title: [A retrospective cohort study of the influence of time of hospital-acquired pneumonia onset on pathogen constitution].
abstract: OBJECTIVE
  To study the influence of duration of hospitalization on etiologic agent and antibiotic-resistance of hospital-acquired pneumonia (HAP).
  
  
  METHODS
  Cases of HAP were patients hospitalized in Fudan University Zhongshan Hospital, Ruijin Hospital, Beijing Hospital, Zhongshan University Affiliated Third Hospital, Guangzhou Medical College Affiliated Hospital and Guangdong People's Hospital. These patients were hospitalized from January 2001 to December 2003, and the diagnosis of HAP was made based on positive respiratory specimen cultures. Clinical data including time of HAP onset, severity of illness, risk factors, isolated bacteria and antimicrobial susceptibility were collected and analyzed. Statistical analysis was performed with the SPSS 12.0 software.
  
  
  RESULTS
  A total of 562 cases of HAP were recruited, including 136 cases of early-onset pneumonia (time of onset < or = 5 d), 326 cases of middle-onset pneumonia (time of onset 6 - 14 d) and 100 cases of late-onset pneumonia (time of onset > or = 15 d). The rate of prior antibiotic use increased from 68.4% in the early-onset group to 88.0% in the late-onset group (P = 0.002); ICU admission increased from 29.4% to 46.0% (P = 0.03), and immunosuppression increased from 1.5% to 15% (P = 0.001). A total of 918 strains of bacteria were isolated, the most common pathogens being Pseudomonas aeruginosa (18.6%), Staphylococcus aureus (16.1%), Acinetobacter spp (16.1%), Klebsiella spp (14.4%) and Enterobacter spp (8.8%). Early-onset HAP were more commonly caused by Klebstella (18.3%), while the main etiologic agents for late-onset HAP were Pseudomonas aeruginosa (24.2%) and Methicillin-resistant Staphylococcus aureus (19.3%). The rates of pneumonia caused by Haemophilus and Streptococcus were 4.3% and 2.4% respectively in the early-onset cases, but none was found in late-onset cases. The antibacterial activity of ceftriaxone was influenced by duration of hospitalization, risk factors and severity of the disease. In less severe early-onset cases without risk factors, the sensitivity of ceftriaxone was 80%. But in severe late-onset cases, it was only 50%.
  
  
  CONCLUSIONS
  There was significant difference in the pathogen constitution and antibiotic-resistance among early-onset, middle-onset and late-onset cases of HAP. The sensitivity of ceftriaxone was high in less severe early-onset cases without risk factors.
authors.affiliation: Department of Respiratory Medicine, Zhongshan Hospital, Fudan University, Shanghai 200032, China.
authors.forename: Bi-jie
authors.initials: BJ
authors.lastname: Hu
authors.forename: Li
authors.initials: L
authors.lastname: Wei
authors.forename: Xiu-zhen
authors.initials: XZ
authors.lastname: Zhang
authors.forename: Ying-chun
authors.initials: YC
authors.lastname: Tang
authors.forename: Yu-xing
authors.initials: YX
authors.lastname: Ni
authors.forename: Yi-min
authors.initials: YM
authors.lastname: Li
authors.forename: Ji-quan
authors.initials: JQ
authors.lastname: Guo
authors.forename: Yun-jian
authors.initials: YJ
authors.lastname: Hu
authors.forename: Kou-xing
authors.initials: KX
authors.lastname: Zhang
authors.forename: Li
authors.initials: L
authors.lastname: Yang
mesh_terms: D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002443:Ceftriaxone / Q000494:pharmacology*; D015331:Cohort Studies; D003428:Cross Infection / Q000382:microbiology*; D024881:Drug Resistance, Bacterial; D005260:Female; D006801:Humans; D007709:Klebsiella / Q000187:drug effects; D007902:Length of Stay; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D018410:Pneumonia, Bacterial / Q000188:drug therapy / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects; D012189:Retrospective Studies; D013211:Staphylococcus aureus / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D002443:Ceftriaxone