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Lessons from a one-year hospital-based surveillance of acute respiratory infections in Berlin- comparing case definitions to monitor influenza.

Nachtnebel M, Greutelaers B, Falkenhorst G, Jorgensen P, Dehnert M, Schweiger B, Träder C, Buda S, Eckmanns T, Wichmann O, Hellenbrand W - BMC Public Health (2012)

Bottom Line: 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.Heterogeneity of proportions of patients admitted with RI between hospitals was significant.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.

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Affiliation: Department of Infectious Disease Epidemiology, Robert Koch Institute, DGZ-Ring 1, Berlin 13086, Germany. nachtnebel@post.harvard.edu

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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Incidence of respiratory infections fulfilling criteria for CD1 admitted to intensive care units (ICU) as a percentage of all admissions to ICU per calendar week. Weekly incidences are shown together with predicted incidences and 95%CI according to Poisson regression. All pH1N1 cases notified in Berlin through the national routine surveillance system, 2009-2010 are shown for comparison.
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Figure 3: Incidence of respiratory infections fulfilling criteria for CD1 admitted to intensive care units (ICU) as a percentage of all admissions to ICU per calendar week. Weekly incidences are shown together with predicted incidences and 95%CI according to Poisson regression. All pH1N1 cases notified in Berlin through the national routine surveillance system, 2009-2010 are shown for comparison.

Mentions: We calculated the weekly incidence of all CD1-cases, CD1b cases, and CD4 cases as a percentage of all admissions to internal medicine wards and of all CD1-cases admitted to ICU as a percentage of all ICU admissions (Figure 2 and 3, Table 3). All incidences showed statistically significant changes over time. Admission of CD1b cases exhibited a biphasic pattern with a decline from 5.1% in week 50/2009 to a minimum of 1.4% in week 29/2010, with a weekly IRR of 0.99 (95%CI: 0.98-1.00). Thereafter, the IRR was 1.02 (95%CI: 1.00-1.03) per week until the end of the study period with a maximum of 5.6% in week 41 in 2010. We observed a similar pattern for CD4 cases with an IRR of 0.96 (95%CI: 0.94-0.98) per week to a minimum of 0.2% in week 25 in 2010; followed by a weekly IRR of 1.03 (95%CI: 1.00-1.06). In contrast, the incidence of all cases among ICU admissions decreased over the entire study period with an IRR of 0.98 per week (95%CI: 0.97-0.99).


Lessons from a one-year hospital-based surveillance of acute respiratory infections in Berlin- comparing case definitions to monitor influenza.

Nachtnebel M, Greutelaers B, Falkenhorst G, Jorgensen P, Dehnert M, Schweiger B, Träder C, Buda S, Eckmanns T, Wichmann O, Hellenbrand W - BMC Public Health (2012)

Incidence of respiratory infections fulfilling criteria for CD1 admitted to intensive care units (ICU) as a percentage of all admissions to ICU per calendar week. Weekly incidences are shown together with predicted incidences and 95%CI according to Poisson regression. All pH1N1 cases notified in Berlin through the national routine surveillance system, 2009-2010 are shown for comparison.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3362781&req=5

Figure 3: Incidence of respiratory infections fulfilling criteria for CD1 admitted to intensive care units (ICU) as a percentage of all admissions to ICU per calendar week. Weekly incidences are shown together with predicted incidences and 95%CI according to Poisson regression. All pH1N1 cases notified in Berlin through the national routine surveillance system, 2009-2010 are shown for comparison.
Mentions: We calculated the weekly incidence of all CD1-cases, CD1b cases, and CD4 cases as a percentage of all admissions to internal medicine wards and of all CD1-cases admitted to ICU as a percentage of all ICU admissions (Figure 2 and 3, Table 3). All incidences showed statistically significant changes over time. Admission of CD1b cases exhibited a biphasic pattern with a decline from 5.1% in week 50/2009 to a minimum of 1.4% in week 29/2010, with a weekly IRR of 0.99 (95%CI: 0.98-1.00). Thereafter, the IRR was 1.02 (95%CI: 1.00-1.03) per week until the end of the study period with a maximum of 5.6% in week 41 in 2010. We observed a similar pattern for CD4 cases with an IRR of 0.96 (95%CI: 0.94-0.98) per week to a minimum of 0.2% in week 25 in 2010; followed by a weekly IRR of 1.03 (95%CI: 1.00-1.06). In contrast, the incidence of all cases among ICU admissions decreased over the entire study period with an IRR of 0.98 per week (95%CI: 0.97-0.99).

Bottom Line: 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.Heterogeneity of proportions of patients admitted with RI between hospitals was significant.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Infectious Disease Epidemiology, Robert Koch Institute, DGZ-Ring 1, Berlin 13086, Germany. nachtnebel@post.harvard.edu

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.

Show MeSH
Related in: MedlinePlus