Inpatient hospital fatality related to coding (ICD-9-CM) of the influenza diagnosis in Spain (2009-2015)

The Hospital Burden of Flu in Italy: a retrospective study on administrative data from season 2014-2015 to 2018-2019

BACKGROUND

Every year in Italy, influenza affects about 4 million people. Almost 5% of them are hospitalised. During peak illness, enormous pressure is placed on healthcare and economic systems. This study aims to quantify the clinical and economic burden of severe influenza during 5 epidemic seasons (2014-2019) from administrative claims data.

METHODS

Patients hospitalized with a diagnosis of influenza between October 2014, and April 2019, were analyzed. Clinical characteristics and administrative information were retrieved from health-related Administrative Databases (ADs) of 4 Italian Local Health Units (LHUs). The date of first admission was set as the Index Date (ID). A follow-up period of six months after ID was considered to account for complications and re-hospitalizations, while a lookback period (2 years before ID) was set to assess the prevalence of underlying comorbidities.

RESULTS

Out of 2,333 patients with severe influenza, 44.1% were adults ≥ 65, and 25.6% young individuals aged 0-17. 46.8% had comorbidities (i.e., were at risk), mainly cardiovascular and metabolic diseases (45.3%), and chronic conditions (24.7%). The highest hospitalization rates were among the elderly (≥ 75) and the young individuals (0-17), and were 37.6 and 19.5/100,000 inhabitants/year, respectively. The average hospital stay was 8 days (IQR: 14 - 4). It was higher for older individuals (≥ 65 years, 11 days, [17 - 6]) and for those with comorbidities (9 days, [16 - 6]), p-value < 0.001. Similarly, mortality was higher in elderly and those at risk (p-value < 0.001). Respiratory complications occurred in 12.7% of patients, and cardiovascular disorders in 5.9%. Total influenza-related costs were €9.7 million with hospitalization accounting for 95% of them. 47.3% of hospitalization costs were associated with individuals ≥ 65 and 52.9% with patients at risk. The average hospitalisation cost per patient was € 4,007.

CONCLUSIONS

This retrospective study showed that during the 2014-2019 influenza seasons in Italy, individuals of extreme ages and those with pre-existing medical conditions, were more likely to be hospitalized with severe influenza. Together with complications and ageing, they worsen patient's outcome and may lead to a prolonged hospitalization, thus increasing healthcare utilization and costs. Our data generate real-world evidence on the burden of influenza, useful to inform public health decision-making.

Impact of influenza related hospitalization in Spain: characteristics and risk factor of mortality during five influenza seasons (2016 to 2021)

Background

Estimating the global influenza burden in terms of hospitalization and death is important for optimizing prevention policies. Identifying risk factors for mortality allows for the design of strategies tailored to groups at the highest risk. This study aims to (a) describe the clinical characteristics of hospitalizations with a diagnosis of influenza over five flu seasons (2016-2017 to 2020-2021), (b) assess the associated morbidity (hospitalization rates and ICU admissions rate), mortality and cost of influenza hospitalizations in different age groups and (c) analyze the risk factors for mortality.

Methods

This retrospective study included all hospital admissions with a diagnosis of influenza in Spain for five influenza seasons. Data were extracted from the Spanish National Surveillance System for Hospital Data from 1 July 2016 to 30 June 2021. We identified cases coded as having influenza as a primary or secondary diagnosis (International Classification of Diseases, 10th revision, J09-J11). The hospitalization rate was calculated relative to the general population. Independent predictors of mortality were identified using multivariable logistic regression.

Results

Over the five seasons, there were 127,160 hospitalizations with a diagnosis of influenza. The mean influenza hospitalization rate varied from 5/100,000 in 2020-2021 (COVID-19 pandemic) to 92.9/100,000 in 2017-2018. The proportion of influenza hospitalizations with ICU admission was 7.4% and was highest in people aged 40-59 years (13.9%). The case fatality rate was 5.8% overall and 9.4% in those aged 80 years or older. Median length of stay was 5 days (and 6 days in the oldest age group). In the multivariable analysis, independent risk factors for mortality were male sex (odds ratio [OR] 1.14, 95% confidence interval [95% CI] 1.08-1.20), age (<5 years: OR 1; 5-19 years: OR 2.02, 95%CI 1.17-3.49; 20-39 years: OR 4.11, 95% CI 2.67-6.32; 40-59 years: OR 8.15, 95% CI 5.60-11.87; 60-79 years: OR 15.10, 95% CI 10.44-21.84; ≥80 years: OR 33.41, 95% CI 23.10-48.34), neurological disorder (OR 1.97, 95% CI 1.83-2.11), heart failure (OR 1.85, 95% CI 1.74-1.96), chronic kidney disease (OR 1.33, 95% CI 1.25-1.41), chronic liver disease (OR 2.95, 95% CI 2.68-3.27), cancer (OR 1.85, 95% CI 1.48-2.24), coinfection with SARS-CoV2 (OR 3.17, 95% CI 2.34-4.28), influenza pneumonia (OR 1.76, 95% CI 1.66-1.86) and admission to intensive care (OR 7.81, 95% CI 7.31-8.36).

Conclusion

Influenza entails a major public health burden. People aged over 60-and especially those over 80-show the longest hospital stays. Age is also the most significant risk factor for mortality, along with certain associated comorbidities.

Influenza hospitalisations in Spain between the last influenza and COVID-19 pandemic (2009-2019)

Knowing the burden of severe disease caused by influenza is essential for disease risk communication, to understand the true impact of vaccination programmes and to guide public health and disease control measures. We estimated the number of influenza-attributable hospitalisations in Spain during the 2010-2011 to 2019-2020 seasons - based on the hospitalisations due to severe acute respiratory infection (SARI) in Spain using the hospital discharge database and virological influenza information from the Spanish Influenza Sentinel Surveillance System (SISSS). The weekly numbers of influenza-attributable hospitalisations were calculated by multiplying the weekly SARI hospitalisations by the weekly influenza virus positivity, obtained from the SISSS in each season, stratified by age group and sex. The influenza-related hospitalisation burden is age-specific and varies significantly by influenza season. People aged 65 and over yielded the highest average influenza-attributable hospitalisation rates per season (615.6 per 100,000), followed by children aged under 5 (251.2 per 100,000). These results provide an essential contribution to influenza control and to improving existing vaccination programmes, as well as to the optimisation and planning of health resources and policies.

Understanding the Global Burden of Influenza in Adults Aged 18-64 years: A Systematic Literature Review from 2012 to 2022

INTRODUCTION

Adults aged 18-64 years comprise most of the working population, meaning that influenza infection can be disruptive, causing prolonged absence from the workplace, and reduced productivity and the ability to care for dependents. Influenza vaccine uptake is relatively low, even among the older adults in this population (i.e., aged 50-64 years), reflecting a lack of perceived need for vaccination. This systematic literature review (SLR) aimed to characterize the global burden of influenza in the 18-64 years population.

METHODS

An electronic database search was conducted and supplemented with conference and gray literature searches. Eligible studies described at least one of clinical, humanistic, or economic outcomes in adults aged 18-64 years and conducted across several global regions. Included studies were published in English, between January 1, 2012, and September 20, 2022.

RESULTS

A total of 40 publications were included, with clinical, humanistic, and economic outcomes reported in 39, 5, and 15, respectively. Risk of influenza-associated clinical outcomes were reported to increase with age among the 18-64 years population, including hospitalizations (Yamana et al. in Intern Med 60:3401-3408, 2021; Derqui et al. in Influenza Other Respir Viruses 16:862-872, 2022; Fuller et al. in Influenza Other Respir Viruses 16:265-275, 2022; Ortiz et al. in Crit Care Med 42:2325-2332, 2014; Yandrapalli et al. in Ann Transl Med 6:318, 2018; Zimmerman et al. in Influenza Other Respir Viruses 16:1133-1140, 2022). ICU admissions, mortality, ER/outpatient visits, and use of mechanical ventilation were recorded. Adults aged 18-64 years with underlying comorbidities were at higher risk of influenza-related hospitalizations, ICU admission, and mortality than otherwise healthy individuals. Length of hospital stay increased with age, although a lack of stratification across other economic outcomes prevented identification of further trends across age groups.

CONCLUSIONS

High levels of hospitalization and outpatient visits demonstrated a clinical influenza-associated burden on patients and healthcare systems, which is exacerbated by comorbidities. Considering the size and breadth of the general population aged 18-64 years, the limited humanistic and economic findings of this SLR likely reflect an underreported burden. Greater investigation into indirect costs and prolonged absenteeism associated with influenza infection is required to fully understand the economic burden in this population.

Estimating the contribution of respiratory pathogens to acute exacerbations of COPD using routine data

OBJECTIVES

To characterise microbiology testing and results associated with emergency admissions for acute exacerbation of COPD (AECOPD), and determine the accuracy of ICD-10 codes in retrospectively identifying laboratory-confirmed respiratory pathogens in this setting.

METHODS

Using person-level data from the Secure Anonymised Information Linkage Databank in Wales, we extracted emergency admissions for COPD from 1/12/2016 to 30/11/2018 and undertook linkage of admissions data to microbiology data to identify laboratory-confirmed infection. We further used these data to assess the accuracy of pathogen-specific ICD-10 codes.

RESULTS

We analysed data from 15,950 people who had 25,715 emergency admissions for COPD over the two-year period. 99.5% of admissions could be linked to a laboratory test within 7 days of admission date. Sputum was collected in 5,013 (19.5%) of admissions, and respiratory virus testing in 1,219 (4.7%). Where respiratory virus testing was undertaken, 46.7% returned any positive result. Influenza was the virus most frequently detected, in 21.5% of admissions where testing was conducted. ICD-10 codes exhibited low sensitivity in detecting laboratory-confirmed respiratory pathogens.

CONCLUSIONS

In people admitted to hospital with AECOPD, increased testing for respiratory viruses could enable more effective antibiotic stewardship and isolation of cases. Linkage with microbiology data achieves more accurate and reliable case definitions.

Excess hospitalizations and mortality associated with seasonal influenza in Spain, 2008-2018

BACKGROUND

Influenza may trigger complications, particularly in at-risk groups, potentially leading to hospitalization or death. However, due to lack of routine testing, influenza cases are infrequently coded with influenza-specific diagnosis. Statistical models using influenza activity as an explanatory variable can be used to estimate annual hospitalizations and deaths associated with influenza. Our study aimed to estimate the clinical and economic burden of severe influenza in Spain, considering such models.

METHODS

The study comprised ten epidemic seasons (2008/2009-2017/2018) and used two approaches: (i) a direct method of estimating the seasonal influenza hospitalization, based on the number of National Health Service hospitalizations with influenza-specific International Classification of Diseases (ICD) codes (ICD-9: 487-488; ICD-10: J09-J11), as primary or secondary diagnosis; (ii) an indirect method of estimating excess hospitalizations and deaths using broader groups of ICD codes in time-series models, computed for six age groups and four groups of diagnoses: pneumonia or influenza (ICD-9: 480-488, 517.1; ICD-10: J09-J18), respiratory (ICD-9: 460-519; ICD-10: J00-J99), respiratory or cardiovascular (C&R, ICD-9: 390-459, 460-519; ICD-10: I00-I99, J00-J99), and all-cause. Means, excluding the H1N1pdm09 pandemic (2009/2010), are reported in this study.

RESULTS

The mean number of hospitalizations with a diagnosis of influenza per season was 13,063, corresponding to 28.1 cases per 100,000 people. The mean direct annual cost of these hospitalizations was €45.7 million, of which 65.7% was generated by patients with comorbidities. Mean annual influenza-associated C&R hospitalizations were estimated at 34,894 (min: 16,546; max: 52,861), corresponding to 75.0 cases per 100,000 (95% confidence interval [CI]: 63.3-86.3) for all ages and 335.3 (95% CI: 293.2-377.5) in patients aged ≥ 65 years. We estimate 3.8 influenza-associated excess C&R hospitalizations for each hospitalization coded with an influenza-specific diagnosis in patients aged ≥ 65 years. The mean direct annual cost of the estimated excess C&R hospitalizations was €142.9 million for all ages and €115.9 million for patients aged ≥ 65 years. Mean annual influenza-associated all-cause mortality per 100,000 people was estimated at 27.7 for all ages.

CONCLUSIONS

Results suggest a relevant under-detected burden of influenza mostly in the elderly population, but not neglectable in younger people.

Clinical and economic burden of physician-diagnosed influenza in adults during the 2017/2018 epidemic season in Spain

BACKGROUND

Influenza is an acutely debilitating respiratory infection, contributing significantly to outpatient visits and hospitalizations. Spain lacks comprehensive and updated data on the burden of influenza, particularly in the outpatient setting. Our study aimed to fill this gap by estimating the clinical and economic burden of physician-diagnosed influenza cases in adults from four Spanish regions, stratified by age groups and presence of comorbidities.

METHODS

A retrospective cost-of-illness study was conducted using data from an electronic medical records database from the National Healthcare Service (NHS) of four Spanish regions for individuals aged ≥ 18 years diagnosed for influenza during the 2017/2018 epidemic season. Health resource utilization and related cost data were collected, including primary care visits, referrals to other specialists, visits to the emergency department, hospitalizations, and prescribed medicines.

RESULTS

The study reported a total of 28,381 patients aged ≥ 18 years diagnosed with influenza, corresponding to 1,804 cases per 100,000 population. Most patients were aged < 65 years: 60.5% (n = 17,166) aged 18-49 and 26.3% (n = 7,451) 50-64 years. A total of 39.2% (n = 11,132) of patients presented a comorbidity. Cardiovascular diseases were the most common comorbidity reported along with influenza. The mean healthcare cost per case was estimated at €235.1 in population aged 18-49 years, increasing by 1.7 and 4.9 times in those aged 50-64 (€402.0) and ≥ 65 (€1,149.0), respectively. The mean healthcare cost per case was 3.2 times higher in patients with comorbidities. The total healthcare cost of medically attended influenza cases was mainly driven by primary care (45.1%) and hospitalization (42.0%). Patients aged 18-64 years old accounted for 61.9% of the costs of medically attended influenza. Irrespective of age, patients with comorbidities accounted for 67.1% of costs.

CONCLUSIONS

Season 2017/2018 was associated with a considerable burden of influenza in Spain, which increased with age and presence of comorbidities. Individuals with comorbidities accounted for most of the costs of influenza. Results suggest that population aged 18-64 years old is generating the highest share of costs to the NHS when all healthcare costs are considered. Preventive strategies targeting subjects with comorbidities, regardless of age, should be warranted.

Hospital admissions with influenza and impact of age and comorbidities on severe clinical outcomes in Brazil and Mexico

Background

The risk of hospitalization or death after influenza infection is higher at the extremes of age and in individuals with comorbidities. We estimated the number of hospitalizations with influenza and characterized the cumulative risk of comorbidities and age on severe outcomes in Mexico and Brazil.

Methods

We used national hospital discharge data from Brazil (SIH/SUS) from 2010–2018 and Mexico (SAEH) from 2010–2017 to estimate the number of influenza admissions using ICD-10 discharge codes, stratified by age (0–4, 5–17, 18–49, 50–64, and ≥65 years). Duration of hospital stay, admission to the intensive care unit (ICU), and in-hospital case fatality rates (CFRs) defined the severe outcomes. Rates were compared between patients with or without pre-specified comorbidities and by age.

Results

A total of 327,572 admissions with influenza were recorded in Brazil and 20,613 in Mexico, with peaks period most years. In Brazil, the median hospital stay duration was 3.0 days (interquartile range, 2.0–5.0), ICU admission rate was 3.3% (95% CI, 3.2–3.3%), and in-hospital CFR was 4.6% (95% CI, 4.5–4.7). In Mexico, the median duration of stay was 5.0 days (interquartile range, 3.0–7.0), ICU admission rate was 1.8% (95% CI, 1.6–2.0%), and in-hospital CFR was 6.9% (95% CI, 6.5–7.2). In Brazil, ICU admission and in-hospital CFR were higher in adults aged ≥50 years and increased in the presence of comorbidities, especially cardiovascular disease. In Mexico, comorbidities increased the risk of ICU admission by 1.9 (95% CI, 1.0–3.5) and in-hospital CFR by 13.9 (95% CI, 8.4–22.9) in children 0–4 years.

Conclusion

The SIH/SUS and SAEH databases can be used to estimate hospital admissions with influenza, and the disease severity. Age and comorbidities, especially cardiovascular disease, are cumulatively associated with more severe outcomes, with differences between countries. This association should be further analyzed in prospective surveillance studies designed to support influenza vaccination strategy decisions.

Circulation of influenza A viruses among patients hospitalized for severe acute respiratory infection in a tertiary care hospital in Romania in the 2018/19 season: Results from an observational descriptive epidemiological study

The seasonal circulation of influenza viruses and the impact that this infection has on the population varies from year to year. We have prospectively captured hospital-based surveillance data describing the circulation of influenza viruses and characterizing patients with influenza admitted to a tertiary hospital in Bucharest, Romania in the 2018/19 season.We have conducted an observational descriptive epidemiological study analyzing all consecutive patients hospitalized for influenza like illness or severe acute respiratory infection at the National Institute for Infectious Diseases "Prof. Dr. Matei Balş", Bucharest, Romania, from November 2018 to April 2019. For all patients we actively collected standardized clinical information and performed real-time reverse transcription polymerase chain reaction testing of respiratory samples to identify the presence of influenza viruses and to determine the subtype/lineage.A total of 1128 hospitalized patients were tested in this study, with an influenza positivity rate of 41.2% (n = 465). We identified an exclusive circulation of influenza A viruses (A/H1 - 57.2%, A/H3 - 29.3%, A not subtyped - 13.3%), with only 1 case of influenza B detected at the end of the season (week 18/2019). Children under 5 years of age accounted for the majority of cases (40%, n = 186), and all cases had a favorable evolution. Females were more likely to test positive for influenza (53.3%) compared to males (46.7%), P = .048, and presence of asthma or chronic obstructive pulmonary disease increased the risk of influenza 4.4-fold and 2-fold, respectively (P < .001 and P = .034). Thirteen influenza patients required hospitalization in intensive care and 5 deaths were recorded (1.1%). The vaccination rate for all patients included in the study was low (4.6%). The existence of chronic conditions or age over 65 years prolonged the hospitalization period with 2 days (P < .001 each).In the 2018/19 season, we identified an important circulation of influenza A viruses among patients hospitalized for influenza like illness/severe acute respiratory infection in a tertiary care hospital in Romania, with a higher likelihood of affecting females and patients with pre-existing lung conditions. Monitoring of the clinical and epidemiological characteristics of influenza virus infection is of great interest and should be done carefully each season to better inform on the necessary measures to limit the impact that this infection may have on risk groups.