalized in the prior 4 days, were transferred from
another surveillance hospital, or had symptoms for greater than 14
Demographic, medical, and social histories were obtained by
standardized interviews of the parents or guardians. Clinical lab-
oratory evaluations, hospital course, and discharge diagnoses
were obtained from hospital and ED records. High-risk med-
ical conditions for influenza complications were recorded and
included asthma and reactive airways disease, chronic lung con-
ditions, cardiac disease, long-term salicylate therapy, sickle cell
disease, immunologic disorders, kidney disease and chronic renal
dysfunction, genetic metabolic syndromes, diabetes, neurological
disorders, and other chronic diseases . Children were consid-
ered premature if their parents reported that the child had been
born more than 4 weeks early.
Nasal and throat swabs were collected from each enrolled child
for influenza culture and reverse transcriptase polymerase chain
reaction (RT-PCR) testing. A child was considered influenza posi-
tive if either the viral culture or two independent RT-PCR tests on
the same specimen were positive . During 2003–2005, respira-
tory syncytial virus (RSV) cultures and RT-PCR testing were also
Cost and physician fee charge data were gathered from the
accounting databases at each participating hospital. Although the
billing source for each site varied, each contained similar data
lected for each child; a physician from each of the 3 sites (MAS,
PS, KE) sorted costs into the following 5 general summary cat-
egories following the typology of an earlier study: diagnostics,
therapeutics, room costs, medical supplies and physician services
. Department-specific cost-to-charge ratios that were available
from hospitals were used to adjust these medical costs. Cost-to-
charge ratios were not available for physician fees. To avoid issues
for physician services were estimated using gross physician fees
[19,20]. For a sensitivity analysis and projections, physician fees
were later adjusted using a generic cost-to-charge ratio . The
costs for inflation converted to constant 2006 dollars.
Data obtained from the hospital accounting databases were
merged with the NVSN database to develop a comprehensive
dataset which included demographic, medical, and cost data. Data
hospitalizations, children were grouped into 2 categories. If direct
medical costs were in the top 10th percentile, the hospitalization
was considered to be high cost , while those hospitalizations
with costs in the lower 90th percentile were considered non-high
cost. Pediatricians who categorized expenditures for all hospital-
izations (MAS, PS, KE) also reviewed the medical records of the
high cost children to determine to what extent their costs could be
attributed to influenza.
2.2. Institutional Review Board Approval
Informed written consent was obtained from the par-
at the Centers for Disease Control and Prevention (CDC) and at
each site approved the study. Neither the treating clinicians nor
parents/guardians were informed of the research virology results
during the hospitalization or ED visit.
2.3. Statistical analyses
We summarized direct medical costs using univariate anal-
ysis and calculated means, standard deviations, medians, and
interquartile distributions. We used the Kruskal–Wallis test to
determine group differences in the median total costs and length
lyze the relationships and characteristics associated with high cost
and non-high cost children. A two-sided P-value of <0.05 indicated
statistical significance. We conducted all statistical analyses in SAS
9.1 (SAS Institute Inc. Cary, NC).
We estimated the total cost burden of medically attended
influenza (hospitalizations and ED visits) using mean costs from
this study, and rates of hospitalizations and ED visits from an ear-
lier study reporting on rates from the same NVSN sites as in the
attributable to influenza for years 2000–2004 varying between 0.4
per 1000 children (95% confidence interval 0.2–0.6 per 1000) and
1.5 per 1000 children (95% confidence interval 1.2–1.9 per 1000)
. ED visit rates, which were available for 2 of the 4 years, were
6 per 1000 children (95% confidence interval 4–9 per 1000) for
2002–2003 and 27 per 1000 (95% confidence interval 22–33 per
1000) for 2003–2004. In calculations, in order to account for varia-
tions in burden across seasons, we used a range for hospitalization
rate of 0.4–1.5 per 1000 children, with 95% confidence interval of
per 1000 children with 95% confidence interval from 4 to 33 per
1000 children . These rates are consistent with those reported
in other studies, and most published rates fall within these confi-
dence bands [3,14,22–24]. To estimate the total national influenza
burden, we multiplied the influenza attributed ED visit and hospi-
talization rates from the prior study  by the average number of
sus Bureau estimates for 2003 through 2006 . To estimate cost
burden for these children, we multiplied the influenza attributed
G. Fairbrother et al. / Vaccine 28 (2010) 4913–4919
Characteristics of hospitalized and emergency department influenza-positive children, 2003–2006.
Hospitalized (n=188) Emergency department (n=202)
Presence of risk factor for influenzaa
Age in months
<6 months of age
≥6 months of age
aAccording to ACIP Influenza Recommendations, April, 2003 .
*Significance of differences between characteristics of hospitalized and ED only children.
ED visit and hospitalization rates calculated as described above by
the mean cost per child with laboratory-confirmed influenza.
NVSN surveillance during the 3 study years detected a total of
436 influenza-positive cases in the hospital and ED settings com-
bined. Due to one hospital closing and another changing its billing
policies, we were unable to obtain cost data for 35 patients (8%).
Deviations from the enrollment protocol resulted in the exclu-
sion of 11 cases (2.5%) from the Cincinnati site. These 11 cases
did not differ from other enrolled children from Cincinnati with
respect to race, gender, or insurance status, but were more likely
to be >6 months of age (P=0.02). Overall, results were similar with
these children included and excluded. Of the 390 cases (89%) with
laboratory-confirmed influenza and available cost data, 188 were
hospitalized, while 202 were seen only in the ED. Compared to
children who were hospitalized, children seen in the ED (and not
subsequently hospitalized) were more likely to be black, older, and
have public insurance (Table 1).
3.1. Influenza-related hospitalization and emergency department
The mean direct medical cost per influenza-associated hos-
pitalization was $5402, with a median of $3347 (Table 2). Of
hospitalization costs, 60% of the total direct medical costs were due
recovery room costs, as well as facilities-related costs incurred in
the ED visits. Physician fees accounted for another 20% of the total
hospital costs (Table 2).
a median cost of $409. The largest components of ED costs were
physician fees ($233, or 46% of the total costs) and ED room costs
($215, or 42% of the total costs).
Direct medical cost for hospitalized and emergency department influenza-positive patients, 2003–2006.
Hospitalizations (n=188)Emergency department (n=202)
Room costs and ED
Operating and recovery
$2$186 $64 (0–332)<1 $0(0–0)
Total average costs $5402100 $3347(2354–4862) $512 100$409(333–557)
G. Fairbrother et al. / Vaccine 28 (2010) 4913–4919
Hospital costs and total LOS for 188 hospitalized children with laboratory-confirmed influenza, 2003–2006.
Hospital costs Length of stay (total LOS)
P value Total cost Percent of costMeanMed (IQR)
Total bed days Percent total bed days
High risk condition
aP-value refers to comparison of population medians (Kruskal–Wallis).
bRSV status is not known for 32 children. These children are not included in the cost for RSV co-infection.
G. Fairbrother et al. / Vaccine 28 (2010) 4913–4919
Mean cost, rates, national burden, and national cost for influenza for children <5 years of age.
Hospital Emergency department
Mean cost per child (2003–2006)
Rate per 1000a
National burden (# per year)
National cost (in millions)
a2000–2004 for hospital; 2002–2004 for emergency department.
3.2. Factors associated with influenza-related hospitalization and
Table 3 displays the factors associated with higher costs among
the 188 hospitalized children. An ICU stay generated significantly
greater costs than a non-ICU stay. No other factors were significant
at the patient level. Despite the fact that the small number of chil-
dren in the ICU had substantially higher individual costs, children
not in the ICU accounted for 62% of the total population-wide med-
no significant differences in mean or median costs by age, children
<6 months of age accounted for 52% (Table 1) of the influenza-
related hospitalizations and 45% of the total costs (Table 3). RSV
co-infection was found in 17% of the children with influenza in the
first 2 seasons (when testing was done), 18% in 2003–2004, and 9%
in 2004–2005; there was no significant difference in the mean cost
of children with and without RSV co-infection.
3.3. Characteristics of high-cost hospitalizations (top 10% of costs)
Overall, there were 20 high-cost hospitalizations, ranging from
$8337 to $95,524 (data not shown). Chart reviews revealed that
17 (85%) of the high-cost hospitalizations appeared to be clearly
influenza related: 11 (55%) with influenza alone and 6 (30%) with
influenza plus RSV co-infection. Five of the 20 children had neu-
rological problems, 4 with first-time seizures associated with the
admission illness, and 1 child had hydrocephalus. Three children
with confirmed influenza had high-cost hospitalizations for which
influenza did not clearly account for the majority of the costs.
The primary causes of these 3 hospitalizations included supraven-
tricular tachycardia with respiratory distress, Epstein-Barr Virus
infection with fever and dehydration, and cervical adenitis requir-
ing incision and drainage.
After controlling for age, race, insurance type, and gender, only
ICU use was significantly associated with high cost. Prematurity,
RSV co-infection, high-risk status, and pneumonia were not sig-
nificantly associated with high cost. In multivariable analyses of
factors predicting ICU stay after adjusting for race, age, gender and
insurance status, only high-risk status was significantly associated
with ICU stay. RSV co-infection, prematurity, and pneumonia were
not significantly associated with ICU stay (data not shown).
3.4. Projected national costs of influenza-related hospitalizations
and ED visits
(0.4–1.5 per 1000 [CI: 0.2–1.9, Table 4])  and the mean costs per
hospitalization from this study ($5402, Table 2), and extrapolating
to the US population of children younger than 5 years of age ,
we estimate annually between 8059 and 30,219 (CI: 4029–38,278)
influenza-related hospitalizations in the US accounting for $43.53
and $163.25 million (CI: $21.77–$206.78 million) in direct medical
ED rates varied from 6 to 27 per 1000 children (CI: 4–33). Using
the overall mean cost of an ED visit, as reported in Table 2 ($512),
and extrapolating to the US population of children younger than 5
years of age , we estimate between 120,878 and 543,951 (CI:
80,585–664,829) influenza-related ED visits accounting for $61.89
to $278.50 million (CI: $41.26–$340.39 million) in direct medical
costs occur annually.
This is the first study of the cost burden of influenza on children
that utilized population-based surveillance in different geograph-
ical sites over multiple influenza seasons, and involved costs for
both hospitalized children and children cared for in the ED [6,8,9].
children, and $512 and $409, respectively for children cared for in
the ED over 3 influenza seasons.
Our average cost of hospitalization ($5402) was consistent, but
slightly lower than costs reported in one prior study ($6124) ,
and considerably lower than costs reported in two other pediatric
studies in Philadelphia ($13,159)  and Chicago ($13,446) .
These latter two studies included older children with a higher pro-
portion of high-risk children and were conducted at major regional
tertiary care centers.
Although most attention has understandably focused on hospi-
talizations due to influenza, our findings highlight the important
contribution of ED visit rates and costs to the overall annual eco-
nomic burden of influenza in the US. National cost burden of
influenza-related hospitalizations and ED visits were estimated at
$43 to $163 million and $62 to $289 million, respectively. Thus,
their much greater frequency results in a considerable population-
wide burden that is comparable to the cost of hospitalizations due
This study is also the first that retrospectively examined charts
of high-cost children to determine whether hospitalizations or ED
visits were clinically attributable to influenza and its complica-
tions or to other conditions unrelated to the influenza infection.
Our findings that resource utilization rates and costs for 85% of the
children with the high-cost care were due to influenza infection
or complications directly related to influenza or co-infections of
influenza and RSV highlight the unequivocal disease effect on this
population. Children in this group often had complications of their
underlying conditions, which were triggered by influenza. These
findings, along with the fact that this study was population-based,
provide greater confidence in our extrapolations of the cost burden
of influenza nationwide.
gies to increase vaccination rates, as well as targeted preventive
strategies toward selected at-risk children. With respect to the
first point, our data show that ED visits and low-risk hospitaliza-
tions contribute substantially to the overall costs, as the number of
ED visits is far larger than the number of hospitalizations, and far
more hospitalizations occur among low-risk children than among
high-risk children. Vaccination rates were low in this population
(fewer than 30% of children aged 6–23 months and fewer than 20%
G. Fairbrother et al. / Vaccine 28 (2010) 4913–4919
of children 24–59 months were fully vaccinated in the 2006–07
season) . Our findings suggest that the most important strat-
egy for containing costs is to vaccinate all children, supporting the
recent recommendations for routine influenza vaccination of chil-
dren up through 18 years of age . Furthermore, this research
demonstrated that vaccinating children <6 months of age, if a vac-
cine could be licensed in this age group, could have a substantial
impact on hospitalization costs.
The need to vaccinate pregnant women and household and
other contacts of young children is emphasized by 45% of the bur-
den of influenza costs being from infants under 6 months of age. As
of Pediatrics (AAP) and the Advisory Committee on Immunization
Practices (ACIP) recommend vaccinating women who will be preg-
nant during the influenza season, and also all household contacts
and out-of home caregivers of children <5 years old, as well as all
children with chronic medical conditions . However, current
vaccination rates of pregnant women and of children are poor (13%
and <40%, respectively in the 2006–07 season) , indicating the
need for additional efforts and strategies to raise these rates.
The increased proportion of influenza plus RSV co-infection
cases among those with severe illness raises questions about the
risk of more severe disease among co-infected children and risk for
co-infection. However, the relatively small number of such cases
precluded additional analyses. Other studies should be considered
to better explore issues related to influenza and RSV co-infection.
surveillance across 3 seasons and 3 separate geographic settings
(188 hospitalized patients and 202 patients seen in the ED) and
included only children <5 years of age. Furthermore, since the 3
surveillance sites were in the Northeast, South, and Midwest, our
findings may not be representative of other areas within in the US.
mate total medical costs by approximately 6% to 14% . The lack
indicate little flexibility of hospitals to depart from fees in service
contracts with physicians for a variety of reasons including cost-
shifting, uncompensated care, competition for physician services
or other pecuniary, institutional, or idiosyncratic issues implicit
in physician service contracts as analyzed elsewhere [20,30–32].
However, from a payer’s perspective we believe that our base case
total medical cost estimates are close approximations to the true
Costs associated with influenza hospitalizations and ED visits
the US. Hospitalizations and ED visits by healthy infants and young
children account for the largest share of cost, because of their large
numbers. The single best way to prevent influenza and its associ-
ated costs is to vaccinate all children, as well as the household and
other contacts of those children too young to be vaccinated.
Author contributions: Dr Fairbrother had full access to all of the
data in the study and takes responsibility for the integrity of the
data and the accuracy of the data analysis.
Study concept and design: Fairbrother, Cassedy, Staat, Ortega-
Acquisition of data: Cassedy, Henderson, Ambrose, Kent.
Analysis and interpretation of data: Fairbrother, Cassedy, Staat,
Drafting of the manuscript: Cassedy, Fairbrother, Staat.
Critical revision of the manuscript for important intellectual con-
Molilnari, Poehling, Weinberg, Griffin, Molinari, Bridges, Donauer,
Statistical analysis: Cassedy.
Obtained funding: Staat.
Study supervision: Fairbrother, Staat, Ortega-Sanchez.
Financial Disclosures: The following authors have made disclo-
sure: Marie Griffin has Marie R Griffin, MD, MPH has investigator
initiated grant funding from MedImmune. Caroline Hall, MD
has consulted for MedImmune. Mary Allen Staat, MD, MPH, has
rotavirus research funding from Merck and Company and from
Conflicts of interest: The other authors declare that they have no
financial disclosures or conflicts of interest.
Funding/Support: CDC provided funding through cooperative
agreements with the 3 sites.
Role of the Sponsor: CDC provided data management support for
the NVSN surveillance data. The study had CDC co-author(s) and
CDC staff reviewed.
Clinical Centers: None.
We thank all the practices who participated in this study. In
addition, we thank the following members of the NVSN:
Nashville: Carol Ann Clay, RN, Erin Keckley, RN, Diane Kent, RN,
Nayleen Whitehead, Yuwei Zhu, MD, MS.
Rochester: Christina Albertin, MPH, Geraldine Lofthus, PhD, Ken
Cincinnati: Vanessa Florian, Michol Holloway, MPH, Linda Jami-
son, RN, Meredith E. Tabangin, MPH.
 Molinari NA, Ortega-Sanchez IR, Messonnier ML, Thompson WW, Wortley PM,
disease burden and costs. Vaccine 2007;25(27):5086–96.
 Neuzil KM, Mellen BG, Wright PF, Mitchel Jr EF, Griffin MR. The effect of
influenza on hospitalizations, outpatient visits, and courses of antibiotics in
children. N Engl J Med 2000;342(4):225–31.
 Neuzil KM, Zhu Y, Griffin MR, Edwards KM, Thompson JM, Tollefson SJ, et al.
Burden of interpandemic influenza in children younger than 5 years: a 25-year
prospective study. J Infect Dis 2002;185(2):147–52.
 Poehling KA, Edwards KM, Weinberg GA, Szilagyi P, Staat MA, Iwane MK, et
al. The underrecognized burden of influenza in young children. N Engl J Med
 Thompson WW, Shay DK, Weintraub E, Brammer L, Bridges CB, Cox
NJ, et al. Influenza-associated hospitalizations in the United States. JAMA
 Ampofo K, Gesteland PH, Bender J, Mills M, Daly J, Samore M, et al.
Epidemiology, complications, and cost of hospitalization in children with
laboratory-confirmed influenza infection. Pediatrics 2006;118(6):2409–17.
 Hall JL, Katz BZ. Cost of influenza hospitalization at a tertiary care children’s
hospital and its impact on the cost-benefit analysis of the recommendation
for universal influenza immunization in children age 6 to 23 months. J Pediatr
 Keren R, Zaoutis TE, Saddlemire S, Luan XQ, Coffin SE. Direct medi-
calcost of influenza-relatedhospitalizations
 Cox FM, Cobb MM, Chua WQ, McLaughlin TP, Okamoto LJ. Cost of treating
influenza in emergency department and hospital settings. Am J Manag Care
 Ireys HT, Anderson G, Shapffer TJ, Neff JM. Expenditures for care of children
with chronic illnesses enrolled in the Washington State Medicaid program,
fiscal year 1993. Pediatrics 1997;100:197–204.
 Liptak GS, Shone LP, Auinger P, Dick AW, Ryan SA, Szilagyi PG. Short-term
persistence of high health care costs in a nationally representative sample of
children. Pediatrics 2006;118(October (4)):e1001–9.
 McCormick MC, Weinick R, Elixhauser A, Stagnitti MN, Thompson J, Simpson L.
Annual report on access to and utilization of health care for children and youth
in the United States: 2000. Ambul Pediatr 2001;1:3–15.
 Eisenberg KW, Szilagyi PG, Fairbrother G, Griffin MR, Staat M, Shone LP, et al.
Vaccine effectiveness against laboratory-confirmed influenza in children 6 to
59 months of age during the 2003–2004 and 2004–2005 influenza seasons.
G. Fairbrother et al. / Vaccine 28 (2010) 4913–4919 Download full-text
 Griffin MR, Walker FJ, Iwane MK, Weinberg GA, Staat MA, Erdman DD. Epi-
demiology of respiratory infections in young children: insights from the new
vaccine surveillance network. Pediatr Infect Dis J 2004;23(11 Suppl.):S188–92.
 Hall CB, Weinberg GA, Iwane MK, Blumkin AK, Edwards KM, Staat MA, et al.
The burden of respiratory syncytial virus infection in young children. N Engl J
 Iwane MK, Edwards KM, Szilagyi PG, Walker FJ, Griffin MR, Weinberg GA, et
al. Population-based surveillance for hospitalizations associated with respira-
tory syncytial virus, influenza virus, and parainfluenza viruses among young
children. Pediatrics 2004;113(June (6)):1758–64.
 Szilagyi PG, Fairbrother G, Griffin MR, Hornung RW, Donauer S, Morrow A,
et al. Influenza vaccine effectiveness among children 6 to 59 months of age
during 2 influenza seasons: a case-cohort study. Arch Pediatr Adolesc Med
control of influenza. Recommendations of the Advisory Committee on Immu-
 Luce BR, Manning WG, Siegel JE, Lipscomb J. Estimating costs in cost-
effectiveness analysis. In: Gold MR, Siegel JE, Russell LB, Weinstein MC, editors.
Cost-effectiveness in health and medicine. New York: Oxford University Press;
1996. p. 200–3.
 Dowless RM. The health care cost-shifting debate: could both sides be right? J
Health Care Finance 2007;34(Fall (1)):64–71.
 Wynn BO, Scott MM. Evaluation of Alternative Methods to Establish DRG Rela-
Available from: http://www.rand.org/pubs/working papers/WR560/.
 Bourgeois FT, Valim C, Wei JC, McAdam AJ, Mandl KD. Influenza and other
respiratory virus-related emergency department visits among young children.
 Izurieta HS, Thompson WW, Kramarz P, Shay DK, Davis RL, DeStefano F, et al.
Influenza and the rates of hospitalization for respiratory disease among infants
and young children. N Engl J Med 2000;342(4):232–9.
 O’Brien MA, Uyeki TM, Shay DK, Thompson WW, Kleinman K, McAdam A, et
al. Incidence of outpatient visits and hospitalizations related to influenza in
infants and young children. Pediatrics 2004;113(3 Pt 1):585–93.
 U.S. Census Bureau PD. Annual Estimates of the Population by Sex and Five-
Year Age Groups for the United States: April 1, 2000 to July 1, 2007. U.S. Census
Bureau, Population Division.
 Influenza vaccination coverage among children aged 6–59 months—six
immunization information system sentinel sites, United States, 2006–07
influenza season. MMWR Morb Mortal Wkly Rep 2007;56(September 21 (37)):
 Centers for Disease Control and Prevention (CDC). Prevention and Control of
Influenza: Recommendations of the Advisory Committee on Immunization
Practices (ACIP), 2008. Morbidity and Mortality Weekly Report: Coordinat-
ing Center for Health Information and Service, Centers for Disease Control and
Prevention (CDC), U.S. Department of Health and Human Services; 2008.
 Zaman K, Roy E, Arifeen SE, Rahman M, Raqib R, Wilson E, et al. Effective-
ness of maternal influenza immunization in mothers and infants. N Engl J Med
 (CDC) CfDCaP. Influenza Vaccination Coverage Levels; 2009. Available from:
 Morrisey MA. Hospital pricing: cost shifting and competition. EBRI Issue Brief
 Gruber J, Rodriguez D. How much uncompensated care do doctors provide? J
Health Econ 2007;26(December 1 (6)):1151–69.
 Finkler SA. The distinction between cost and charges. Ann Intern Med