Community acquired pneumonia (CAP) shows high mortality rate despite antibiotics treatment. In the US, it is the leading cause of death among infectious diseases, with approximately 5.6 million new cases every year and mortality of 2%-3% (1). In Korea, it ranked 9th among all causes of death in 1999 but jumped to 6th in 2010 which shows the highest mortality among causes of death due to infection included in top 10 causes of death in Korea (2). Mortality due to pneumonia rapidly increases after 45 yr of age and is expected to further increase in the elderly given the accelerating trend of aging population in Korea. Since incidence of pneumonia is higher in the elderly (3) and patients with chronic diseases (4), it is warranted to investigate these high risk groups and pursue intensive management based on such investigation.

Streptococcus pneumoniae (pneumococcus) is known as the most common pathogen causing pneumonia. From a metaanalysis of 127 studies on pathogens of pneumonia, pneumococcal pneumonia accounted for 24% of all cases (5). In a study for 588 pneumonia patients hospitalized in domestic university hospitals, pathogens were identified in 38.3% of cases in which pneumococcal pneumonia represented 21.7% or 57 cases (6). However, identification of a pneumonia pathogen may differ depending on the capacity of the relevant in-hospital laboratory, study design, season or region of the study conduct. In patients who cannot be diagnosed with conventional culture method, S. pneumoniae is identified as the pathogen in approximately 50% of such cases by use of phenotype-specific antibody test. Therefore, the chance of S. pneumoniae being the pathogen is expected to be higher (7). In approximately 40%-60% of pneumonia patients up to date, pathogen has not been identified (8).

Economic burden due to pneumonia depends on patient's age; ≤ 4 or ≥ 70 yr old groups exhibit the highest pneumonia incidence and high admission rate, resulting in the highest economic burden. In Korea, pneumonia patients aged ≥ 65 yr old spend medical costs of Korean Won (KRW) 479.6 billion ever year for pneumonia treatment. This is 6.7 times higher than that in 15-44 yr old pneumonia patient group and 74% of this expense is used for charge of hospitalization (9).

Of pneumococcal diseases, pneumonia accounts for 90% or above, and roughly 5% of cases result in death. In the US, approximately 500,000 new cases of pneumococcal pneumonia are reported every year including approximately 30,000 patients with invasive pneumococcal diseases (sepsis, encephalomeningitis) and overall 20,000 cases of death (10). Given the relatively large number of patients with pneumococcal pneumonia, effective prevention of pneumococcal pneumonia may reduce pneumococcus-induced mortality.

To assess the effectiveness of prevention efforts to reduce pneumonia occurrence, epidemiological data such as incidence, cause of death, and economic burden of pneumonia patients are required primarily. In particular, to investigate the impact on the burden-of-illness, accurate knowledge on economic and clinical indices prior to preventive action would be necessary in confirming the effectiveness after prevention. Nevertheless, there are no sufficient basic data on the level of economic burden resulting from pneumonia in Korea. Although burden of medical costs can be derived from data offered by Health Insurance Review & Assessment Service (HIRA), these data has limitations in that disease codes are not reliable enough, and only insurance claimed charges can be confirmed but not the expenses of uninsured items.

This study investigated the economic burden and baseline epidemiology in Korean pneumonia patients aged ≥ 50 yr. The primary objective was to estimate the economic burden through investigation of direct medical costs incurred from pneumoniarelated utilization of medical institutions, and to obtain epidemiologic data such as patient disposition and death profile in pneumonia patients. The secondary objective was to establish direct medical costs and epidemiology in pneumococcal pneumonia patients only.

This study surveyed patient characteristics and medical costs in 764 pneumonia patients aged ≥ 50 yr who received inpatient care in the Pulmonary Division in 11 medical institutions of general hospital or higher level including local university hospitals. A total of 83.4% of the entire study population had underlying diseases; severity of pneumonia in terms of CURB-65 scores was 1.16 points on average; and S. pneumoniae was identified as the pathogen in 7.4%. Total pneumonia treatment period was 22 days on average and of these, 3.2% patients died during treatment. Total per-capita medical fees for a pneumonia patient were KRW 1,969,303 of which most were incurred as the charge of hospitalization.

In 2010, the mortality due to pneumonia in Korea ranked 6th among all fatal diseases, which is the highest among infectious diseases, warranting various measures to lower the incidence of pneumonia in the future. There are no accurate domestic data available on the incidence and pathogens for pneumonia; this is due to highly difficult diagnosis of atypical pathogens, different test methods used for pathogen diagnosis in each hospital, and different pathogen detection rate by study area or study design. Furthermore, the HIRA data used as the source of epidemiological study on medical cost have weaknesses since reliability on diagnosis is poor and only insurance claims can be confirmed. Given such limitations, this study can provide relatively clear diagnosis of pneumonia since it was conducted in general hospitals and allows accurate calculation of economic expenses by including uninsured spending in the study.

In this study, the pneumonia pathogen was identified in approximately 50% of patients, as in other studies. However, pneumococcus was identified as the cause of pneumonia in 7.4% (15% in patients with an identified pathogen), which was lower than in other studies. The pneumococcal pneumonia rate in Korea has been reported as 13.5% (11) at the lowest when all patients were considered, and 12% (12) in a study in the elderly aged ≥ 65 yr. These rates were higher than the result of this study. The prospective study by Sohn et al. (11), conducted in only 5 institutions in patients aged ≥ 16, made aggressive efforts to detect pathogens by including serology tests. In the study by Yu et al. (12), conducted in a relatively small number of patients (n = 119) in one hospital, the diagnosis rate might have been higher owing to the merit of being conducted in a university hospital.

Pneumococcus and haemophilus tend to be undetected in a sputum culture even shortly after (several hours) antibiotics treatment but this problem can be overcome with the help of a urine antigen test. As this study was conducted only in inpatients ≥ 50 yr mostly in high-level medical institutions, patients are likely to have been prescribed with the first-line antibiotics in local hospitals, possibly resulting in a low pneumococcus detection rate. The low pathogen detection rate might also be attributable to the limitation of a retrospective study.

In this study, the mean treatment period of pneumonia patients was 22 days; 3.2% patients died during treatment; and the pneumonia mortality was approximately 6% for pneumococcal pneumonia. Although the conventional pneumonia treatment period is 7-10 days (13), there have been no sufficient studies on the optimum treatment period and no difference in treatment effect has been reported for shorter treatment duration (14). The reason for a long treatment period in this study is speculated to be the absence of worsening such as the transfer to the ICU during treatment, and inclusion up to the last outpatient visit after a patient's symptom improved, rather than choosing inappropriate antibiotics by considering the low mortality.

In the US, the pneumonia mortality is 2%-3% in all pneumococcal diseases, and approximately 20% in invasive pneumococcal diseases (15). Pneumonia mortality is very high in young children of < 2 yr and the elderly of ≥ 65 yr; the death rate progressively increases from 45 yr and by age 65, it is 60 times higher than that of 30 yr in women, and 40 times higher in men (16). A domestic study in the elderly aged ≥ 65 reported the pneumonia mortality as 28% (12) which warrants intensive management and active preventive efforts for the elderly pneumonia patients. Mortality is also high in chronically ill patients, independently of age-related risks, especially in patients with chronic lung disease, chronic cardiovascular disease, and diabetes (17). For example, the mortality rate increases 4.2-fold in asthma patients, 3.0-fold in lung disease patients and 1.9-fold in cardiovascular disease patients (18). A prospective study in 955 Asian CAP patients has shown that the most common co-morbid conditions were lung disease and cardiovascular disease (19). In this study also, approximately 80% of study subjects had an underlying disease of which chronic cardiovascular disease, chronic lung disease and diabetes were common co-morbid conditions. Given this finding, it would be necessary to implement intensive preventive management in the age group with an identified concurrent underlying disease or a likely co-morbid condition (20).

In pneumococcal-infected patients, the number of pneumonia patients is 17 times higher than that of invasive pneumococcal disease patients. Therefore, we need to focus on pneumonia prevention to lower the overall mortality. Pneumococcal disease is the most common disease for which mortality can be reduced by vaccination. Pneumococcal vaccination rates in young children differ by investigators, ranging from 13% (21) for the single-dose vaccination to approximately 40% vaccination rate in 2007 (22) as estimated in one report. In Korea, adult pneumococcus vaccination is recommended for all adults of ≥ 65 yr or high risk patients aged < 65 yr (23), but public awareness of adult pneumococcus vaccination is low. The adult vaccination rate was 3.4% from a survey of 1,000 adults aged ≥ 65 yr in 15 cities and provinces across the country in 2007. Therefore, it would be crucial to improve the pediatric and adult vaccination rate to reduce the prevalence and mortality of pneumococcal pneumonia as well as the resulting economic burden in Korea. Also, epidemiological data based on accurate diagnosis, as reported in this study, would be critical for accurate judgment of the effectiveness of such strategy.

In this study, total per-capita medical fees were KRW 1,969,303 per pneumonia patient, and medical fees varied by up to 1.5 times among hospitals. This indicates the lack of a physician's willingness to conduct a test or consistent treatment guidelines for pneumonia treatment, rather than the concentration of more severe patients in some hospitals. In Europe, the economic burden of pneumonia is approximately 10 trillion Euros, of which about 60% is spent as the charge of hospitalization, and the economic burden increases with patient's age (24). In 2006, the annual burden-of-illness of pneumococcus (it includes all of the pneumococcal diseases) in Korea was reported as KRW 727.2 billion (9), but as there are no domestic data on pneumococcal incidence, the rationale for this number is weak since this number was calculated by estimating from overseas incidence by age (24). Still, pneumonia accounts for 74% of the entire economic burden of pneumococcal diseases and the burden-ofillness from pneumococcal pneumonia in Korea can be estimated from this number.

For assessment of severity of pneumonia patients, CURB-65 and pneumonia severity index (PSI) are used, and the place of treatment (outpatient, inpatient, ICU admission), selection of antibiotics and prediction of prognosis can be made based on a patient's initial severity (25). PSI is not appropriate for use in a retrospective study due to numerous measurement items. Instead CURB-65 is usually used as it can be readily measured and shows a good correlation with PSI results (26). For patients with the CURB-65 mean score of 1-2 points, hospitalization in a general ward is recommended, and for 3 points, mean mortality rate is 14% and ICU admission is indicated. The mean score for subjects in this study was 1.16, representing the severity that can be treated in a general ward. A retrospective study in 3 university hospitals in Seoul, involving 487 patients aged ≥ 65 yr who were hospitalized due to pneumonia reported the CURB-65 score of mean 1.5 points, similar to this study (27).

The strengths of this study is first of all, accuracy of pneumonia diagnosis as data were surveyed in patients admitted to Pulmonary Division in medical institutions of a general hospital or higher level. Second, pneumonia patients were identified in the reverse temporal order from the treatment completion date of 2010.12.31 in each hospital and were relatively randomly extracted even though this was a retrospective study, resulting in little bias in patient disposition by severity, age, sex, or underlying disease. Third, data calculation was based on confirmation of the accurate medical resource utilization that included uninsured items. Insured items were adjusted for yearly inflation by consistently applying the 2010 insurance fees and the addition by type and nursing (or ICU nursing) personnel category was applied by identifying the actual status in each institution. For uninsured items, the accurate economic burden was calculated by focusing on publicly available uninsured data as disclosed on the website of each institution. Fourth, the study was conducted mostly in referral hospitals (university hospitals), so the assessment of underlying diseases was accurate and there were few transfers to other hospitals, allowing the assessment of treatment outcomes in more than 90% of patients.

There were also limitations in this study. The first limitation is the retrospective study design. Therefore, identification of pathogen strain was not aggressive enough, the level of laboratory facilities and ability of pathogen detection of each center might be different, and may have involved patients who prolonged admission due to other reasons even after pneumonia was treated. Second, as only patients' aged ≥ 50 yr in medical institutions of a general hospital or higher level were included, it may not represent the trend in the entire pneumonia patient population in Korea. Nevertheless, as joint institutions were distributed across the country, it may provide an overall trend.

In summary, this study investigated the characteristics of Korean patients aged ≥ 50 yr who received inpatient care due to pneumonia and the relevant medical costs. When outpatient care was also included, treatment lasted approximately 22 days and KRW 2,000,000 of treatment expenses was incurred on average. This indicates a high level of burden for an individual and society. Given that pneumococcal disease is the most common among infectious diseases for which mortality can be reduced with vaccination, and pneumonia is the most common pneumococcal disease and directly influences mortality, the necessity of vaccination should be stressed. It is revealed that the economic burden of pneumonia is high in Korea, and that the prevention can be considered as an effective strategy.