To the Editor: Hospitalization for community-acquired pneumonia (CAP) in elderly people is associated with high mortality and with a high rate of readmission.1, 2 The recent data suggest that aspiration pneumonia due to silent aspiration is an important mechanism for the pathogenesis of pneumonia in older people.3-5 Although the importance of aspiration as a frequent mechanism of CAP and hospital-acquired pneumonia (HAP is well known), the incidence of aspiration pneumonia in hospitalized patients has not been fully elucidated. Because the aged population is growing rapidly in developed countries, most hospitalized patients with pneumonia are older patients, who are likely to experience unwitnessed aspiration of oropharyngeal contents during the night. We prospectively assessed the prevalence of aspiration pneumonia in CAP and HAP in hospitalized patients in 22 hospitals in different areas of Japan. Five hundred eighty-nine patients aged 2 to 101 (mean age±standard deviation 72.6±8.2; 377 men, 212 women) were studied between April 2004 and April 2005. Pulmonologists treated the hospitalized patients. No patients died in the hospital. In the current study, aspiration pneumonia was defined according to the Japanese Study Group on Aspiration Pulmonary Disease definition as pneumonia in a patient with a predisposition to aspiration because of dysphagia or swallowing disorders. Swallowing function was assessed using the water swallowing test, repetitive saliva swallowing test, simple-swallowing provocation test, and videofluorography.6, 7 The swallowing function testing was used for the diagnosis of aspiration pneumonia. When swallowing function was not assessed using these examinations, the presence of overt symptoms of dysphagia or the medical history of aspiration was determined as the swallowing disorders in the patients. Pneumonia was diagnosed by the presence of pulmonary infiltration on chest radiograph and computed tomography (CT) and according to systemic inflammation as determined according to blood analyses of white blood cell (WBC) count and C-reactive protein (CRP). The criteria for pneumonia were established according to the pneumonia guidelines of Japan Respiratory Society.8 Patients with pneumonia treated by another hospital before hospitalization in the study hospitals were excluded. Patients with severe complications and known allergies to the tested antibiotics, ands those who had received other antibiotic therapies within 1 month before enrollment were also excluded. Patients with end-stage cancers or life-threatening serious disease or acute respiratory distress syndrome or sepsis were not included the study. In the current study, most of the patients hospitalized for pneumonia were elderly (Figure 1). Seventy-five percent of the hospitalized patients with pneumonia were aged 70 and older. The ratio of aspiration pneumonia to total cases of pneumonia increased with age (Figure 2). Aspiration pneumonia is common in patients aged 70 and older. Three hundred six of 382 pneumonia patients aged 70 and older (80.1%) were diagnosed with aspiration pneumonia. The incidence of hospitalized pneumonia according to age; 589 cases were analyzed. The ratio of aspiration pneumonia (ASP) and any type of pneumonia except aspiration pneumonia (non-ASP) in total hospitalized pneumonia according to age. The incidence of aspiration pneumonia in CAP and HAP was 60.1% (264/439 cases) and 86.7% (130/150 cases), respectively. Three hundred ninety-four patients of 589 patients hospitalized for pneumonia (66.8%) were diagnosed with aspiration pneumonia. A swallowing function testing was performed on 361 patients (61.2%) in the current study. The water swallowing test was most frequently performed. Three hundred forty-four of 589 patients (58.4%) were examined using the water swallowing test. The repetitive saliva swallowing test and the simple-swallowing provocation test were used for approximately 20% of the patients. Only 6.2% of the patients with pneumonia were examined using videofluography. This study revealed that aspiration pneumonia was common in CAP and HAP in hospitalized patients. Although the hospitalized patients were older, the incidence of aspiration pneumonia is high, which had not been previously speculated. It has recently been reported that aspiration pneumonia is often observed in elderly patients with CAP.5 Furthermore, the Perindopril Protection Against Recurrent Stroke Study (PROGRESS) found that angiotensin-converting enzyme inhibitors, which improve swallowing function, are effective in reducing the rate of aspiration pneumonia in Asian patients with a history of stroke but not in Caucasians.9 Because the participants in the PROGRESS study were outpatients with a history of stroke but without overt neurological deficit, it is reasonable to speculate that silent aspiration and minor swallowing disorders after stroke cause aspiration pneumonia, and angiotensin-converting enzyme inhibitors induce improvement of swallowing function, which may contribute to a reduction in the frequency of pneumonia in otherwise healthy elderly subjects with a history of stroke. There are limitations of this study. Although it is a prospective multicenter study, the sample size was not large. Second, the swallowing function testing was not uniformly performed on all patients. Third, the study did not include bacterial examination. Furthermore, the pulmonary physicians in each hospital selected therapeutic regimens. Although treatment with antibiotics is necessary to clinically cure CAP and HAP in elderly patients, recent data have revealed that oral care and swallowing rehabilitation are effective in preventing repeated aspiration pneumonia.10 This evidence has suggested that dysphagia and swallowing abnormality may be primarily a mechanism of aspiration pneumonia in elderly people. Thus, in addition to antibiotic treatment, a preventive strategy based on aspiration-related mechanisms in the development of pneumonia may be important for hospitalized elderly patients. In conclusion, the incidence of aspiration pneumonia as determined according to swallowing function testing was high in CAP and HAP in hospitalized patients. This indicates that the therapeutic and management approach for aspiration pneumonia may be necessary in the treatment guidelines for CAP and HAP in elderly people. Combined teams of geriatricians and infectious diseases and pulmonary specialists are likely to improve the quality of care in this situation. The high incidence of aspiration pneumonia also indicates that oral care and rehabilitation of swallowing disorders may be the key to prevention of CAP and HAP. Conflict of Interest: The editor in chief has reviewed the personal and financial checklist provided by the authors and has determined that none of the authors have any conflicts related to this letter. Dr. Teramoto was supported by a research grant from Mitsui Life Social Welfare Foundation Japan fund and by research grant from Mitsukoshi Health and Welfare Foundation in Japan. Author Contributions: Shinji Teramoto: study concept and design. Yoshinosuke Fukuchi, Hidetada Sasaki, Koichi Sato, Kiyoihsa Sekizawa, Takeshi Matsuse: acquisition of subjects and/or data, analysis. Hidetada Sasaki and Kiyoihsa Sekizawa: interpretation of data. Shinji Teramoto: preparation of manuscript. Sponsor's Role: Pfizer Japan Inc. supported the data collection and analysis. The sponsor had no role in the design, methods, recruitment, or preparation of this letter.
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Teramoto et al. (2008) studied this question.
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