Etiology of Community-Acquired Pneumonia Surveyed by 7 University Hospitals

Background : Community-acquired pneumonia (CAP) is one of the leading causes of mortality and morbidity, but its management is still challenging. The limitation of diagnostic methods to identify etiologic agents rapidly make it necessary to use empiric antibiotics in almost all patients, and furthermore the discovery of new respiratory pathogens and the emergence of antibiotic-resistant organisms pose difficulties to the selection of an empiric regimen. To clarify the factors necessary for the optimal choice of empirical antibiotics, such as the frequency of etiologic agents, the attributable rates to death and antimicrobial resistance rates in the community, six university hospitals in Seoul and one university hospital in Cheonan were participating in this study. Methods : medical records of adults (>15 years of age) hospitalized for CAP or pulmonary tuberculosis between April 1995 and March 1996, were reviewed. Patients who satisfied all of the following criteria were included in the study: (1) fever or hypothermia; (2) respiratory symptoms; and (3) pulmonary infiltrates on chest roentgenogram. To exclude cases of pulmonary tuberculosis whose roentgenographic features were so typical that it could be easily differentiated from conventional pneumonia, two additional criteria were required for inclusion: antibiotic treatment during the first week of hospital admission and initiation of anti-tuberculosis medications thereafter. Organisms isolated from sterile body sites, acid-fast bacilli or Mycobacterium tuberculosis isolated from sputum, pathogens diagnosed by a 4-fold rising titer of antibodies to “atypical”pathogens, or pathogens revealed by histopathology were defined as definitive cause of pneumonia; isolates from sputum withcompatible Gram stain, pathogens diagnosed by a single diagnostic titer plus use of a specific antimicrobial agent, or tuberculosis diagnosed by clinucal response to anti- tuberculosis medications were considered probable cause of pneumonia. The records of the clinical microbiology were reviewed for isolates of S. pneumoniae, H. influenzae, M. catarrhalis, Mycobacterium or acid-fast bacilli, and Mycoplasma. Then the frequency of these agents, antimicrobial resistance rates of resiratory pathogens from all body sites, and their clinical significance were evaluated. Results: After excluding 365 patients (230 with pulmonary tuberculosis and 135 with CAP) who were screened for inclusion but did not meet the inclusion criteria,246 persons were enrolled in this study. Their mean age was 58.2 years old with slight male predominance (58.2%), and 171(71%) patients had underlying illnesses. Blood cultures were performed on 191 (77.6%) patients and serologic tests on 44(18.3%) patients. The etiologic agents were identified in 31.3%, and the list of individual agents, in decreasing order, was pulmonary tuberculosis (17 definite and 3 probable: data of six hospitals), S. pneumoniae (8 definite and 10 probable), non-pneumococci (3 definite), aerobic gram-negative bacilli (7 definite and 4 probable), Haemophilus spp. (11 probable), mycoplasma (1 definite and 4 probable), polymicrobial infections (2 definite and 2 probable: E. coli and S. agalactiae, M. tuberculosis and S. aureus, S. pneumoniae and H. influenzae and A. baumannii and K. pneumonias), S. aureus (2 definite and 2 probable) , and mucormycosis (1 definite). Among gram-negative bacilli, K. pneumoniae was the most common agent (8isolates). therates of admission to the intensive care unitand of using assisted ventilation were 18% and 9.3%, respectively. The mortality was 13.8% and logistic regression analysis showed that hypothermia and tachypnea were associated with death. Hospital stay averaged 19 days. Susceptible rates of S. pneumoniae isolated from all body sites to penicillin ranged from 8% to 28% but seven isolated from blood of patients with pneumonia were susceptible to penicillin. Also all 8 isolated of k> pneumoniae from patients with pneumonia were susceptible to cefotaxime and gentamicin. Conclusion: In Korea, in addition to S. pneumoniae, M. tuberculosis is an important agent causing community-acquired pneumonia. The low incidence of etiologic diagnosis is probably related to infrequent requesting of test "atypical" pathogens and does not represent the true incidence of infections by "atypical" pathogens, which well be answered by a prospective study. The antimicrobial resistance rates of major respiratory pathogens from sterile body sites are low, however, because of a small number of the isolates this result needs confirmation by a nationwide surveillance of antimicrobial resistance.ope