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OpenAthens Shibboleth
Sep 2011

Patient Volume and Quality of Care for Young Children Hospitalized With Acute Gastroenteritis

Author Affiliations

Author Affiliations: Department of Pediatrics (Drs McLeod and Keren) and Center for Pediatric Clinical Effectiveness (Drs Dai and Keren), Children's Hospital of Philadelphia, and Department for Biostatistics and Epidemiology (Drs French and Localio) and Leonard Davis Institute of Health Economics (Dr French), University of Pennsylvania, Philadelphia.

Arch Pediatr Adolesc Med. 2011;165(9):857-863. doi:10.1001/archpediatrics.2011.132

Objective To explore the relationship between the volume of children admitted to the hospital with acute gastroenteritis and adherence to recommended quality indicators.

Design Retrospective cohort study.

Setting Premier Perspective clinical and financial information systems database (Premier Inc, Charlotte, North Carolina).

Participants A total of 12 604 otherwise healthy children aged 3 months to 10 years hospitalized between January 1, 2007, and December 31, 2009, at 280 US hospitals with International Classification of Diseases, Ninth Revision diagnosis codes indicating acute gastroenteritis.

Main Exposure Volume of hospital admissions per year of children with acute gastroenteritis.

Main Outcome Measures Quality indicators for overuse and misuse of care in the management of acute gastroenteritis based on nationally published guidelines. These include blood testing, stool studies, use of antibiotics, and use of nonrecommended antiemetic or antidiarrheal medications (hereafter referred to as nonrecommended medications).

Results Selected blood, stool, and rotavirus tests (overuse indicators) were performed in 85%, 46%, and 56% of children, respectively. Six percent of children received nonrecommended medications, and 26% received antibiotics (misuse indicators). Higher volumes of hospital admission for acute gastroenteritis were associated with less use of blood tests (odds ratio [OR], 0.67 [95% confidence interval {CI}, 0.50-0.89]), nonrecommended medications (OR, 0.84 [95% CI, 0.76-0.93]), and antibiotics (OR, 0.93 [95% CI, 0.86-0.99]). Children admitted to hospitals in the 25th vs 75th percentile of patient volume had a 10%, 30%, and 10% increased chance of having blood tests, nonrecommended medications, and antibiotics ordered, respectively.

Conclusions In a nationally representative sample of hospitals that care for children with acute gastroenteritis, higher patient volumes were associated with greater adherence to established quality indicators. Further investigation is needed to identify the hospital characteristics driving the volume-quality relationship for this common pediatric condition.

There is substantial variation in the processes and outcomes of care for hospitalized children.1,2 Although much of this variation can be attributed to the paucity of uniform standards and evidence-based guidelines for the management of pediatric diseases in the hospital, variation in the management of common conditions for which best practices exist remains high.35 For acute gastroenteritis in particular (a common condition with established guidelines shown to reduce costs, length of hospital stay, and duration of illness),68 more than 30% of children at a sample of US major children's hospitals received care inconsistent with current guidelines.4 The reasons for this low adherence to best practices are unknown.

Patient volume (ie, the number of patients admitted to the hospital) is one known determinant of variation in quality of care.9 For conditions that require intensive care or complex surgical procedures and for various common adult conditions, higher patient volumes have been associated with lower mortality.913 In some cases, greater adherence to evidence-based practices explained some, but not all, of the volume effect.1416 As for any learned skill, the accumulation of experience by individual providers likely accounts for some volume-related differences in quality.17 However, low-volume providers sometimes achieve better outcomes in high-volume settings,18 indicating that the mechanism driving the volume-outcome relationship is more complex than the accumulation of disease experience, and that volume likely represents a proxy for organizational and structural attributes of a hospital that stimulate quality improvements and lead to better outcomes.19

For children hospitalized with common conditions, little is known about the complex relationship between volume and quality. Using a large representative sample of both children's and general US hospitals, we sought to characterize the relationship between patient volume and adherence to quality indicators in the care of children hospitalized with acute gastroenteritis.


We conducted a retrospective cohort study using administrative data from the Premier Perspective database (Premier Inc, Charlotte, North Carolina). The internal review board of the Children's Hospital of Pennsylvania in Philadelphia approved the study protocol and waiver of consent.


Premier Perspective is the largest clinical and operational data warehouse in the nation and contains longitudinal inpatient and ambulatory data pertaining to all discharges from more than 600 hospitals representing approximately 20% of all discharges nationwide. Characteristics of the participating hospitals and their patient populations reflect the patient and hospital statistics reported in the American Hospital Association 2007 National Discharge Survey report.20 Each patient record in Premier Perspective includes a complete list of International Classification of Diseases, Ninth Revision (ICD-9) diagnosis and procedure codes, comprehensive line-item billing data, payer information, and patient demographics. All data undergo 95 separate quality assurance checks by Premier Inc before they are made available for research (


We restricted the study cohort to children 0 to 10 years of age who were discharged from an inpatient facility between January 1, 2007, and December 31, 2009, with at least 1 ICD-9 diagnosis code from the list of codes that the Centers for Disease Control and Prevention uses to identify children with acute gastroenteritis (eTable).21

To obtain a homogenous cohort of children with acute gastroenteritis, we excluded (1) children who had a discharge diagnosis on the index admission or who had previous admissions indicating the presence of a complex chronic condition,22 (2) children who had diagnosis or procedure codes not consistent with acute gastroenteritis, (3) children who received therapies used to manage acute conditions unrelated to acute gastroenteritis (eg, combinations of steroids and β-agonists or oxygen therapy), (4) children who were transferred in from an outside hospital, or (5) children who were younger than 90 days old at admission (eFigure). A detailed list of the exclusion criteria and corresponding codes (when applicable) can be found in the eTable.


We identified 5 quality indicators pertaining to the use of medications or tests that are explicitly not recommended in guidelines for the management of routine acute gastroenteritis published by the Centers for Disease Control and Prevention and the American Academy of Pediatrics.2325 Quality indicators were then grouped into categories of either misuse or overuse of care. Misuse indicators were defined as (1) use of nonrecommended antiemetic or antidiarrheal medications (hereafter referred to as nonrecommended medications) known to carry risks of major adverse effects in young children (promethazine hydrochloride, prochlorperazine edisylate, metoclopramide hydrochloride, hyoscyamine sulfate, and loperamide hydrochloride) and (2) use of antibiotics. Overuse indicators were defined as (1) acquiring a complete blood count or performing a blood culture, (2) performing stool cultures or parasite screens, and (3) testing for rotavirus.


Volume was measured in terms of both the number of children admitted to the hospital with acute gastroenteritis, in particular (ie, patient volume), and the annual number of children admitted to the hospital, in general (ie, total patient volume). For each hospital, we calculated the number of children admitted to the hospital with acute gastroenteritis per year (after exclusion of children with complex chronic conditions and other acute illnesses) and the total number of children admitted to the hospital per year (all children aged 1-10 years) by dividing the count of each type of admission over the study period by the number of years that the hospital provided data (89% of hospitals provided data for all 3 years). We excluded hospitals with less than 1 admission for acute gastroenteritis per year.


Hospital-level covariates included location (urban or rural), region (North, South, East, or West), American Hospital Association–defined teaching status (teaching or nonteaching), case mix, and payer mix. Case mix represented the mean all patient refined–diagnosis related group (APR-DRG) severity score (from 1 for minor case to 4 for severe case) across all pediatric admissions,26 and payer mix represented the percentage of all pediatric admissions with government-funded insurance (Medicaid, Medicare, charity care, and uninsured or self-pay). Patient-level covariates included sex, race, age in years, source of admission, attending physician specialty, quarter of the year of admission, APR-DRG severity score, and primary insurance payer (government or uninsured vs private insurer).


Bivariable analyses were first performed to compare the distribution of patient- and hospital-level covariates across both continuous volume and volume categories (defined by terciles of patient volume). Unadjusted associations of covariates with each outcome were then calculated using multilevel regression methods to account for clustering of patients within hospitals.

To determine the population-averaged effect of patient volume on adherence to quality indicators, we used generalized estimating equation–supported logistic regression designed for analysis of complex survey data.27,28 When applied to multilevel data, these methods require the use of probability sampling for variance estimation and provide unbiased marginal estimates when the true correlation structure is unknown.29 Compared with hospital-level effects, physician-level effects contributed little to the outcome heterogeneity. Thus, only nesting of patients within hospitals was accounted for in the reported models. Mixed-effects logistic regression, accounting for various levels of clustering, produced similar estimates and standard errors in repeated analyses.

Patient volume was treated as a continuous variable, rather than a categorical variable, to avoid the potential bias introduced by the high degree of variability of outcomes within volume categories.30 A log base 2 transformation was used to form contrasts in the odds of misuse or overuse between 2 populations whose patient volume differed by a multiplicative factor of 2. To reduce potential confounding by hospital-level characteristics when estimating associations between patient-level covariates and outcomes, we decomposed the severity and payer variables into a hospital term that represented the average value within each hospital and a patient term that represented the deviation of each patient's characteristic from the hospital average.31

We fit separate models to estimate the effect of each patient volume measure (number of children admitted to the hospital with acute gastroenteritis and total number of children admitted to the hospital) on each quality indicator. Adjusted odds ratios (ORs) were estimated by including all relevant patient- and hospital-level covariates as detailed in the “Patient- and Hospital-Level Covariates” and “Statistical Analyses” subsections of the “Methods” section. We used a combination of manual selection and backward elimination to select covariates for inclusion in the final models. Covariates were retained in the model (1) if they were significantly associated with the outcome (P < .01), (2) if the Hosmer-Lemeshow goodness-of-fit test statistic was significant (P < .05), (3) if the addition or removal of the covariate changed the estimated patient volume coefficient by more than 10%, or (4) for face validity. Hospital case mix was excluded from the models owing to its collinearity with patient volume. Other variables highly associated with volume (location, region, and teaching status) were forced into the final models, with subsequent subgroup analyses performed. Marginal probabilities of each outcome at the 25th and 75th percentiles of patients with acute gastroenteritis were estimated from adjusted models.32 All data management and statistical analyses were performed using Stata version 11.0 (StataCorp, College Station, Texas) and SAS version 9.2 (SAS Institute Inc, Cary, North Carolina).


A projected sample size of 10 000 children was estimated from preliminary review of the data. Assuming that between 5% and 80% of children may have had one of the tests or may have used one of the medications associated with their admission, we found that the detectable differences for a power of 0.9 at an alpha level of .05 would be 1% to 3%, accounting for regression of multiple covariates on the exposure of interest with an estimated R2 of 0.5.


A total of 12 604 children aged 3 months to 10 years admitted to 280 US hospitals were included in our study (eFigure). The sampled hospitals were similar to the hospitals in the complete Premier Perspective database in terms of size, region or location, and most other demographic characteristics (Table 1).20 The overall number of children admitted to the hospital with acute gastroenteritis ranged from 1 to 174 children per year, with median patient volumes within small, medium, and large categories of hospitals (defined by lowest to highest terciles of volume) of 7, 13, and 30 patients per year, respectively. Patient volumes based on age were highly correlated with hospital bed size and total admissions.

Table 1. Hospital Characteristics Overall and Across Volume Categories of Children Admitted per Year With Acute Gastroenteritisa
Table 1. Hospital Characteristics Overall and Across Volume Categories of Children Admitted per Year With Acute Gastroenteritisa
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Just under half (46%) of the hospitals were in Southern urban locations. Large hospitals, in addition to admitting patients with the highest severity of illness, were predominantly Southern, urban, and teaching hospitals. Payer mix (percentage with government insurance) did not vary by hospital size.


Eighty percent of children in the study sample were between the ages of 3 months and 3 years (Table 2). The majority of children were admitted from the emergency department (58%), were cared for in the hospital by pediatricians (79%), had a length of hospital stay between 1 and 3 days (92%), and were rated as having a minor severity of illness at hospital discharge (78%). Nearly all patient characteristics were well balanced across volume categories.

Table 2. Patient Characteristics Overall and Across Volume Categories of Children Admitted per Year With Acute Gastroenteritis
Table 2. Patient Characteristics Overall and Across Volume Categories of Children Admitted per Year With Acute Gastroenteritis
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Use of nonrecommended medications was generally low (6% of children) and varied by location and region, ranging from 1.5% of children in Northeastern urban hospitals to 16% of children in Southern rural hospitals. Twenty-six percent of the children received antibiotics. Use was higher if bacterial gastroenteritis as opposed to viral or nonspecific gastroenteritis was diagnosed (63% vs 23% of children) and ranged from 14% of children in Northeastern urban hospitals to 37% of children in Southern rural hospitals.

After adjustment for patient- and hospital-level covariates, higher volumes of patients admitted to hospitals with acute gastroenteritis were associated with less frequent use of nonrecommended medications (OR, 0.84 [95% confidence interval {CI}, 0.76-0.93]) and antibiotics (OR, 0.93 [95% CI, 0.86-0.99]). Similar correlations were found between higher total patient volumes and frequency of nonrecommended medication and antibiotic use. Excluding children with bacterial gastroenteritis did not change the direction or significance of the associations, and adjusting for physician volume had no effect on the estimates.

Marginal probabilities estimated from adjusted analyses indicated that children with gastroenteritis had a 30% increased chance of receiving nonrecommended medications and a 10% increased chance of receiving antibiotics if they were admitted to a hospital at the 25th percentile of patient volume compared with admission to a hospital at the 75th percentile of patient volume (Figure 1).

Image not available

Figure 1. Percentage of children who received nonrecommended care after admission to hospitals in the 25th (dark gray bars) and 75th (light gray bars) percentiles of patient volume. A, Indicators of misuse of care were use of antiemetic or antidiarrheal medications (ie, nonrecommended medications) and antibiotics. B, Indicators of overuse of care were acquiring a complete blood count or performing a blood culture, performing stool cultures or parasite screens, and testing for rotavirus. Predicted probabilities and 95% confidence intervals (error bars) were obtained from the fully adjusted regression models.


Blood tests were performed for 80% of children, ranging from 76% of children in Northeast urban hospitals to 94% of children in Southern rural facilities. Being diagnosed with bacterial gastroenteritis did not significantly alter these percentages. Stool testing and rotavirus testing occurred in 46% and 56% of children, respectively, with less variation in testing across regions and locations.

In adjusted analyses, higher volumes of patients admitted to the hospital with acute gastroenteritis were associated with less frequent use of blood testing (OR, 0.67 [95% CI, 0.50-0.89]). The association was stronger for total patient volumes, and adjusting for physician volume did not affect the estimates. Odds ratios for the association of patient volume and total patient volume with stool testing were consistently less than 1, but these ORs did not achieve statistical significance in any model. Rotavirus testing increased in frequency with higher patient and total patient volumes but also failed to reach statistical significance in the adjusted models (patient volume: OR, 1.1 [95% CI, 0.99-1.3]).

Marginal probabilities estimated from adjusted analyses indicated that children with acute gastroenteritis had a 10% increased chance of having blood tests performed if they were admitted to a hospital at the 25th percentile of patient volume compared with admission to a hospital at the 75th percentile of patient volume (Figure 1). Adjusted ORs and CIs for the effects of patient and total patient volumes on outcomes are listed in Table 3. Figure 2 shows the unadjusted (lines) and adjusted (plotted points) fitted values describing the linear relationship between volume and each outcome. The x-axis is on a log base 2 scale to illustrate the correlation between each doubling of patient volume and adherence to the quality indicators.

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Figure 2. Change in percentage of children receiving nonrecommended care for every doubling of patient volume. Fitted values from unadjusted (lines with shaded 95% confidence intervals) and fully adjusted (points depicting mean fitted value within each decile of volume) regression models are shown. The P values evaluate whether the slope of the fully adjusted model is equal to 0.

Table 3. Adjusted Odds of Outcomes Across Average Annual Admissions for Acute Gastroenteritis and Average Annual Total Admissions of Patients 0 to 10 Years of Agea
Table 3. Adjusted Odds of Outcomes Across Average Annual Admissions for Acute Gastroenteritis and Average Annual Total Admissions of Patients 0 to 10 Years of Agea
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In a large nationally representative sample of US hospitals, we found that higher patient volumes were associated with greater adherence to accepted indicators of quality in the management of children with acute gastroenteritis. Although misuse and overuse of care were significantly associated with certain hospital characteristics (eg, location, region, and teaching affiliation), adjusting for these and other relevant patient- and hospital-level confounders did not alter the observed effect. Of the 12 604 children included in our study, 16% were admitted to hospitals that admit 20 or fewer children per week in total and 1 or fewer children per month with acute gastroenteritis.

Previous studies that demonstrated a volume-quality association in pediatric hospital care focused on highly specialized and relatively low volume hospital services such as intensive care and cardiac surgery, in which experience seemed most likely to make a difference in outcomes.10,11 However, our study shows that, even in the hospital care of much more common conditions like acute gastroenteritis, a similar volume-quality association exists and is unrelated to the volume of patients admitted by individual physicians. However, misuse and overuse of care among high-volume hospitals were still appreciably high for some outcomes. Furthermore, adherence to guidelines was not homogenous within volume categories; that is, adherence was lower than average for some larger hospitals and higher than average for some smaller hospitals. This suggests that the slope of the experiential learning curve that results in greater adherence to best practices may be modified by systems-level structural and organizational factors.17 Investment in organizational and structural change is likely influenced by the volume of pediatric admissions, more specifically, the volumes beyond which perceived benefits begin to outweigh costs. But evidence for the effectiveness of these systems-level changes cannot be ignored. Qualifications of frontline providers (hospitalists vs generalists) have been shown to be associated with improvements in certain outcome measures.33,34 Implementation of practice guidelines for conditions such as acute gastroenteritis can reduce misuse and overuse of care by disseminating best practices to providers of all levels of experience.35,36 And provider order entry systems with pediatric-specific decision support can reduce adverse events by alerting low-experience providers to medications contraindicated in children or providing guideline-based order sets as a starting point for clinical decision making.3739 More research is needed to identify other factors that improve quality and can be adopted by low-volume hospitals.40

Our study has a few potential limitations. First, variation in hospital coding practices may lead to misclassification of cases. To reduce this bias, we used all available patient data, such as medications, procedures, and unit assignments, to exclude children with conditions other than routine gastroenteritis. Second, administrative data lack clinical indicators of patient severity. To minimize confounding by severity and select children in whom these particular tests and medications would have a low likelihood of altering clinical decision making or outcomes, we restricted the study population, excluding children with chronic conditions, children who were admitted to the intensive care unit on the first day of hospitalization, and children with unrelated acute conditions such as meningitis.41 The resulting cohort of children had nearly uniform lengths of hospital stay, DRG codes, and APR-DRG severity scores. It is possible that, in some remaining cases, the care that was provided according to our definition of “nonrecommended” care may have been appropriate, but it is unlikely that the relationship described could be attributed entirely to this phenomenon.

Third, there is some debate about whether the use of practice guidelines is appropriate to evaluate quality of care. Although there are few validated guidelines for the management of common conditions in pediatrics, recommended care for acute gastroenteritis has been determined by extensive review of the available literature and consensus between experts from several organizations.25 Furthermore, there is empirical evidence that adherence to recommended care for children with acute gastroenteritis decreases costs, length of hospital stay, and duration of illness.4,68 We are aware that some hospitals may use rotavirus testing for infection control and surveillance purposes. This type of testing is unrelated to patient care, and when inappropriately billed to a patient's insurance provider, this type of testing also falls in the category of nonrecommended care for the individual.

Lastly, despite accounting for relevant patient- and hospital-level covariates, unmeasured confounders may have influenced our results. As mentioned earlier, volume is likely a surrogate, not the sole determinant, of quality, and more research is needed to identify the structural and organizational characteristics of hospitals that are associated with both volume and quality improvement.

In conclusion, using a nationally representative sample of hospitals that care for children with gastroenteritis,20 we found that higher patient volumes were associated with greater adherence to established guidelines. The effect was heterogeneous within volume categories and was unrelated to physician volume, indicating that higher quality was not solely due to experiential learning. To ensure high-quality hospital care for all children, more research is needed to identify structural and organizational characteristics that drive quality for common pediatric conditions, regardless of hospital size.

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Article Information

Correspondence: Lisa McLeod, MD, Department of Pediatrics, Children's Hospital of Philadelphia, 34th and Civic Center Boulevard, Center for Pediatric Clinical Effectiveness, North Ste 1550, Philadelphia, PA 19104 (

Accepted for Publication: April 5, 2011.

Author Contributions: Dr McLeod had full access to all 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: McLeod, French, Localio, and Keren. Acquisition of data: McLeod, Dai, and Keren. Analysis and interpretation of data: McLeod, French, Dai, Localio, and Keren. Drafting of the manuscript: McLeod, Localio, and Keren. Critical revision of the manuscript for important intellectual content: McLeod, French, Dai, Localio, and Keren. Statistical analysis: McLeod, French, Dai, and Localio. Obtained funding: McLeod and Keren. Study supervision: Localio and Keren.

Financial Disclosure: None reported.

Funding/Support: Dr McLeod was supported by a National Research Service Award institutional training grant for primary medical care (T32-HP010026). This project was supported by a Health Research Formula Grant from the Pennsylvania Department of Public Health Commonwealth Universal Research Enhancement Program (SAP 4100050891).

Role of the Sponsors: The funding sources had no role to play in the design and conduct of the study; the collection, management, analysis, and interpretation of the data; or in the preparation, review, or approval of the manuscript.

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