Laboratory-confirmed Influenza Surveillance Research Articles

Economic burden of influenza illness among children under 5 years in Suzhou, China: Report from the cost surveys during 2011/12 to 2016/17 influenza seasons

BackgroundData are limited on the economic burden of seasonal influenza in China. We estimated the cost due to influenza illness among children < 5-year-old in Suzhou, China. MethodsThis study adopted a societal perspective to estimate direct medical cost, direct non-medical cost, and indirect cost related to lost productivity. Data to calculate costs and rates of three influenza illness outcomes (non-medically attended, outpatient and hospitalization) were collected from prospective community-based cohort studies and hospital-based enhanced laboratory-confirmed influenza surveillance in Suzhou during the 2011/12 to 2016/17 influenza seasons. We used mean cost-per-episode, annual incidence rates of episodes of each outcome, and annual population size to estimate the total annual economic burden of influenza illnesses among children < 5-year-old for Suzhou. All costs were reported in 2017 U.S. dollars. ResultsThe mean cost-per-episode (standard deviation) was $9.92 (13.26) for non-medically attended influenza, $161.05 (176.98) for influenza outpatient illnesses, and $1425.95 (603.59) for influenza hospitalizations. By applying the annual incidence rates to the population size, we estimated an annual total of 4,919 episodes of non-medically attended influenza, 21,994 influenza outpatient, and 2,633 influenza hospitalization. Total annual economic burden of influenza to society among children < 5-year-old in Suzhou was $7.37 (95% confidence interval, 6.9–7.8) million, with estimated costs for non-medically attended influenza of $49,000 (46,000–52,000), influenza outpatients $3.5 (3.3–3.8) million, and influenza hospitalizations $3.8 (3.6–3.9) million. Among outpatients, the indirect cost was 36.3% ($1.3 million) of total economic burden, accounting for 21,994 days of lost productivity annually. Among inpatients, the indirect cost was 22.1% ($829,000), accounting for 18,431 days of lost productivity annually. ConclusionsOur findings show that influenza in children < 5-year-oldcauses substantial societal economic burden in Suzhou, China. Assessing the potential economic benefit of increasing influenza vaccination coverage in this population is warranted.

Influenza economic burden among potential target risk groups for immunization in South Africa, 2013–2015

BackgroundData on influenza economic burden in risk groups for severe influenza are important to guide targeted influenza immunization, especially in resource-limited settings. However, this information is limited in low- and middle-income countries. MethodsWe estimated the cost (from a health system and societal perspective) and years of life lost (YLL) for influenza-associated illness in South Africa during 2013–2015 among (i) children aged 6–59 months, (ii) individuals aged 5–64 years with HIV, pulmonary tuberculosis (PTB) and selected underlying medical conditions (UMC), separately, (iii) pregnant women and (iv) individuals aged ≥65 years, using publicly available data and data collected through laboratory-confirmed influenza surveillance and costing studies. All costs were expressed in 2015 prices using the South Africa all-items Consumer Price Index. ResultsDuring 2013–2015, the mean annual cost of influenza-associated illness among the selected risk groups accounted for 52.1% ($140.9/$270.5 million) of the total influenza-associated illness cost (for the entire population of South Africa), 45.2% ($52.2/$115.5 million) of non-medically attended illness costs, 43.3% ($46.7/$107.9 million) of medically-attended mild illness costs and 89.3% ($42.0/$47.1 million) of medically-attended severe illness costs. The YLL among the selected risk groups accounted for 86.0% (262,069 /304,867 years) of the total YLL due to influenza-associated death. ConclusionIn South Africa, individuals in risk groups for severe influenza accounted for approximately half of the total influenza-associated illness cost but most of the cost of influenza-associated medically attended severe illness and YLL. This study provides the foundation for future studies on the cost-effectiveness of influenza immunization among risk groups.

Quantifying the annual incidence and underestimation of seasonal influenza: A modelling approach

BackgroundSeasonal influenza poses a significant public health and economic burden, associated with the outcome of infection and resulting complications. The true burden of the disease is difficult to capture due to the wide range of presentation, from asymptomatic cases to non-respiratory complications such as cardiovascular events, and its seasonal variability. An understanding of the magnitude of the true annual incidence of influenza is important to support prevention and control policy development and to evaluate the impact of preventative measures such as vaccination.MethodsWe use a dynamic disease transmission model, laboratory-confirmed influenza surveillance data, and randomized-controlled trial (RCT) data to quantify the underestimation factor, expansion factor, and symptomatic influenza illnesses in the US and Canada during the 2011-2012 and 2012-2013 influenza seasons.ResultsBased on 2 case definitions, we estimate between 0.42−3.2% and 0.33−1.2% of symptomatic influenza illnesses were laboratory-confirmed in Canada during the 2011-2012 and 2012-2013 seasons, respectively. In the US, we estimate between 0.08−0.61% and 0.07−0.33% of symptomatic influenza illnesses were laboratory-confirmed in the 2011-2012 and 2012-2013 seasons, respectively. We estimated the symptomatic influenza illnesses in Canada to be 0.32−2.4 million in 2011-2012 and 1.8−8.2 million in 2012-2013. In the US, we estimate the number of symptomatic influenza illnesses to be 4.4−34 million in 2011-2012 and 23−102 million in 2012-2013.ConclusionsWe illustrate that monitoring a representative group within a population may aid in effectively modelling the transmission of infectious diseases such as influenza. In particular, the utilization of RCTs in models may enhance the accuracy of epidemiological parameter estimation.

Quantifying How Different Clinical Presentations, Levels of Severity, and Healthcare Attendance Shape the Burden of Influenza-associated Illness: A Modeling Study From South Africa.

Burden estimates of medically and nonmedically attended influenza-associated illness across syndromes and levels of severity are lacking. We estimated the national burden of medically and nonmedically attended influenza-associated illness among individuals with different clinical presentations (all-respiratory, all-circulatory, and nonrespiratory/noncirculatory) and levels of severity (mild, fatal, and severe, nonfatal) using a combination of case-based (from laboratory-confirmed influenza surveillance) and ecological studies, as well as data from healthcare utilization surveys in South Africa during 2013-2015. In addition, we compared estimates of medically attended influenza-associated respiratory illness, obtained from case-based and ecological studies. Rates were reported per 100 000 individuals in the population. The estimated mean annual number of influenza-associated illness episodes was 10 737 847 (19.8% of 54 096 705 inhabitants). Of these episodes, 10 598 138 (98.7%) were mild, 128 173 (1.2%) were severe, nonfatal, and 11 536 (0.1%) were fatal. There were 2 718 140 (25.6%) mild, 56 226 (43.9%) severe, nonfatal, and 4945 (42.8%) medically attended should be after fatal episodes. Influenza-associated respiratory illness accounted for 99.2% (10 576 146) of any mild, 65.5% (83 941) of any severe, nonfatal, and 33.7% (3893) of any fatal illnesses. Ecological and case-based estimates of medically attended, influenza-associated, respiratory mild (rates: ecological, 1778.8, vs case-based, 1703.3; difference, 4.4%), severe, nonfatal (rates: ecological, 88.6, vs case-based, 75.3; difference, 15.0%), and fatal (rates: ecological, 3.8, vs case-based, 3.5; difference, 8.4%) illnesses were similar. There was a substantial burden of influenza-associated symptomatic illness, including severe, nonfatal and fatal illnesses, and a large proportion was nonmedically attended. Estimates, including only influenza-associated respiratory illness, substantially underestimated influenza-associated, severe, nonfatal and fatal illnesses. Ecological and case-based estimates were found to be similar for the compared categories.

A severe 2017 influenza season dominated by influenza A(H3N2), Victoria, Australia.

Surveillance for influenza-like illness (ILI) and laboratory-confirmed influenza in Victoria, Australia is undertaken jointly by the Victorian Infectious Diseases Reference Laboratory and the Victorian Government Department of Health and Human Services from May to October each year. Surveillance data comprise notifiable laboratory-confirmed influenza and ILI reporting from from two sources – a general practice sentinel surveillance programme and a locum service.The magnitude of the 2017 influenza season was high in Victoria with widespread circulation of influenza type A(H3N2), which peaked in September. A record number of laboratory-confirmed influenza cases were notified, and the proportion of ILI cases to total consultations from both the general practice and locum service were higher than previous years. Notified cases of influenza A were older than influenza B cases with 25% compared to 17% aged more than 65 years, respectively. The proportion of swabs that were positive for influenza peaked at 58%. Antigenic characterization suggested a good match between the circulating and vaccine strains of influenza A(H3N2).Most of the increases observed in notified cases of laboratory-confirmed influenza in recent years in Victoria have been attributed to increases in testing. However, that cases of ILI also increased in Victoria in 2017 is suggestive that 2017 was a relatively severe season. The dominance of influenza type A(H3N2), the extended duration of elevated activity, and a potential phylogenetic mismatch of vaccine to circulating strains are likely to have contributed to the relative severity of the 2017 season.Victoria is Australia’s second most populous state and is the mainland’s southernmost state. It has a temperate climate with an influenza season usually occurring in the cooler months between May and October. The Victorian Infectious Diseases Reference Laboratory (VIDRL), in partnership with the Victorian Government Department of Health and Human Services (DHHS), coordinates influenza-like illness (ILI) and laboratory-confirmed influenza surveillance in Victoria. There are three data sources included in the influenza surveillance system.

2496. A Comparative Evaluation of the Burden of Disease Caused by Influenza A and Influenza B During the 2011–2012, 2012–2013, and 2013–2014 Influenza Seasons in Canada

BackgroundWhen assessing burden of influenza disease, influenza B has typically been associated with infection in children and young adults, and is considered less prevalent and/or severe in older adults. We sought to assess the burden of influenza type A disease compared with influenza type B disease in Canadian adults admitted to hospital with laboratory-confirmed influenza.MethodsThe Serious Outcomes Surveillance (SOS) Network of the Canadian Immunization Research Network (CIRN) conducted active surveillance for laboratory-confirmed influenza in adults (≥16 years) hospitalized across Canada during the 2011–2014 influenza seasons. Eligible patients who were admitted to hospital with any acute respiratory illness or symptom had a nasopharyngeal swab collected and tested for influenza virus using reverse transcriptase polymerase chain reaction (PCR). Demographic/clinical information, as well as in-hospital outcomes were collected. Frailty Index scores were also recorded at baseline and 30-days after discharge, when possible, in patients ≥65 years. Patients with influenza A and B were compared using descriptive statistics; discrete outcomes were compared using Chi-squared (χ2) tests; continuous outcomes were compared using student’s t-tests.ResultsOverall, there were 3484 influenza A cases and 1375 influenza B cases enrolled in the SOS Network from 2011 to 2014. Mean age was significantly different between influenza A and influenza B cases (mean age of influenza A: 65.8, mean age of influenza B: 71.2, P < 0.01). A significantly larger proportion of influenza B patients were admitted from long-term care (A: 5.5%, B: 12.1%, P < 0.01). There was no significant difference with respect to length of hospitalization (influenza A: 11.1 days, influenza B: 10.27 days, P = 0.07) or mortality (A: 9.01%, B: 9.45%, P = 0.63) between influenza A and B. Patients with influenza B were significantly more frail prior to the onset of illness (A: 0.21, B: 0.22, P < 0.01).ConclusionCurrent attitudes consider influenza A to be the more significant virus in terms of morbidity and mortality in adults. However, influenza B is responsible for similar duration of hospitalization and similar mortality rates. In addition, influenza B predominantly affected the frail elderly and thus optimizing influenza B protection is important in this population.Disclosures M. K. Andrew, GSK: Grant Investigator, Research grant. Pfizer: Grant Investigator, Research grant. Sanofi Pasteur: Grant Investigator, Research grant. T. F. Hatchette, GSK: Grant Investigator, Research grant. Pfizer: Grant Investigator, Research grant. Abbvie: Consultant, Speaker honorarium. S. A. McNeil, GSK: Grant Investigator, Research grant. Pfizer: Grant Investigator, Research grant. Merck: Collaborator and Consultant, Contract clinical trials and Speaker honorarium. Novartis: Collaborator, Contract clinical trials. Sanofi Pasteur: Collaborator, Contract clinical trials.

Quantifying How Different Clinical Presentations, Levels of Severity and Healthcare Attendance Shape the Burden of Influenza-Associated Illness: A Modeling Study from South Africa

Background Burden estimates of medically and nonmedically attended influenza-associated illness across syndromes and levels of severity are lacking. Methods We estimated the national burden of medically and nonmedically attended influenza-associated illness among individuals with different clinical presentations (all-respiratory, all-circulatory, and nonrespiratory/noncirculatory) and levels of severity (mild, fatal, and severe, nonfatal) using a combination of case-based (from laboratory-confirmed influenza surveillance) and ecological studies, as well as data from healthcare utilization surveys in South Africa during 2013-2015. In addition, we compared estimates of medically attended influenza-associated respiratory illness, obtained from case-based and ecological studies. Rates were reported per 100 000 individuals in the population. Results The estimated mean annual number of influenza-associated illness episodes was 10 737 847 (19.8% of 54 096 705 inhabitants). Of these episodes, 10 598 138 (98.7%) were mild, 128 173 (1.2%) were severe, nonfatal, and 11 536 (0.1%) were fatal. There were 2 718 140 (25.6%) mild, 56 226 (43.9%) severe, nonfatal, and 4945 (42.8%) medically attended should be after fatal episodes. Influenza-associated respiratory illness accounted for 99.2% (10 576 146) of any mild, 65.5% (83 941) of any severe, nonfatal, and 33.7% (3893) of any fatal illnesses. Ecological and case-based estimates of medically attended, influenza-associated, respiratory mild (rates: ecological, 1778.8, vs case-based, 1703.3; difference, 4.4%), severe, nonfatal (rates: ecological, 88.6, vs case-based, 75.3; difference, 15.0%), and fatal (rates: ecological, 3.8, vs case-based, 3.5; difference, 8.4%) illnesses were similar. Conclusions There was a substantial burden of influenza-associated symptomatic illness, including severe, nonfatal and fatal illnesses, and a large proportion was nonmedically attended. Estimates, including only influenza-associated respiratory illness, substantially underestimated influenza-associated, severe, nonfatal and fatal illnesses. Ecological and case-based estimates were found to be similar for the compared categories.

Establishing seasonal and alert influenza thresholds in Cambodia using the WHO method: implications for effective utilization of influenza surveillance in the tropics and subtropics.

ObjectiveTo establish seasonal and alert thresholds and transmission intensity categories for influenza to provide timely triggers for preventive measures or upscaling control measures in Cambodia.MethodsUsing Cambodia’s influenza-like illness (ILI) and laboratory-confirmed influenza surveillance data from 2009 to 2015, three parameters were assessed to monitor influenza activity: the proportion of ILI patients among all outpatients, proportion of ILI samples positive for influenza and the product of the two. With these parameters, four threshold levels (seasonal, moderate, high and alert) were established and transmission intensity was categorized based on a World Health Organization alignment method. Parameters were compared against their respective thresholds.ResultsDistinct seasonality was observed using the two parameters that incorporated laboratory data. Thresholds established using the composite parameter, combining syndromic and laboratory data, had the least number of false alarms in declaring season onset and were most useful in monitoring intensity. Unlike in temperate regions, the syndromic parameter was less useful in monitoring influenza activity or for setting thresholds.ConclusionInfluenza thresholds based on appropriate parameters have the potential to provide timely triggers for public health measures in a tropical country where monitoring and assessing influenza activity has been challenging. Based on these findings, the Ministry of Health plans to raise general awareness regarding influenza among the medical community and the general public. Our findings have important implications for countries in the tropics/subtropics and in resource-limited settings, and categorized transmission intensity can be used to assess severity of potential pandemic influenza as well as seasonal influenza.

Effectiveness of seasonal influenza vaccine in Australia, 2015: An epidemiological, antigenic and phylogenetic assessment

BackgroundA record number of laboratory-confirmed influenza cases were notified in Australia in 2015, during which type A(H3) and type B Victoria and Yamagata lineages co-circulated. We estimated effectiveness of the 2015 inactivated seasonal influenza vaccine against specific virus lineages and clades. MethodsThree sentinel general practitioner networks conduct surveillance for laboratory-confirmed influenza amongst patients presenting with influenza-like illness in Australia. Data from the networks were pooled to estimate vaccine effectiveness (VE) for seasonal trivalent influenza vaccine in Australia in 2015 using the case test-negative study design. ResultsThere were 2443 eligible patients included in the study, of which 857 (35%) were influenza-positive. Thirty-three and 19% of controls and cases respectively were reported as vaccinated. Adjusted VE against all influenza was 54% (95% CI: 42, 63). Antigenic characterisation data suggested good match between vaccine and circulating strains of A(H3); however VE for A(H3) was low at 44% (95% CI: 21, 60). Phylogenetic analysis indicated most circulating viruses were from clade 3C.2a, rather than the clade included in the vaccine (3C.3a). VE point estimates were higher against B/Yamagata lineage influenza (71%; 95% CI: 57, 80) than B/Victoria (42%, 95% CI: 13, 61), and in younger people. ConclusionsOverall seasonal vaccine was protective against influenza infection in Australia in 2015. Higher VE against the B/Yamagata lineage included in the trivalent vaccine suggests that more widespread use of quadrivalent vaccine could have improved overall effectiveness of influenza vaccine. Genetic characterisation suggested lower VE against A(H3) influenza was due to clade mismatch of vaccine and circulating viruses.

Using Laboratory Data to Aid Early Warning in Prospective Influenza Mortality Surveillance

Many countries prospectively monitor influenza-attributable mortality using a variation of the Serfling seasonal time series model. Our aim is to demonstrate use of routine laboratory-confirmed influenza surveillance data to forecast predicted influenza-attributable deaths during the current influenza season. The two models provided a reasonable forecast for 2012. The model forecasts of weekly deaths during 2012 were compared against observed deaths using root mean squared error (RMSE). The results shown that the model including influenza type A and B provided a better fit. Here, we demonstrated a time series model for influenza-attributable mortality surveillance based on laboratory surveillance information.

Understanding the burden of influenza infection among adults in Canadian hospitals: A comparison of the 2009-2010 pandemic season with the prepandemic and postpandemic seasons

The degree to which the 2009-2010 influenza pandemic season differed from previous and subsequent influenza seasons in Canadian hospitals has not yet been assessed. Surveillance for laboratory-confirmed influenza among adults in 51 Canadian Nosocomial Infection Surveillance Program hospitals was conducted between November 1, 2006, and May 31, 2011. Inpatient characteristics, treatment, and outcomes of influenza cases in the pandemic season (2009-2010) were compared with those in the prepandemic (2006-2007 to 2008-2009) and postpandemic (2010-2011) seasons. The incidence of influenza infection was lower in the postpandemic season (1.59/1,000 admissions) compared with the prepandemic seasons (2.00/1,000 admissions; P < .001) and the pandemic season (1.80/1,000 admissions; P < .001). The proportion of cases classified as health care-associated was much smaller during the pandemic season (6.6%) than in either the prepandemic season (23.2%; P < .001) or the postpandemic season (23.6%; P < .001). Inpatients in the pandemic season were significantly younger compared with those in the prepandemic and postpandemic seasons (P < .001). Inpatients in the pandemic season were less likely to have been vaccinated (P < .001), but more likely to be treated with antiviral agents (P < .001), than inpatients in both the prepandemic and postpandemic seasons. Intensive care unit admission was greater during the pandemic season, but there were no significant differences in 30-day mortality among the seasons. Among adult inpatients, the pH1N1 pandemic season differed from seasonal influenza in terms of age, vaccination status, antiviral use, and intensive care unit admission, but not in terms of 30-day mortality.

The Burden of Influenza in Young Children, 2004–2009

To characterize the health care burden of influenza from 2004 through 2009, years when influenza vaccine recommendations were expanded to all children aged ≥6 months. Population-based surveillance for laboratory-confirmed influenza was performed among children aged <5 years presenting with fever and/or acute respiratory illness to inpatient and outpatient settings during 5 influenza seasons in 3 US counties. Enrolled children had nasal/throat swabs tested for influenza by reverse transcriptase-polymerase chain reaction and their medical records reviewed. Rates of influenza hospitalizations per 1000 population and proportions of outpatients (emergency department and clinic) with influenza were computed. The study population comprised 2970, 2698, and 2920 children from inpatient, emergency department, and clinic settings, respectively. The single-season influenza hospitalization rates were 0.4 to 1.0 per 1000 children aged <5 years and highest for infants <6 months. The proportion of outpatient children with influenza ranged from 10% to 25% annually. Among children hospitalized with influenza, 58% had physician-ordered influenza testing, 35% had discharge diagnoses of influenza, and 2% received antiviral medication. Among outpatients with influenza, 7% were tested for influenza, 7% were diagnosed with influenza, and <1% had antiviral treatment. Throughout the 5 study seasons, <45% of influenza-negative children ≥6 months were fully vaccinated against influenza. Despite expanded vaccination recommendations, many children are insufficiently vaccinated, and substantial influenza burden remains. Antiviral use was low. Future studies need to evaluate trends in use of vaccine and antiviral agents and their impact on disease burden and identify strategies to prevent influenza in young infants.

Seasonality, Timing, and Climate Drivers of Influenza Activity Worldwide

Although influenza is a vaccine-preventable disease that annually causes substantial disease burden, data on virus activity in tropical countries are limited. We analyzed publicly available influenza data to better understand the global circulation of influenza viruses. We reviewed open-source, laboratory-confirmed influenza surveillance data. For each country, we abstracted data on the percentage of samples testing positive for influenza each epidemiologic week from the annual number of samples testing positive for influenza. The start of influenza season was defined as the first week when the proportion of samples that tested positive remained above the annual mean. We assessed the relationship between percentage of samples testing positive and mean monthly temperature with use of regression models. We identified data on laboratory-confirmed influenza virus infection from 85 countries. More than one influenza epidemic period per year was more common in tropical countries (41%) than in temperate countries (15%). Year-round activity (ie, influenza virus identified each week having ≥ 10 specimens submitted) occurred in 3 (7%) of 43 temperate, 1 (17%) of 6 subtropical, and 11 (37%) of 30 tropical countries with available data (P = .006). Percentage positivity was associated with low temperature (P = .001). Annual influenza epidemics occur in consistent temporal patterns depending on climate.

Moderate influenza vaccine effectiveness in Victoria, Australia, 2011

We used a sentinel general practitioner (GP) network to conduct surveillance for laboratory-confirmed influenza amongst patients presenting with influenza-like illness (ILI) in Victoria, Australia in 2011. The test negative variation of the case control study design was used to estimate effectiveness for seasonal trivalent influenza vaccine. Cases and controls were ILI patients that tested positive and negative for influenza, respectively. Vaccination status was recorded by GPs and vaccine effectiveness (VE) was calculated as (1-adjusted odds ratio)x100%. There were 529 patients included in the study, of which 29% were influenza positive. Twelve percent of study participants were reported as vaccinated, 6% of cases and 15% of controls. Adjusted VE against all influenza was 56%, but not statistically significant. There was generally little variation in VE estimates when stratified by virus type and subtype, which is consistent with good matches between circulating strains and the vaccine strains. The VE was higher among adults of working age than among children.

Monitoring Influenza Activity in the United States: A Comparison of Traditional Surveillance Systems with Google Flu Trends

BackgroundGoogle Flu Trends was developed to estimate US influenza-like illness (ILI) rates from internet searches; however ILI does not necessarily correlate with actual influenza virus infections.Methods and FindingsInfluenza activity data from 2003–04 through 2007–08 were obtained from three US surveillance systems: Google Flu Trends, CDC Outpatient ILI Surveillance Network (CDC ILI Surveillance), and US Influenza Virologic Surveillance System (CDC Virus Surveillance). Pearson's correlation coefficients with 95% confidence intervals (95% CI) were calculated to compare surveillance data. An analysis was performed to investigate outlier observations and determine the extent to which they affected the correlations between surveillance data. Pearson's correlation coefficient describing Google Flu Trends and CDC Virus Surveillance over the study period was 0.72 (95% CI: 0.64, 0.79). The correlation between CDC ILI Surveillance and CDC Virus Surveillance over the same period was 0.85 (95% CI: 0.81, 0.89). Most of the outlier observations in both comparisons were from the 2003–04 influenza season. Exclusion of the outlier observations did not substantially improve the correlation between Google Flu Trends and CDC Virus Surveillance (0.82; 95% CI: 0.76, 0.87) or CDC ILI Surveillance and CDC Virus Surveillance (0.86; 95%CI: 0.82, 0.90).ConclusionsThis analysis demonstrates that while Google Flu Trends is highly correlated with rates of ILI, it has a lower correlation with surveillance for laboratory-confirmed influenza. Most of the outlier observations occurred during the 2003–04 influenza season that was characterized by early and intense influenza activity, which potentially altered health care seeking behavior, physician testing practices, and internet search behavior.

When should a diagnosis of influenza be considered in adults requiring intensive care unit admission? Results of population-based active surveillance in Toronto

IntroductionThere is a paucity of data about the clinical characteristics that help identify patients at high risk of influenza infection upon ICU admission. We aimed to identify predictors of influenza infection in patients admitted to ICUs during the 2007/2008 and 2008/2009 influenza seasons and the second wave of the 2009 H1N1 influenza pandemic as well as to identify populations with increased likelihood of seasonal and pandemic 2009 influenza (pH1N1) infection.MethodsSix Toronto acute care hospitals participated in active surveillance for laboratory-confirmed influenza requiring ICU admission during periods of influenza activity from 2007 to 2009. Nasopharyngeal swabs were obtained from patients who presented to our hospitals with acute respiratory or cardiac illness or febrile illness without a clear nonrespiratory aetiology. Predictors of influenza were assessed by multivariable logistic regression analysis and the likelihood of influenza in different populations was calculated.ResultsIn 5,482 patients, 126 (2.3%) were found to have influenza. Admission temperature ≥38°C (odds ratio (OR) 4.7 for pH1N1, 2.3 for seasonal influenza) and admission diagnosis of pneumonia or respiratory infection (OR 7.3 for pH1N1, 4.2 for seasonal influenza) were independent predictors for influenza. During the peak weeks of influenza seasons, 17% of afebrile patients and 27% of febrile patients with pneumonia or respiratory infection had influenza. During the second wave of the 2009 pandemic, 26% of afebrile patients and 70% of febrile patients with pneumonia or respiratory infection had influenza.ConclusionsThe findings of our study may assist clinicians in decision making regarding optimal management of adult patients admitted to ICUs during future influenza seasons. Influenza testing, empiric antiviral therapy and empiric infection control precautions should be considered in those patients who are admitted during influenza season with a diagnosis of pneumonia or respiratory infection and are either febrile or admitted during weeks of peak influenza activity.

Burden of Seasonal Influenza Hospitalization in Children, United States, 2003 to 2008

To estimate the rates of hospitalization with seasonal influenza in children aged <18 years from a large, diverse surveillance area during 2003 to 2008. Through the Emerging Infections Program Network, population-based surveillance for laboratory-confirmed influenza was conducted in 10 states, including 5.3 million children. Hospitalized children were identified retrospectively; clinicians made influenza testing decisions. Data collected from the hospital record included demographics, medical history, and clinical course. Incidence rates were calculated with census data. The highest hospitalization rates occurred in children aged <6 months (seasonal range, 9-30/10 000 children), and the lowest rates occurred in children aged 5 to 17 years (0.3-0.8/10 000). Overall, 4015 children were hospitalized, 58% of whom were identified with rapid diagnostic tests alone. Forty percent of the children who were hospitalized had underlying medical conditions; asthma (18%), prematurity (15% of children aged <2 years), and developmental delay (7%) were the most common. Severe outcomes included intensive care unit admission (12%), respiratory failure (5%), bacterial coinfection (2%), and death (0.5%). Influenza-associated hospitalization rates varied by season and age and likely underestimate true rates because many hospitalized children are not tested for influenza. The proportion of children with severe outcomes was substantial across seasons. Quantifying incidence of influenza hospitalization and severe outcomes is critical to defining disease burden.

Epidemiology of influenza-associated hospitalization in adults, Toronto, 2007/8.

The purpose of this investigation was to identify when diagnostic testing and empirical antiviral therapy should be considered for adult patients requiring hospitalization during influenza seasons. During the 2007/8 influenza season, six acute care hospitals in the Greater Toronto Area participated in active surveillance for laboratory-confirmed influenza requiring hospitalization. Nasopharyngeal (NP) swabs were obtained from patients presenting with acute respiratory or cardiac illness, or with febrile illness without clear non-respiratory etiology. Predictors of influenza were analyzed by multivariable logistic regression analysis and likelihoods of influenza infection in various patient groups were calculated. Two hundred and eighty of 3,917 patients were found to have influenza. Thirty-five percent of patients with influenza presented with a triage temperature ≥38.0°C, 80% had respiratory symptoms in the emergency department, and 76% were ≥65 years old. Multivariable analysis revealed a triage temperature ≥38.0°C (odds ratio [OR] 3.1; 95% confidence interval [CI] 2.3–4.1), the presence of respiratory symptoms (OR 1.7; 95% CI 1.2–2.4), admission diagnosis of respiratory infection (OR 1.8; 95% CI 1.3–2.4), admission diagnosis of exacerbation of chronic obstructive pulmonary disease (COPD)/asthma or respiratory failure (OR 2.3; 95% CI 1.6–3.4), and admission in peak influenza weeks (OR 4.2; 95% CI 3.1–5.7) as independent predictors of influenza. The likelihood of influenza exceeded 15% in patients with respiratory infection or exacerbation of COPD/asthma if the triage temperature was ≥38.0°C or if they were admitted in the peak weeks during the influenza season. During influenza season, diagnostic testing and empiric antiviral therapy should be considered in patients requiring hospitalization if respiratory infection or exacerbation of COPD/asthma are suspected and if either the triage temperature is ≥38.0°C or admission is during the weeks of peak influenza activity.

Global Patterns in Seasonal Activity of Influenza A/H3N2, A/H1N1, and B from 1997 to 2005: Viral Coexistence and Latitudinal Gradients

Despite a mass of research on the epidemiology of seasonal influenza, overall patterns of infection have not been fully described on broad geographic scales and for specific types and subtypes of the influenza virus. Here we provide a descriptive analysis of laboratory-confirmed influenza surveillance data by type and subtype (A/H3N2, A/H1N1, and B) for 19 temperate countries in the Northern and Southern hemispheres from 1997 to 2005, compiled from a public database maintained by WHO (FluNet). Key findings include patterns of large scale co-occurrence of influenza type A and B, interhemispheric synchrony for subtype A/H3N2, and latitudinal gradients in epidemic timing for type A. These findings highlight the need for more countries to conduct year-round viral surveillance and report reliable incidence data at the type and subtype level, especially in the Tropics.

Multistate Surveillance for Laboratory-Confirmed, Influenza-Associated Hospitalizations in Children

Increasing use of rapid influenza diagnostics facilitates laboratory confirmation of influenza infections. We describe laboratory-confirmed, influenza-associated hospitalizations in a population representing almost 6% of children in the United States. We conducted population-based surveillance for influenza-associated hospitalizations between October 1, 2003, and March 31, 2004, in 54 counties in 9 states (4.2 million children) participating in the Emerging Infections Program Network. Clinical characteristics, predictors of intensive care unit admission and geographic and age-specific incidence were evaluated. Surveillance identified 1,308 case-patients; 80% were <5 years and 27% were <6 months of age. Half of the patients and 4 of 5 pediatric deaths did not have a medical indication for influenza vaccination and were outside the 6- to 23-month age group. Twenty-eight percent of case-patients had radiographic evidence of a pulmonary infiltrate, 11% were admitted to intensive care and 3% received mechanical ventilation. The median length of hospital stay was 2 days. Community-acquired invasive bacterial coinfections (1% of patients) were associated with intensive care admission (adjusted odds ratio, 16.9; 95% confidence interval, 5.0-56.8). Thirty-five percent of patients >or=6 months old had received at least one influenza vaccine dose that season. The overall incidence of influenza-associated hospitalizations was 36 per 100,000 children (range per state, 10 per 100,000 to 86 per 100,000). Influenza was an important cause of hospitalizations in children during 2003-2004. Hospitalizations were particularly common among children <6 months of age, a group for whom influenza vaccine is not licensed. Continued surveillance for laboratory-confirmed influenza could inform prevention strategies.