Lessons from a one-year hospital-based surveillance of acute respiratory infections in Berlin- comparing case definitions to monitor influenza
Creators: name: Nachtnebel, Matthias
name: Greutélaers, Benedikt
name: Falkenhorst, Gerhard
name: Jorgensen, Pernille
name: Dehnert, Manuel
name: Schweiger, Brunhilde
name: Träder, Christian
name: Buda, Silke
name: Eckmanns, Tim
name: Wichmann, Ole
name: Hellenbrand, Wiebke
Publisher: name: Robert Koch-Institut, Infektionsepidemiologie
Year: 2012
Subjects: subject: Adolescent
subject: Humans
subject: Female
subject: Polymerase Chain Reaction
subject: Male
subject: Middle Aged
subject: Adult
subject: Sentinel Surveillance
subject: Influenza A Virus
subject: Respiratory Tract Infections/epidemiology
subject: Respiratory Tract Infections/virology
subject: Berlin/epidemiology
subject: H1N1 Subtype/isolation &amp; purification
subject: Hospitalization/statistics &amp; numerical data
subject: Influenza Human/virology
subject: Nasopharynx/virology
subject: Influenza Human/epidemiology
subject: Influenza Human/diagnosis
subject: Intensive Care Units/statistics &amp; numerical data
subject: Influenza Vaccines/administration &amp; dosage
subject: Area Under Curve
subject: Confidence Intervals
subject: Hospital Information Systems
subject: Hospitals Community
subject: Outcome Assessment (Health Care)
subject: Patient Admission/statistics &amp; numerical data
subject: Patient Admission/trends
subject: ROC Curve
subject: Respiratory Tract Infections/diagnosis
subject: 610 Medizin

description: 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.