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Clinical Investigations: COMMUNITY-ACQUIRED PNEUMONIA |

Treatment Costs of Community-Acquired Pneumonia in an Employed Population* FREE TO VIEW

Gene L. Colice, MD, FCCP; Melissa A. Morley, MA; Carl Asche, PhD; Howard G. Birnbaum, PhD
Author and Funding Information

*From the Pulmonary, Critical Care and Respiratory Services (Dr. Colice), Washington Hospital Center, Washington, DC; Analysis Group (Ms. Morely and Dr. Birnbaum), Boston, MA; and Aventis Pharmaceuticals (Dr. Asche), Bridgewater, NJ.

Correspondence to: Gene L. Colice, MD, FCCP, Director, Pulmonary, Critical Care and Respiratory Services, Washington Hospital Center, 110 Irving St NW, Washington, D.C. 20010; e-mail Gene.Colice@Medstar.net



Chest. 2004;125(6):2140-2145. doi:10.1378/chest.125.6.2140
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Published online

Background: Community-acquired pneumonia (CAP) is a serious clinical problem, causing hospitalization in about 20% of cases and death in up to 16% of hospitalized patients. Work-loss cost estimates indicate that the treatment of CAP also has a large economic impact. The purpose of this study was to assess the medical and prescription drug (treatment) costs of managing CAP in an employed population.

Method: The costs of CAP were determined from an administrative claims database covering the years 1996 to 1998 for an employed population and their dependents [65 years of age (100,000 population)]. Treatment costs for managing both inpatient and outpatient cases of CAP were calculated from payments by the health plan.

Results: A total of 7,249 episodes of CAP among 6,415 individuals were identified. The hospitalization rate was 19.6%, and the mortality rate for those hospitalized was 9.1%. Patients requiring hospitalization were older and had more comorbid conditions. The mean (± SD) treatment cost for an inpatient episode of CAP (including all inpatient and outpatient medical care) was $10,227 ± 15,342. The costs for inpatients who died during hospitalization (mean cost, $15,822 ± 26,541) were higher than for episodes in which patients were discharged from the hospital alive (mean cost, $9,595 ± 13,641). The mean treatment cost for an outpatient episode of CAP was $466 ± 1,038.

Conclusions: The treatment cost of managing CAP in this employed population was higher than previously estimated. It is estimated that the annual cost of treating CAP in the United States is $12.2 billion.

Figures in this Article

There may be up to 5 to 6 million cases of community-acquired pneumonia (CAP) diagnosed annually in the United States, accounting for > 1 million hospitalizations and approximately 10 million physician visits.13 In large database evaluations, a meta-analysis of the literature, and a prospective survey,47 the average mortality rate for patients hospitalized with CAP has ranged from 8.8 to 15.8%. Clearly, CAP is an important clinical problem.

Managing CAP also has a large economic impact. It has been estimated that it costs $8.4 billion per year (in 1995 dollars) to treat CAP in the United States.1 However, this cost estimate and others3,5,8have been based on methods that involve converting either Medicare charges or hospital bills to costs through Medicare cost/charge ratios. We have previously established claims database methods to determine the economic impact of pneumonia and other respiratory infections on a comprehensive health-care plan covering an employed population.912 From this database, we were able to calculate payments by the employer’s benefit program for multiple components of health care, including costs for hospitalization, outpatient visits, prescription drugs, disability, and absenteeism. Our initial analyses concentrated on annual average costs to the health plan for beneficiaries with respiratory infections. We now extend our analysis of this database to examine the treatment costs of individual episodes of CAP. These costs can be used to estimate the total annual treatment costs of CAP in the United States.

The data for this analysis come from an employer administrative claims database that includes 1996 to 1998 medical and pharmaceutical claims for > 100,000 employees and dependents of a national Fortune 100 manufacturer that were provided by a third-party aggregator of claims data (CORE Inc; Portland, ME). The employer offers comprehensive health insurance and has a predominantly unionized workforce. Beneficiaries were distributed across the country and were enrolled in one of the managed indemnity insurance plans of this company. The beneficiaries included both employees and dependents. Employees included a wide range of managerial, professional, industrial, and office-based workers. Data for those beneficiaries enrolled in health maintenance organizations (who accounted for approximately 20% of enrollees) were not available, and these individuals were excluded from the sample. To ensure completeness of the records, subjects ≥ 65 years in 1998 were excluded due to their enrollment in Medicare.

Medical claims include information on the date of service and the nature of the ailments, as described by detailed diagnosis codes (ie, International Classification of Diseases, ninth revision) and procedure codes (ie, current procedural terminology). Similarly, prescription drug claims (which are available on an outpatient basis) include National Drug Code information. All patients in the database with one or more claims for pneumonia (International Classification of Diseases, ninth revision, codes 480.X to 486.X) during the period 1996 to 1998 were identified. Episodes of hospital-acquired pneumonia were excluded from the analysis. An episode of pneumonia was defined as being hospital-acquired if the individual had an inpatient hospital claim within 2 weeks prior to the first date of a pneumonia episode. The remaining episodes were identified as CAP. A drug claim for an anti-infective agent during a CAP episode was required for inclusion in the outpatient analysis. This criterion was not imposed in the inpatient analysis because inpatient pharmaceutical data were not available. Individuals also were excluded from the analysis if they had received a diagnosis of HIV infection, tuberculosis, or cystic fibrosis, or had received an organ or bone marrow transplant during the 3-year study period.

Because patients may have been treated for CAP more than once during the 3-year study period, episodes rather than individuals were the unit of analysis. All pneumonia claims occurring within < 30 days of each other were assigned to the same episode. The date on the first pneumonia claim in each series was defined as the episode start date. The date on the last pneumonia claim in this series plus 30 days (to account for possible follow-up care that may not have been coded specifically for pneumonia) was defined as the end date of the episode. A new episode of pneumonia was assigned when there were > 30 days between pneumonia claims. Only full episodes were included in the analysis. Therefore, we incorporated a 30-day washout period at the start of 1996 and at the end of 1998 to allow for the analysis of full episodes of care.

Total treatment costs (defined as employer payments to providers for medical care) for an inpatient CAP episode (including all inpatient and outpatient medical care) were calculated separately for episodes in which patients were discharged alive from the hospital and for episodes in which patients died during hospitalization. Costs were expressed as the mean cost ± SD per CAP episode. To better illustrate the distribution of treatment costs over the entire range, the mean cost per CAP episode also was calculated by quintiles. For example, the top quintile is the 20% of CAP episodes with the highest costs. Because there was no death indicator in the data set, death during hospitalization was defined by the absence of medical claims following the last date of hospitalization during an episode of CAP. In order to correctly assign death during a hospitalization, we required that the last date of hospitalization be on or before December 1, 1998. Total treatment costs, which were calculated as payments to providers for all outpatient hospital, physician office, and prescription drug costs, and did not include insurance premiums, deductibles, or other out-of-pocket expenses, were determined separately for CAP outpatient episodes.

Patient demographics, including age and gender, were summarized for patients treated on an outpatient basis, for inpatients with CAP who were discharged from the hospital alive, and for inpatients with CAP who died during hospitalization. The Charlson comorbidity index was calculated for each of these patient groups as a measure of the severity of illness and to identify the presence of relevant comorbid illness.13 The Charlson index is a validated method of classifying comorbidity and severity of illness. The index is the total of assigned weights, based on the presence of a number of major conditions that are present among the diagnoses on patients’ medical claims. Patients were assigned a comorbidity score based on the presence of a claim with a diagnosis for one of the comorbidities in the Charlson index at any time from 1996 to 1998. Differences in demographics and baseline characteristics between groups were compared using t tests for the differences between sample means and χ2 tests for the differences in sample proportions. All statistical analyses were performed using a statistical software package (SAS, version 8; SAS Institute; Cary, NC).

Over the 3-year study period, a total of 7,249 episodes of CAP among 6,415 individuals was identified in the claims database. A total of 5,256 patients had 5,827 outpatient CAP episodes, and 1,329 patients had 1,422 CAP episodes requiring hospitalization. Nine percent of patients had more than one outpatient CAP episode, 7% of patients had more than one inpatient CAP episode, and 3% of patients had at least one inpatient and one outpatient CAP episode. The hospitalization rate among CAP episodes was 19.6% (1,422 of 7,249 episodes), and the mortality rate among inpatient CAP episodes was 9.1% (129 of 1,422 episodes).

Patients requiring hospitalization for an episode of CAP were older than patients with outpatient CAP and had more comorbid conditions (Table 1 ). The average Charlson comorbidity index score was significantly higher for inpatients who were discharged alive from the hospital than for outpatients (p < 0.0001). Although there was a trend for the Charlson comorbidity index to be higher in inpatients who died than in inpatients who were discharged from the hospital alive, the difference was not statistically significant (p = 0.0799). Inpatients with CAP who died were significantly less likely to have chronic pulmonary disease, but were significantly more likely to have tumors and lymphoma than inpatients with CAP who were discharged from the hospital alive.

The mean treatment cost for an inpatient episode of pneumonia (including all inpatient and outpatient medical care during the pneumonia episode) was $10,227 ± 15,342. The costs for patients who died during hospitalization ($15,822 ± 26,451) were higher than for episodes in which patients were discharged from the hospital alive ($9,595 ± 13,641) [Fig 1] . However, the cost differential by hospital discharge status (ie, alive or dead) was present only for the most expensive 20% (quintile 5) of all inpatient CAP episodes. In quintile 5, the mean cost for inpatient episodes in which the patients were discharged from the hospital alive was $28,216 ± 22,858 compared to $41,421 ± 37,012 for episodes in which patients died during hospitalization. When this cost analysis was repeated in patients who had no comorbid conditions, different results were found (Fig 2 ). The mean cost of treating an inpatient episode of CAP was lower ($6,372 ± 13,355). Costs for patients who were discharged from the hospital alive were higher ($6,547 ± 14,070) than those for patients who died during hospitalization ($4,881 ± 5,269), and in quintile 5 costs were also higher for those discharged from the hospital alive ($18,642 ± 28,355) than for those who died ($13,802 ± 5,087).

The mean treatment cost per outpatient CAP episode was $466 ± 1,038 (Fig 3 ). The most expensive episodes, found in quintile 5, cost an average of $1,540 ± 1,974, while those in the less expensive quintiles had mean costs of between $74 ± 22 and $367 ± 70. Of the medical costs for all outpatient CAP patients, 62% were for outpatient hospital charges, 25% were for physician office visits, and 13% were for prescription drugs.

This is the first analysis to provide estimates of treatment costs for hospitalized and nonhospitalized, non-Medicare patients with CAP based on payments from the employer. This information extends our previous work, which examined the average annual costs attributed to respiratory infections,912 and compliments previously published information on the costs of CAP, which have been indirectly derived from either the Medicare claims database1,45 or hospital billing records.8,14

A well-established method, based on determining payments to providers from a comprehensive, employer-based insurance plan, has been used to calculate treatment costs in this analysis.912 This method expresses costs in a way that is easily understandable to employers, which is important because employers, through private group health insurance programs, currently provide coverage to approximately 62% of the employed US population.15 Providing information to employers on payments made to providers as a direct measure of costs is preferable to extrapolating costs by collecting charges from either the Medicare claims database or hospital billing records and multiplying the costs by the Medicare cost/charge ratio. The approach used in this analysis also has the advantage of access to both inpatient and outpatient payments from a single system without the inherent inconsistencies of imputation across multiple data sources.

In this analysis, the average cost to the employer for a patient hospitalized with CAP was $10,227. Although Whittle et al5 reported similar mean costs of $9,581 for Medicare patients hospitalized with CAP in Pennsylvania in 1990, most other studies have estimated lower average costs for a patient hospitalized with CAP. Using national survey data, Niederman et al1 found that the cost of a hospital stay for CAP (in 1995 dollars) was $6,042 for patients < 65 years of age and $7,166 for Medicare patients. Kaplan and colleagues,4 analyzing 1997 Medicare data, reported a mean cost of $6,949 per episode of hospitalized CAP. Fine et al8 reported that median costs in 1997 for a patient hospitalized with CAP ranged from $5,382 to $7,341 across four different hospitals. Others have shown that, although average charges may range from $9,979 to $12,467 for hospital care of patients with CAP,1618 adjusted costs will generally be < $7,000.16,1819

The difference in costs for treating CAP between this study and previous work may be explained by the direct methods used for capturing payments in this analysis. It should also be noted that the costs in this analysis were driven to a large extent by a small proportion of patients (ie, those in quintile 5) who generated extremely high costs. Some authors have excluded charge outliers from their analyses.8 However, costs may be very high for a small segment of the CAP population, and these should be included. Angus et al14 showed that patients with CAP requiring admission to an ICU generated much higher median costs ($21,144) than did those for patients not requiring intensive care (median costs, $5,785). In the present study, hospitalized patients who died generated higher costs than did those patients who were discharged from the hospital alive, except for the very small number of patients who died and had no comorbid conditions. Previous studies4,14,16 also have shown that nonsurvivors generated higher costs than survivors.

The population studied in this analysis, employees < 65 years of age and their dependents, represent the majority of the US population and, consequently, reflect a substantial proportion of the cases of CAP occurring in the United States. To the extent that the US population is generally similar to the population studied in both the incidence of CAP and health-care utilization costs, it is possible to estimate the total annual costs for managing CAP in the United States. Based on a 1997 US population estimate of 270 million people and an incidence rate of CAP of 1.9% in this population,10 5.1 million cases of CAP occur annually in the United States (270 million × 1.9%), resulting in 1 million hospitalizations (5.1 million × 19.6% hospitalization rate for CAP) and 91,000 deaths (1 million hospitalized patients × 9.1% mortality rate for hospitalized CAP patients). The total inpatient treatment cost for CAP based on these data would be $10.3 billion (1 million hospitalizations × $10,227 average cost per CAP inpatient). Because the costs for treating outpatients with CAP in our analysis were substantially lower than those for inpatients, the total outpatient treatment cost for CAP would be $1.9 billion (4.1 million outpatients × $466 average cost per CAP outpatient). Thus, from this analysis the total annual cost of treating CAP in the United States for the years 1996 to 1998 can be estimated at $12.2 billion. However, this figure is most probably an underestimate of the actual economic impact of CAP. The incidence of pneumonia1,3 and the number of comorbid conditions increase with age, suggesting that treatment costs would have been higher if patients ≥ 65 years of age had been included in the analysis. The current analysis also did not account for other costs of illness to the employer, such as disability and absenteeism. Including these factors would have added substantially to the overall economic burden of treatment for CAP.10 It was not possible to partition costs between those directly related to CAP and those due to comorbid illnesses. Our previous work10 with this database showed that the portion of the costs that is specifically related to the treatment of pneumonia might be small, suggesting that comorbid conditions generate a large portion of the costs of a hospitalization initially precipitated by CAP.

There are well-recognized limitations of administrative claims data sets, such as possibly inaccurate diagnoses and incomplete assembly of claims (eg, missing bills or multiple plan coverage). Our data on hospitalization rates, mortality rates, and the incidence of CAP compare well with previous estimates, reassuring us that the methods used to identify patients with CAP in this database were effective. Over the 3-year study period in this analysis, approximately 20% of the patients experiencing CAP episodes required hospitalization, which is a rate comparable to that described previously.23 Hospitalized patients were older and more often had comorbid conditions. The relationship between comorbid conditions and mortality has been reported previously.2,5 Mortality rates for patients with CAP vary by severity,20 but on average the mortality rate for hospitalized CAP patients has ranged from 8.8 to 15.8%.47 In this analysis, 9.1% of hospitalized patients with CAP died. The mortality rates described in this analysis would presumably have been higher if patients > 65 years of age had been included, as there is a direct relationship between increasing mortality and age.20 We have previously reported that the incidence of CAP was 1.9% in this population,10 which is slightly lower than estimates from the Medicare population.1,4

In summary, the treatment costs for the inpatient and outpatient management of CAP have been determined from a claims database of employed people and their dependents < 65 years of age. From these data, it is possible to extrapolate that there are 5.1 million cases of CAP annually in the United States, resulting in 1 million hospitalizations and 91,000 deaths. The annual costs for treating outpatient and inpatient cases of CAP from 1996 to 1998 is estimated to have been $12.2 billion. This estimate is substantially higher than that previously reported but still might underestimate the actual annual economic impact of CAP.

Abbreviation: CAP = community-acquired pneumonia

Dr. Colice has acted as a consultant to Aventis Pharmaceuticals in other capacities. Dr. Birnbaum and Ms. Morley were supported by an unrestricted grant from Aventis Pharmaceuticals. Dr. Asche is a full-time employee of Aventis Pharmaceuticals.

Table Graphic Jump Location
Table 1. Demographics and Charlson Comorbidities
* 

Statistically significant differences (p < 0.05) between outpatients with CAP and inpatients with CAP discharged alive. t Tests for the difference between sample means and chi-square tests for differences in sample proportions were calculated.

 

Statistically significant differences (p < 0.05) between inpatients with CAP discharged alive and inpatients with CAP who died. t Tests for the difference between sample means and χ2 tests for differences in sample proportions were calculated.

Figure Jump LinkFigure 1. Mean treatment expenditures per episode for inpatients with CAP, by quintile (patients discharged from the hospital alive vs patients who died).Grahic Jump Location
Figure Jump LinkFigure 2. Mean treatment expenditures per episode for inpatients with CAP, by quintile (patients with no comorbid conditions and patients discharged from the hospital alive vs patients who died).Grahic Jump Location
Figure Jump LinkFigure 3. Mean treatment expenditures per episode, by quintile for outpatient CAP (5,827 episodes). Rx = treatment; MD = physician.Grahic Jump Location
Niederman, MS, McCombs, JS, Unger, AN, et al (1998) The cost of treating community-acquired pneumonia.Clin Ther20,820-837. [CrossRef] [PubMed]
 
Niederman, MS, Mandell, LA, Anzueto, A, et al Guidelines for the management of adults with community-acquired pneumonia: diagnosis, assessment of severity, antimicrobial therapy, and prevention.Am J Respir Crit Care Med2001;163,1730-1754. [PubMed]
 
Bartlett, JG, Dowell, SF, Mandell, LA, et al Practice guidelines for the management of community-acquired pneumonia.Clin Infect Dis2000;31,347-382. [CrossRef] [PubMed]
 
Kaplan, V, Angus, DC, Griffin, MF, et al Hospitalized community-acquired pneumonia in the elderly.Am J Respir Crit Care Med2002;165,766-772. [PubMed]
 
Whittle, J, Lin, CJ, Lave, JR, et al Relationship of provider characteristics to outcomes, process, and costs of care for community-acquired pneumonia.Med Care1998;36,977-987. [CrossRef] [PubMed]
 
Fine, MJ, Smith, MA, Carson, CA, et al Prognosis and outcomes of patients with community-acquired pneumonia.JAMA1995;274,134-141
 
Marston, BJ, Plouffe, JF, File, TM, et al Incidence of community-acquired pneumonia requiring hospitalization.Arch Intern Med1997;157,1709-1718. [CrossRef] [PubMed]
 
Fine, MJ, Pratt, HM, Obrosky, DS, et al Relation between length of hospital stay and costs of care for patients with community-acquired pneumonia.Am J Med2000;109,378-385. [CrossRef] [PubMed]
 
Birnbaum, HG, Cremieux, PY, Greenberg, PE, et al Using healthcare claims data for outcomes research and pharmacoeconomic analyses.Pharmacoeconomics1999;16,1-8
 
Birnbaum, HG, Morley, M, Greenberg, PE, et al Economic burden of pneumonia in an employed population.Arch Intern Med2001;161,2725-2731. [CrossRef] [PubMed]
 
Birnbaum, HG, Morley, M, Greenberg, PE, et al Economic burden of respiratory infections in an employed population.Chest2002;122,603-611. [CrossRef] [PubMed]
 
Birnbaum, HG, Morley, M, Leong, S, et al Lower respiratory tract infections.Pharmacoeconomics2003;21,749-759. [CrossRef] [PubMed]
 
Charlson, ME, Pompei, P, Ales, KL, et al A new method of classifying prognostic comorbidity in longitudinal studies: development and validation.J Chronic Dis1987;40,373-383. [CrossRef] [PubMed]
 
Angus, DC, Marrie, TJ, Obrosky, DS, et al Severe community-acquired pneumonia.Am J Respir Crit Care Med2002;166,717-723. [CrossRef] [PubMed]
 
Health Affairs. Number of Americans with job-based health benefits grew through early 2001 despite higher benefit costs. January 8, 2002. Available at: http://www.healthaffairs.org/press/janfeb0202.htm. Accessed May 14, 2004.
 
Lave, JR, Fine, MJ, Nankey, SS, et al Hospitalized pneumonia.J Gen Intern Med1996;11,415-421. [CrossRef] [PubMed]
 
Kessler, LA, Waterer, GW, Barca, R, et al Pharmaceutical industry research and cost savings in community-acquired pneumonia.Am J Manag Care2002;8,798-800. [PubMed]
 
Brown, RB, Iannini, P, Gross, P, et al Impact of initial antibiotic choice on clinical outcomes in community-acquired pneumonia.Chest2003;123,1503-1511. [CrossRef] [PubMed]
 
Paladino, JA, Gudgel, LD, Forrest, A, et al Cost-effectiveness of IV-to-oral switch therapy.Chest2002;122,1271-1279. [CrossRef] [PubMed]
 
Fine, MJ, Auble, TE, Yealy, DM, et al A prediction rule to identify low-risk patients with community-acquired pneumonia.N Engl J Med1997;336,243-250. [CrossRef] [PubMed]
 

Figures

Figure Jump LinkFigure 1. Mean treatment expenditures per episode for inpatients with CAP, by quintile (patients discharged from the hospital alive vs patients who died).Grahic Jump Location
Figure Jump LinkFigure 2. Mean treatment expenditures per episode for inpatients with CAP, by quintile (patients with no comorbid conditions and patients discharged from the hospital alive vs patients who died).Grahic Jump Location
Figure Jump LinkFigure 3. Mean treatment expenditures per episode, by quintile for outpatient CAP (5,827 episodes). Rx = treatment; MD = physician.Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1. Demographics and Charlson Comorbidities
* 

Statistically significant differences (p < 0.05) between outpatients with CAP and inpatients with CAP discharged alive. t Tests for the difference between sample means and chi-square tests for differences in sample proportions were calculated.

 

Statistically significant differences (p < 0.05) between inpatients with CAP discharged alive and inpatients with CAP who died. t Tests for the difference between sample means and χ2 tests for differences in sample proportions were calculated.

References

Niederman, MS, McCombs, JS, Unger, AN, et al (1998) The cost of treating community-acquired pneumonia.Clin Ther20,820-837. [CrossRef] [PubMed]
 
Niederman, MS, Mandell, LA, Anzueto, A, et al Guidelines for the management of adults with community-acquired pneumonia: diagnosis, assessment of severity, antimicrobial therapy, and prevention.Am J Respir Crit Care Med2001;163,1730-1754. [PubMed]
 
Bartlett, JG, Dowell, SF, Mandell, LA, et al Practice guidelines for the management of community-acquired pneumonia.Clin Infect Dis2000;31,347-382. [CrossRef] [PubMed]
 
Kaplan, V, Angus, DC, Griffin, MF, et al Hospitalized community-acquired pneumonia in the elderly.Am J Respir Crit Care Med2002;165,766-772. [PubMed]
 
Whittle, J, Lin, CJ, Lave, JR, et al Relationship of provider characteristics to outcomes, process, and costs of care for community-acquired pneumonia.Med Care1998;36,977-987. [CrossRef] [PubMed]
 
Fine, MJ, Smith, MA, Carson, CA, et al Prognosis and outcomes of patients with community-acquired pneumonia.JAMA1995;274,134-141
 
Marston, BJ, Plouffe, JF, File, TM, et al Incidence of community-acquired pneumonia requiring hospitalization.Arch Intern Med1997;157,1709-1718. [CrossRef] [PubMed]
 
Fine, MJ, Pratt, HM, Obrosky, DS, et al Relation between length of hospital stay and costs of care for patients with community-acquired pneumonia.Am J Med2000;109,378-385. [CrossRef] [PubMed]
 
Birnbaum, HG, Cremieux, PY, Greenberg, PE, et al Using healthcare claims data for outcomes research and pharmacoeconomic analyses.Pharmacoeconomics1999;16,1-8
 
Birnbaum, HG, Morley, M, Greenberg, PE, et al Economic burden of pneumonia in an employed population.Arch Intern Med2001;161,2725-2731. [CrossRef] [PubMed]
 
Birnbaum, HG, Morley, M, Greenberg, PE, et al Economic burden of respiratory infections in an employed population.Chest2002;122,603-611. [CrossRef] [PubMed]
 
Birnbaum, HG, Morley, M, Leong, S, et al Lower respiratory tract infections.Pharmacoeconomics2003;21,749-759. [CrossRef] [PubMed]
 
Charlson, ME, Pompei, P, Ales, KL, et al A new method of classifying prognostic comorbidity in longitudinal studies: development and validation.J Chronic Dis1987;40,373-383. [CrossRef] [PubMed]
 
Angus, DC, Marrie, TJ, Obrosky, DS, et al Severe community-acquired pneumonia.Am J Respir Crit Care Med2002;166,717-723. [CrossRef] [PubMed]
 
Health Affairs. Number of Americans with job-based health benefits grew through early 2001 despite higher benefit costs. January 8, 2002. Available at: http://www.healthaffairs.org/press/janfeb0202.htm. Accessed May 14, 2004.
 
Lave, JR, Fine, MJ, Nankey, SS, et al Hospitalized pneumonia.J Gen Intern Med1996;11,415-421. [CrossRef] [PubMed]
 
Kessler, LA, Waterer, GW, Barca, R, et al Pharmaceutical industry research and cost savings in community-acquired pneumonia.Am J Manag Care2002;8,798-800. [PubMed]
 
Brown, RB, Iannini, P, Gross, P, et al Impact of initial antibiotic choice on clinical outcomes in community-acquired pneumonia.Chest2003;123,1503-1511. [CrossRef] [PubMed]
 
Paladino, JA, Gudgel, LD, Forrest, A, et al Cost-effectiveness of IV-to-oral switch therapy.Chest2002;122,1271-1279. [CrossRef] [PubMed]
 
Fine, MJ, Auble, TE, Yealy, DM, et al A prediction rule to identify low-risk patients with community-acquired pneumonia.N Engl J Med1997;336,243-250. [CrossRef] [PubMed]
 
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