infection control and hospital epidemiologyjune 2009, vol. 30, no. 6
Association Between Physician Caseload and Patient Outcome
for Sepsis Treatment
Chao-Hung Chen, MD, MPH; Yi-Hua Chen, PhD; Hsiu-Chen Lin, MD; Herng-Ching Lin, PhD
as lower in-hospital mortality rates, for patients with sepsis.
The purpose of this study was to investigate whether physicians with larger sepsis caseloads provide better outcomes, defined
design. Retrospective cross-sectional study.
patients hospitalized with a principal diagnosis of septicemia were selected and assigned to 1 of 4 caseload groups on the basis of their
treating physician’s sepsis caseload during the 3 years reflected in the pooled data (low caseload, less than 39 cases; medium caseload, 39–
88 cases; high caseload, 89–176 cases; and very high caseload, more than 176 cases). Generalized estimating equation models were used
This study used pooled data from the 2002–2004 Taiwan National Health Insurance Research Database. A total of 48,336
hospital mortality by 49% (95% confidence interval [CI], 0.41–0.67;
0.92; ), respectively, compared with the odds for patients treated by low-caseload physicians.ThesefindingspersistedafterpartitioningP ! .001
out systematic physician-specific and hospital-specific variation and isolating the effects of most hospital, physician, and patientconfounders.
Receipt of treatment from physicians in the very high, high, and medium caseload groups decreased patients’ odds of in-
P ! .001
), 40% (95% CI, 0.53–0.68; ), and 18% (95% CI, 0.73–
P ! .001
did patients treated by physicians in the other caseload groups, and the difference was statistically significant. This result supports the
“practice makes perfect” hypothesis.
Patients treated by physicians who had a larger sepsis caseload had a substantially lower in-hospital mortality rate than
Infect Control Hosp Epidemiol 2009; 30:556-562
From the Department of Thoracic Surgery, Mackay Memorial Hospital (C.-H.C.), the Mackay Medicine, Nursing, and Management College (C.-H.C.),
the Schools of Public Health (Y.-H.C.) and Healthcare Administration (H.-Ching Lin), Taipei Medical University, and the Department of Pediatric Infection,
Taipei Medical University Hospital, Taiwan (H.-Chen Lin)
Received September 7, 2008; accepted January 16, 2009; electronically published May 5, 2009.
? 2009 by The Society for Healthcare Epidemiology of America. All rights reserved. 0899-823X/2009/3006-0008$15.00. DOI: 10.1086/597509
Sepsis is a common and devastating syndrome that represents
a major cause of morbidity and mortality for hospitalized
patients.1An 8.7% annual increase in the incidence of sepsis
between 1979 and 2000 has been reported.2In addition, death
rates range from 15% to 20% for sepsis, from 25% to 30%
for severe sepsis, and from 40% to 70% for septic shock.3
Because of the high incidence, high mortality rate, and con-
sequent healthcare burden associated with sepsis, clinicians
and healthcare administrators frequently receive information
about sepsis that emphasizes early detection and appropriate
interventions to prevent deterioration of organ function.
Death that results from sepsis-induced organ failure is con-
sidered to be the consequence of an excessive or uncontrolled
host response to infection.4Because hospitals generally offer
the equipment needed to diagnose and treat sepsis, most of
the associated in-hospital mortality reflects the skills and clin-
ical experience of the attending physicians and the support
team.5Sepsis is an inherently complex disease that may be
treated by physicians with various levels of clinical experience,
and physician experience or caseload may play an important
role in treatment outcomes.
Numerous studies have reported an inverse association be-
tween caseload and the rate of adverse outcomes, as a result
of an increased awareness of accountability and elevated con-
cern for quality of care and patient safety among high-case-
load physicians.6,7In a review of more than 100 published
papers on hospital volume and outcome associations, 78%
concerned physician caseload and outcomes for major sur-
gical procedures,8,9and similar results were found for non-
surgical conditions requiring hospitalization, such as myo-
cardial infarction and receipt of intensive care.10,11Despite the
substantial body of literature, to our knowledge there have
been no studies to date that examined the effects of physician
caseload on outcomes for patients with sepsis.
Thus, the purpose of this nationwide, population-based
study was to investigate whether physicians with larger
caseload and outcomes for sepsis treatment557
pitalized for Treatment of Septicemia, According to Patient Char-
acteristics and Comorbidities: Taiwan, 2002–2004
Distribution of In-Hospital Mortality for Patients Hos-
In-hospital mortality, no.
(%) of patients
(n p 5,628)
(n p 42,708)
Congestive heart failure
Pulmonary circulation disorder
Peripheral vascular disorder
Chronic pulmonary disease
In-hospital mortality, no.
(%) of patients
(n p 5,628)
(n p 42,708)
Peptic ulcer disease, excluding
Solid tumor without metastasis
Fluid and electrolyte disorder
Blood loss anemia
5 (3.7) 129 (96.3)
42,579 (88.3) 5,623 (11.7)
1 (0.9) 105 (99.1)
42,603 (88.3)5,627 (11.8)
6 (37.5)10 (62.5)
42,698 (88.4) 5,622 (11.6)
7 (5.7)115 (94.3)
42,593 (88.3)5,621 (11.7)
9 (4.5)192 (95.5)
42,516 (88.3)5,619 (11.7)
mortality rate was 11.6%.
The total number of patients was 48,336, and the overall in-hospital
caseloads provide better outcomes for patients with sepsis.
The in-hospital mortality rate was used to assess treatment
This study used pooled data from the 2002–2004 National
Health Insurance Research Database (NHIRD) published by
558infection control and hospital epidemiologyjune 2009, vol. 30, no. 6
the Taiwan National Health Research Institute. The NHIRD
includes monthly claims summaries that consist of inpatient
claims, details of inpatient orders, a registry of medical fa-
cilities that have contracted with the National Health Insur-
ance (NHI) program, and a registry of board-certified spe-
cialists for every inpatient admission of a NHI beneficiary.
Taiwan’s NHI provides universal coverage to all citizens—
more than 21 million people (approximately 97% of Taiwan’s
population). It is a single plan thatprovidesgenerousbenefits,
low copayments, and free choice in a widely dispersed net-
work of healthcare providers. The NHIRD provides a unique
opportunity to explore the relationship between physician
caseload and treatment outcomes for sepsis. Because the
NHIRD consists of deidentified secondary data released to
the public for research purposes, this study was exempt from
full review by the institutional review board.
We selected all records for all patients who were hospitalized
with a principal diagnosis of septicemia (International Clas-
sification of Diseases, 9th Revision, Clinical Modification, code
038) ( ). We included only patients with aprincipaln p 63,169
diagnosis of septicemia to assure that all individuals selected
were admitted for treatment of septicemia, rather than other
disorders. We limited the study sample to the adult popu-
lation, excluding patients under 18 years of age (
We also excluded patients who were discharged against med-
ical advice or transferred to another hospital and patients
who had been transferred in from another hospital (n p
). We limited our study sample to first-time admissions,2,678
if a patient had been admitted more than once during the
period covered by the data (n p 7,892
timately, a total of 48,336 patients were included in this study.
).n p 4,263
cases excluded). Ul-
Physicians’ Septicemia Caseloads
Unique physician identifiers are available in the NHIRD for
each medical claim submitted, which enabled us to identify
when the same physician admitted 1 or more patients for
septicemia treatment during the study period. All physicians
identified as treating patients for septicemia were sorted in
ascending order of caseload, and caseload cutoff points were
determined so as to classify the sampled patients into4groups
of approximately equal size, in accordance with standard
practice.10,12,13The sample of 48,336 patients was thus divided
into 4 caseload groups on the basis of their treating physi-
cian’s sepsis caseload during the 3 years reflectedinthepooled
data. The caseload groups were as follows: fewer than39cases,
39–88 cases, 89–176 cases, and more than 176 cases (hereafter
referred to as the “low caseload,” “medium caseload,” “high
caseload,” and “very high caseload” groups, respectively).
We used SAS, version 9.1 (SAS Institute), for statistical anal-
ysis. The key independent variable of interest was physician
caseload, and the key dependent variable was in-hospital
death, for which ”patient” was the unit of analysis. In-hospital
death was treated as a dichotomous variable (yes or no) and
was defined as the death of a patient at any time after ad-
mission if the patient had not left the hospital.
Global x2analyses were conducted to examine the rela-
tionship between variables of interest and the unadjusted rate
of in-hospital patient deaths. We employed a generalized es-
timating equation model to account for any clustering of the
sampled patients with respect to particular hospitals and/or
In the modeling, we adjusted for physicians’ sex, age (di-
vided into the following 3 categories: younger than 41 years,
41–50 years old, and older than 50 years), and specialty (pre-
sented as infection, internal medicine, surgery, or other); the
hospital’s accreditation level; and patients’ age, sex, and co-
morbidities. The hospital accreditation level variable, which
was used as a proxy for both hospital size and clinical service
capabilities, classified each hospital as a medical center (with
a minimum of 500 beds), a regional hospital (minimum 250
beds), or a district hospital (minimum 20 beds). We adjusted
for patients’ comorbidities by using the Elixhauser Comor-
bidity Index.15This comorbidity index has been widely used
for risk adjustment in administrative data sets,16,17and it uses
30 binary comorbidity measures (ie, 1 indicates the comor-
bidity is present, and 0 indicates that it is absent) to account
for inpatient morbidity and mortality rates. On the basis of
available data and a literature review, we initially inserted all
potential variables in the model. Then, we used the quasi-
likelihood under the independence model criterion to select
an appropriate model, withthesmallestcriterionvaluechosen
as the best model.18
Finally, to detect a critical caseload level at which the haz-
ardous effects of low caseload vanished, we used model results
to ascertain the critical caseload that would divide the cohort
into 2 significantly different groups. A 2-sided P value of .05
Table 1 shows the distribution of in-hospital mortality after
treatment of septicemia, according to patient sex, age, and
comorbidities. Of 48,336 patients admitted during the 3 years
for which data were studied, 5,628 (11.6%) were discharged
at death. Global x2analyses showed that there were statisti-
cally significant differences in the in-hospital mortality rate
with respect to sex (), age (
P ! .001
(congestive heart failure [
P ! .001
], peripheral vascular disorders [
[ ], paralysis [ ], coagulopathy [
P ! .001P ! .001
rological disorders [P p .032
[ ], complicated diabetes [P ! .001
[ ], renal failure [P p .018P ! .001
peptic ulcer , solid tumors without metastasisP ! .001
, rheumatoid arthritis [P ! .001
), and comorbidity
P ! .001
], valvular disease [
P ! .001
P ! .001
], uncomplicated diabetes
P ! .001
], liver disease [
],P ! .001
], fluid and elec-P p .028
caseload and outcomes for sepsis treatment559
table 2. Physician and Patient Data, According to Physicians’ Septicemia Caseload Group: Taiwan, 2002–2004
Low, !39 cases Medium, 39–88 cases High, 89–176 casesVery high, 1176 cases
In-hospital mortality rate, %
Sepsis caseload, mean ? SD
Mean ? SD
Mean ? SD
3,556 818378 136
13.7 ? 10.058.0 ? 14.0 120 ? 24.4276 ? 99.7
43.2 ? 7.9
42.1 ? 7.0
42.2 ? 6.9
43.1 ? 7.1
68.8 ? 15.7
69.0 ? 15.7
68.8 ? 16.0
66.8 ? 18.4
relevant group, not the percentage of the total n value. Caseload groups indicate the physician’s sepsis caseload during the 3 years reflected
in the pooled data. The total number of patients was 48,336, and the total number of physicians was 4,888. SD, standard deviation.
Data are no. (%) of subjects, unless otherwise indicated; percentages for all categories other than sex are the percentage of the
trolyte disorders [
cohol abuse [
], lymphoma [ .001
drug abuse [
Table 2 shows the distribution of in-hospital mortality
rates, patient characteristics, and physician characteristics
across septicemia caseload groups. Patients who were treated
by low-caseload physicians had statistically significantly
higher in-hospital mortality rates than did patients treated
by medium-caseload physicians (16.0% vs 12.9%;
high-caseload physicians (16.0% vs 9.7%;
high–caseload physicians (16.0% vs 7.9%;
the 3 years for which data were studied, 4,888 physicians
admitted and treated patients with septicemia; the mean
(?SD) number of admissions was
age of patients was 68.4 years, and that the mean age of
attending physicians was 42.9 years. The mean patient age
was similar across all groups.
Table 3 presents the crude and adjusted odds ratios for in-
hospital mortality, according to the physicians’ septicemia
caseload. The results of the generalized estimating equations
], deficiency anemia [
], depression [
], metastatic cancer [P p .006
], and blood loss anemia [P p .042
P ! .001
P p .004
P ! .001
], AIDS [
P ! .001
P p .002
P ! .001
),P ! .001
), or very
P ! .001
P ! .001
. The mean36.6 ? 54.9
model showed that the adjusted odds of in-hospital mortality
for the patients of low-caseload physicians were approxi-
mately twice the odds of patients treated by very high–case-
load physicians (OR, 1.91 [reciprocal of 0.51];
times the odds of patients treated by high-caseload physicians
( ), and 1.22 times the odds of patients treated by
P ! .001
medium-caseload physicians (
ceipt of treatment from physicians in the very high, high, and
medium caseload groups decreased patients’ odds of in-hos-
pital mortality by 49%, 40%, and 18%, respectively,compared
with the odds for patients treated by low-caseload physicians.
We also found that the critical caseload per physician beyond
which the outcome could not be improved further was 190
P ! .001
). In other words, re-
P ! .001
We found an inverse relationship between the in-hospital
mortality rate and the sepsis caseload of attending physicians
in the present study, which used nationwide, population-
based data for 48,336 patients treated by 4,888 physicians.
560 infection control and hospital epidemiologyjune 2009, vol. 30, no. 6
Septicemia Caseload Group
Crude and Adjusted Odds Ratios for In-Hospital Mortality, According to
Physician’s caseloadCrude OR (95% CI)Adjusted ORa(95% CI)
Low, !39 cases (reference group)
Medium, 39–88 cases
High, 89–176 cases
Very high, 1176 cases
in the pooled data. For all comparisonswiththereferencegroup,
OR, odds ratio.
aAdjusted for attending physician’s age, sex, and specialty; the hospital’s accreditation level; the
patient’s sex, age, and comorbidities (ie, congestive heart failure, valvular disease, peripheral
vascular disorders, hypertension, paralysis, coagulopathy, neurological disorders, chronic pul-
monary disease, uncomplicated diabetes, complicated diabetes, hypothyroidism, renal failure,
liver disease, peptic ulcer, solid tumors without metastasis, fluid and electrolyte disorders, de-
ficiency anemias, AIDS, lymphoma, metastatic cancer, and blood loss anemia); and physician
random effect and hospital random effect (by use of a generalized estimating equations model).
Caseload groups indicate the physician’s sepsis caseload during the 3 years reflected
.CI,confidenceinterval;P ! .001
We provide compelling evidence that physicians with very
high, high, and medium septicemia caseloads decreased pa-
tients’ odds of in-hospital mortality by 49% (95% confidence
interval [CI], 0.41–0.67), 40% (95% CI, 0.53–0.68), and 18%
(95% CI, 0.73–0.92), respectively, compared with the odds
for patients of low-caseload physicians. These findings held
up after partitioning out systematic physician-specific and
hospital-specific variation and isolating the effects of most
hospital, physician, and patient confounders.
This study was one of the first studies of the caseload-
outcome relationship for sepsis treatment, and our results are
broadly consistent with previous findings regarding the as-
sociation between larger caseloads and better outcomes in a
variety of clinical domains, including surgery (eg, vascular,19
general,20and orthopedic surgery21) and treatment of non-
surgical conditions (e.g., pneumonia10and myocardial in-
farction11). With respect to treatment of sepsis in intensive
care units (ICUs), Peelen et al.22found that receipt of treat-
ment in an ICU that had a higher number of patients ad-
mitted with severe sepsis was associatedwithlowerin-hospital
mortality for these patients, compared with those admitted
to an ICU with a lower sepsis case volume. Other studies
have also demonstrated that seriously ill patients admitted to
ICUs that treat a large number of patients have a lower mor-
tality rate than patients admitted to ICUs that treat fewer
patients.23Because patients with sepsis who are in critical
condition are mostly cared for in the ICU, physician practices
and the practices of multidisciplinary ICU teams should be
highlighted to improve sepsis treatment outcomes. Further-
more, we identified a very high caseload (190 cases) beyond
which the outcome could not be further improved, which
indicates that the association between physician caseloadsand
patient outcomes was fairly constant as caseloads increased
up to a very high level.
Several possible explanations have been proposed for the
association between high physician caseloads and improved
treatment outcomes, including the “practice makes perfect”
hypothesis, which suggests that high-caseload physicians may
control unexpected medical conditions and problems better,6
consequently reducing the mortality rate among their pa-
tients. The heterogeneity of the patients with sepsis in our
study (e.g., the causes of their disease, their comorbidities
and complications, and their disease severity at initial pre-
sentation) is reflected in the striking variation in mortality
risk.24Caseload, as a surrogate for experience and quality of
care provided by physicians,5counts considerably toward ef-
fective management of a complex and dynamic disease like
diagnoses and procedures consistently show that patient out-
comes in Taiwan are affected more by physician caseload than
by hospital case volume.25,26The results of our study, in com-
bination with those of other reports, thus support the “prac-
tice makes perfect” hypothesis. An alternative explanation for
these results might be the potentialeffectsofpatients’selective
self-referral to physicians with good reputations. However,
patients with serious septicemia are admitted to an ICU or
the nearest hospital without much time for self-referral. Pa-
tients’ septicemia severity levels should, therefore, be fairly
evenly distributed across physician caseload groups, and thus
self-referral is less likely to affect our findings.
The caseload-outcome relationship we identified has several
implications. Although previous reports have recommended
selective referrals from low- to high-caseload providers,9,27ad-
ditional problems may result from this practice, such as treat-
ical costs resulting from referrals; in addition, there is a lack
of precise criteria for categorizing caseload in each locality.
Thus, in addition to selective referral for severe sepsis cases,
we propose that it is imperative to reduce the variation in the
quality of medical care between low- and high-caseload phy-
sicians. As indicated by Sheikh’s study,28the treatment pro-
cedures adopted by high-caseload physicians should be ex-
amined closely and used to develop more comprehensive
clinical guidelines and protocols for sepsis care, such as com-
caseload and outcomes for sepsis treatment561
petent early recognition of inflammation signs, precise inter-
vention for comorbidities and complications, and appropriate
use of empiric antibiotic treatment,29efficient fluid resuscita-
tion,30and vasoactive drugs.31These guidelines and protocols
could then be used to modify the clinical practices of low-
caseload physicians, thus improving the quality of care and
low-caseload physicians’ cooperation with high-caseload phy-
sicians or introducing telemedicine (ie, remote-access con-
sulting and transfer of information by telephone or the Inter-
net) to remote areas where physicians have low caseloads could
increase experience and the overall quality of care for sepsis
This study has several unique strengths, including the use
of a nationwide, population-based data set. The number of
cases provided sufficient statistical power to detect differences
between groups after adjusting for confounders. Further, it
is generally believed that high-caseload physicians perform
better simply because they practice in better-equipped hos-
pitals. In addition, patients with particular characteristics
might choose and remain with physicians who have specific
characteristics, and thus patients in a physician’s practice
might “cluster.” Our study used a generalized estimating
equations model to allow examination of caseload-outcome
relationships, taking clustering by physician and clustering
by hospital into consideration.14
Two limitations of this study merit attention, however.
First, because we used a claims database, it is possible to
question whether the diagnoses in the database are accurate.
However, the NHI implements routine sampling of patient
records to cross-check each hospital’s claims, and there are
punitive measures in place for fraudulent coding. Illegitimate
increases in the severity of patient diagnoses should therefore
be adequately restrained. This deterrent is further reinforced
by the NHI’s reimbursement system, which requires hospitals
to treat patients from all levels of severityina“fee-for-service”
approach. No documented systematic sensitivity analyses
make diagnostic accuracy a potential limitation, and it is
generally believed that the NHI’s checks and balances pro-
mote accurate coding.
Second, systematic or unmeasured differences in clinical
severity might exist across caseload groups. Nevertheless, pa-
tients’ comorbidities (eg, diabetes mellitus, cardiovascular
disease, or renal disease) should be adequately accounted for
by the use of the Elixhauser Comorbidity Index, which pro-
vides a comprehensive approach to ascertaining a wide set
of comorbidities in administrative data sets without addi-
tional refinement and applies to a broad range of diseases.15
As discussed above, there is little time for patients with sepsis
to self-refer to highly ranked physicians. Selection bias in
terms of disproportionate distributions of patient severity
profiles across caseload groups is thus less likely to have oc-
curred and less likely to have confounded our results.
In summary, our study contributes to the literature by
demonstrating that both more experience in treating sepsis
and a greater sepsis caseload result in substantially lower in-
hospital mortality rates, regardless of the institution. The
“practice makes perfect” hypothesis is thus supported. Rep-
lication of our findings in other countries and settings is
needed to further evaluate the caseload-outcome relationship
for sepsis treatment. Future studies should be performed to
identify modifiable factors (eg, exact clinical processes, phy-
sician practices, and degree of compliance with theguidelines,
such as the Surviving Sepsis Campaign33) that might account
for variation in quality across physician caseload groups. Ef-
fective strategies for improving treatment should be imple-
mented to increase overall competence in sepsis care.
Potential conflicts of interest.
evant to this article.
All authors report no conflicts of interest rel-
Address reprint requests to Herng-Ching Lin, PhD, School of Health Care
Administration, Taipei Medical University, 250 Wu-Hsing St, Taipei 110,
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