Research Article: Characteristics and outcomes of a cohort hospitalized for pandemic and seasonal influenza in Germany based on nationwide inpatient data

Date Published: July 14, 2017

Publisher: Public Library of Science

Author(s): Daniel von der Beck, Werner Seeger, Susanne Herold, Andreas Günther, Benjamin Löh, Chih-Jung Chen.


From June of 2009 to August of 2010 the influenza subtype H1N1pdm09 caused a worldwide pandemic. The impact on populations and health care systems around the globe evolved differently. Substantial data come from the German national surveillance network in an outpatient and private practice setting, while information on hospitalized patients in Germany is rather limited.

Data from the Federal Statistics Office comprising health insurance claims of the entire nationwide inpatient sample from 2005 to 2012 were used to identify patients who were hospitalized for laboratory-confirmed influenza and to analyse demographical aspects, comorbidities, hospitalization duration, outcomes and ventilator use during the pandemic and seasonal waves of influenza.

A number of 34,493 admissions for laboratory-confirmed influenza occurred during waves between 2005 and 2012. During the pandemic seasonal waves, the number of hospitalizations vastly surpassed the level that was seen in any of the seasonal waves. A major demographic shift was seen with respect to patient age, as younger patients (< 60 years old) were more frequently hospitalized. Mean length of stay was shorter (149 vs. 193 hours), mean time on ventilation tended to be shorter (261 vs. 305 hours) in young children (< 4 years old) and longer (393 vs. 339 hours) in the elderly (> 60 years old). Time to ventilation was shorter in non-fatal cases (328 vs. 349 hours) and longer in fatal cases (419 vs. 358 hours). Logistic regression was used to show the impact of comorbidities and co-diagnoses on mortality and the need for ventilation, as well as differences between pandemic and seasonal influenza.

Inpatient data suggest differences in patient populations during pandemic and seasonal influenza. Younger patients were more frequently hospitalized. Differences with respect to the presence of certain comorbidities and co-diagnoses, length of stay, time to ventilation and ventilation time could be identified.

Partial Text

Influenza is a viral infectious disease that appears as yearly seasonal epidemics of varying severity[1]. Clinically-relevant morbidity is caused by virus types A and B. Influenza A is further subtyped according to the haemagglutinin (H) and neuraminidase (N) antigens[1]. Influenza has major impact on healthcare systems and economies around the globe[1]. Pandemic waves, i.e., rapid worldwide spreads among large populations, were observed in 1918–1920 (‘Spanish flu’, A/H1N1), 1957 (‘Asian flu’), 1968 (‘Hong Kong flu’), 1977/78 (‘Russian flu’, A/H1N1) with the most recent pandemic occurring in 2009 (‘swine flu’, A/H1N1)[2]. Due to the wide spread of the disease during pandemic waves, a significantly greater morbidity and a higher death toll can be attributed to influenza pandemics as compared to seasonal occurrences of influenza[2]. The first cases of the 2009 pandemic were detected in the Mexican federal district of Mexico City on 18th March, 2009[3–5]. Cases were reported in the southern region of the United States of America by the end of March[6]. The highest infectious counts of H1N1 in different countries occurred non-contemporaneously around the globe, with peak numbers in Germany in November[7].

The G-DRG data suggest that the 2009/10 pandemic influenza has distinct characteristics when compared to seasonal influenza waves. The study allows for the identification of comorbidities and co-diagnoses that are more frequently associated either with pandemic or seasonal influenza, and can identify their impact on outcomes such as in-hospital mortality and the need for mechanical ventilation. Based upon statutory reports, Buda et al. reported a number of n = 7,882 influenza hospitalizations from the 18th week of 2009 until the 17th week of 2010. This is a considerably lower count than estimated from the G-DRG database (Fig 1, Table 1). Obvious differences with respect to the data sources can be explained by the legal requirement to report an influenza case (or suspicion of one) and the G-DRG coding of cases for the purpose of health insurance claims. In general, the number of reported cases is considered an underestimation of the actual count, and strongly depends on the legal and medical infrastructure of the reporting country. The G-DRG database represents a retrospective cohort and data monitoring is not performed as in prospective cohorts. Nonetheless, data quality is ensured since diagnosis and coding quality is monitored by the professional medical service to the statutory health insurance, which reviews roughly 10% of all insurance claims[29]. Thus, the G-DRG data indicate that the burden of influenza-related hospitalization in Germany may be higher than estimated by the data from the statutory reporting system alone.




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