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BMC Public Health. 2012; 12: 245.
Published online Mar 27, 2012. doi:  10.1186/1471-2458-12-245
PMCID: PMC3362781
Lessons from a one-year hospital-based surveillance of acute respiratory infections in Berlin- comparing case definitions to monitor influenza
Matthias Nachtnebel,corresponding author1,2,3 Benedikt Greutelaers,1,2,3 Gerhard Falkenhorst,4 Pernille Jorgensen,4 Manuel Dehnert,1 Brunhilde Schweiger,5 Christian Träder,6 Silke Buda,7 Tim Eckmanns,8 Ole Wichmann,4 and Wiebke Hellenbrand4
1Department of Infectious Disease Epidemiology, Robert Koch Institute, DGZ-Ring 1, Berlin 13086, Germany
2Post Graduate Training in Applied Epidemiology, Robert Koch Institute, Berlin, Germany
3European Programme for Intervention Epidemiology Training (EPIET), European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden
4Immunization Unit, Robert Koch Institute, Berlin, Germany
5National Reference Centre for Influenza, Robert Koch Institute, Berlin, Germany
6Vivantes Clinic, Berlin, Germany
7Respiratory Disease Unit, Robert Koch Institute, Berlin, Germany
8Surveillance Unit, Robert Koch Institute, Berlin, Germany
corresponding authorCorresponding author.
Matthias Nachtnebel: nachtnebel/at/post.harvard.edu; Benedikt Greutelaers: greutelaersb/at/rki.de; Gerhard Falkenhorst: falkenhorstg/at/rki.de; Pernille Jorgensen: pernille.jorgensen/at/gmail.com; Manuel Dehnert: dehnertm/at/rki.de; Brunhilde Schweiger: schweigerb/at/rki.de; Christian Träder: christian.traeder/at/vivantes.de; Silke Buda: budas/at/rki.de; Tim Eckmanns: eckmannst/at/rki.de; Ole Wichmann: wichmanno/at/rki.de; Wiebke Hellenbrand: hellenbrandw/at/rki.de
Received September 12, 2011; Accepted March 27, 2012.
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.
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