title: Lessons from a one-year hospital-based surveillance of acute respiratory infections in Berlin- comparing case definitions to monitor influenza.
abstract: BACKGROUND
  Surveillance of severe acute respiratory infections (SARI) in sentinel hospitals is recommended to estimate the burden of severe influenza-cases. Therefore, we monitored patients admitted with respiratory infections (RI) in 9 Berlin hospitals from 7.12.2009 to 12.12.2010 according to different case definitions (CD) and determined the proportion of cases with influenza A(H1N1)pdm09 (pH1N1). We compared the sensitivity and specificity of CD for capturing pandemic pH1N1 cases.
  
  
  METHODS
  We established an RI-surveillance restricted to adults aged ≤ 65 years within the framework of a pH1N1 vaccine effectiveness study, which required active identification of RI-cases. The hospital information-system was screened daily for newly admitted RI-patients. Nasopharyngeal swabs from consenting patients were tested by PCR for influenza-virus subtypes. Four clinical CD were compared in terms of capturing pH1N1-positives among hospitalized RI-patients by applying sensitivity and specificity analyses. The broadest case definition (CD1) was used for inclusion of RI-cases; the narrowest case definition (CD4) was identical to the SARI case definition recommended by ECDC/WHO.
  
  
  RESULTS
  Over the study period, we identified 1,025 RI-cases, of which 283 (28%) met the ECDC/WHO SARI case definition. The percentage of SARI-cases among internal medicine admissions decreased from 3.2% (calendar-week 50-2009) to 0.2% (week 25-2010). Of 354 patients tested by PCR, 20 (6%) were pH1N1-positive. Two case definitions narrower than CD1 but -in contrast to SARI- not requiring shortness of breath yielded the largest areas under the Receiver-Operator-Curve. Heterogeneity of proportions of patients admitted with RI between hospitals was significant.
  
  
  CONCLUSIONS
  Comprehensive surveillance of RI cases was feasible in a network of community hospitals. In most settings, several hospitals should be included to ensure representativeness. Although misclassification resulting from failure to obtain symptoms in the hospital information-system cannot be ruled out, a high proportion of hospitalized PCR-positive pH1N1-patients (45%) did not fulfil the SARI case-definition that included shortness of breath or difficulty breathing. Thus, to assess influenza-related disease burden in hospitals, broader, alternative case definitions should be considered.
authors.affiliation: Department of Infectious Disease Epidemiology, Robert Koch Institute, DGZ-Ring 1, Berlin 13086, Germany. nachtnebel@post.harvard.edu
authors.forename: Matthias
authors.initials: M
authors.lastname: Nachtnebel
authors.forename: Benedikt
authors.initials: B
authors.lastname: Greutelaers
authors.forename: Gerhard
authors.initials: G
authors.lastname: Falkenhorst
authors.forename: Pernille
authors.initials: P
authors.lastname: Jorgensen
authors.forename: Manuel
authors.initials: M
authors.lastname: Dehnert
authors.forename: Brunhilde
authors.initials: B
authors.lastname: Schweiger
authors.forename: Christian
authors.initials: C
authors.lastname: Träder
authors.forename: Silke
authors.initials: S
authors.lastname: Buda
authors.forename: Tim
authors.initials: T
authors.lastname: Eckmanns
authors.forename: Ole
authors.initials: O
authors.lastname: Wichmann
authors.forename: Wiebke
authors.initials: W
authors.lastname: Hellenbrand
mesh_terms: D000293:Adolescent; D000328:Adult; D019540:Area Under Curve; D001604:Berlin / Q000453:epidemiology; D016001:Confidence Intervals; D005260:Female; D006751:Hospital Information Systems; D006760:Hospitalization / Q000706:statistics & numerical data*; D006764:Hospitals, Community; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification; D007252:Influenza Vaccines / Q000008:administration & dosage; D007251:Influenza, Human / Q000175:diagnosis* / Q000453:epidemiology* / Q000821:virology; D007362:Intensive Care Units / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D009305:Nasopharynx / Q000821:virology; D017063:Outcome Assessment, Health Care; D010343:Patient Admission / Q000706:statistics & numerical data* / Q000639:trends; D016133:Polymerase Chain Reaction; D012372:ROC Curve; D012141:Respiratory Tract Infections / Q000175:diagnosis / Q000453:epidemiology* / Q000821:virology; D018571:Sentinel Surveillance
chemical_list: D007252:Influenza Vaccines