The elderly and persons with specific chronic conditions are known to face elevated morbidity and mortality risks resulting from an influenza infection, and hence are routinely recommended for annual influenza vaccination. However, risk-specific mortality rates have not been established. We estimated age-specific influenza-attributable mortality rates stratified by the presence of chronic conditions and type of residence based on deaths of persons who were admitted to hospital with a respiratory complication captured in our national database. The majority of patients had chronic heart or respiratory conditions (80%) and were admitted from the community (80%). Influenza-attributable mortality rates clearly increase with age for all risk groups. Our influenza-specific estimates identified higher risk ratios for chronic lung or heart disease than have been suggested by other methods. These estimates identify groups most in need of improved vaccines and for whom the use of additional strategies, such as immunization of household contacts or caregivers should be considered.
Uncertainty regarding the benefits of influenza vaccination may contribute to the underutilization of this vaccine. We have conducted serial cohort studies using the administrative data bases of a Twin Cities based managed care organization to assess the impact of disease and benefits of vaccination among the elderly. For the 6 seasons 1990-1991 through 1995-1996, there were more than 20,000 elderly members of the health plan included in each cohort. Data collected included information on baseline demographic and health characteristics, vaccination status and outcomes (hospitalizations and death). Multivariate regression techniques were used to compare the risks of outcomes between vaccinated and unvaccinated persons while controlling for covariates and confounders. Results for data pooled over the 6 seasons demonstrated that influenza vaccination was associated with significant reductions in hospitalizations, outpatient visits, and death among the elderly. Similar findings were observed for low, intermediate, and high risk subgroups. Vaccination was also associated with cost savings. These findings are consistent with results from studies conducted in other countries and over other seasons and strongly support age-based recommendations for annual influenza vaccination for all persons ages 65 and over.
The aim of this study was to investigate the incidence of influenza-related encephalitis in Sweden during 11.5 years. Studies from Japan report an increased incidence of influenza-related encephalitis/encephalopathy. Few other studies are available. We conducted a retrospective register-based study on the Swedish National Inpatient Register, which covers all Swedish hospitals. In 1987-1998, a total number of 14,250 hospitalized individuals had an influenza diagnosis (population incidence: 137 per million person-years). In-hospital mortality was 4.1%. Using three different approaches, only 21 cases of influenza-related encephalitis were found, corresponding to a rate of 1.5 per 1,000 hospitalized persons with an influenza diagnosis (population incidence 0.21 per million person-years). We conclude that encephalitis following influenza occurs rarely, or is an infrequently recognized, diagnosed or reported complication. The cases we studied in detail have all recovered without sequels.
The results of the study of the autopsy materials from 61 patients with the diagnosis of pneumonia received by virological and genetic methods are reviewed. The materials were studied at the Influenza Etiology and Epidemiology Center of the Ivanovsky Institute of Virology, Ministry of Health and Social Development of the Russian Federation, during epidemic seasons 2009-2010 and 2010-2011. The data were analyzed with respect to age, sex, comorbidity diseases and identified on the groups of the risk of severe forms of the disease. The presence of the pandemic influenza virus strain RNA was confirmed in 70.5% of materials; RNA of influenza B was detected in 1.2% cases. The co-infections caused by the bocavirus, adenovirus, parainfluenza virus type 2 and 4, rhinovirus, and streptococcus were detected only in 19.7%. In most cases, the influenza virus was the etiologic agent of lethal pneumonia, which justifies the necessity of the early etiological diagnosis and treatment with antiviral drugs.
Although the increased risk of hospitalization and mortality during influenza seasons has been documented extensively, there is a relative paucity of research on the impact of influenza-related illnesses on other health care use indicators, such as physician use. The purpose of this study was to examine the impact of influenza-associated respiratory illnesses on the Winnipeg health care system, including hospitalizations, physician visits and emergency room visits. Their impact on mortality was also examined.
Administrative data were used to track health care use and mortality over four influenza seasons (1995-96 to 1998-99). Excess health care use and deaths were calculated by subtracting rates during influenza seasons from those during weeks when influenza viruses were not circulating.
Significant excess hospitalization, physician visit, and emergency room visit rates emerged for influenza and pneumonia, acute respiratory diseases, and chronic lung disease, especially among children and adults aged 65 and over. Considerable excess mortality due to influenza and pneumonia and chronic lung disease among individuals aged 65 and over also emerged, particularly among nursing home residents.
Influenza-associated respiratory illnesses have a substantial impact on the health care system. Given the burden of illness among children during influenza seasons, the study further suggests that influenza vaccination might be considered for this age group.
