Age- and influenza activity-stratified case definitions of influenza-like illness: experience from hospital-based influenza surveillance in South Korea

SARS-CoV-2, influenza A/B and respiratory syncytial virus positivity and association with influenza-like illness and self-reported symptoms, over the 2022/23 winter season in the UK: a longitudinal surveillance cohort

BACKGROUND

Syndromic surveillance often relies on patients presenting to healthcare. Community cohorts, although more challenging to recruit, could provide additional population-wide insights, particularly with SARS-CoV-2 co-circulating with other respiratory viruses.

METHODS

We estimated the positivity and incidence of SARS-CoV-2, influenza A/B, and RSV, and trends in self-reported symptoms including influenza-like illness (ILI), over the 2022/23 winter season in a broadly representative UK community cohort (COVID-19 Infection Survey), using negative-binomial generalised additive models. We estimated associations between test positivity and each of the symptoms and influenza vaccination, using adjusted logistic and multinomial models.

RESULTS

Swabs taken at 32,937/1,352,979 (2.4%) assessments tested positive for SARS-CoV-2, 181/14,939 (1.2%) for RSV and 130/14,939 (0.9%) for influenza A/B, varying by age over time. Positivity and incidence peaks were earliest for RSV, then influenza A/B, then SARS-CoV-2, and were highest for RSV in the youngest and for SARS-CoV-2 in the oldest age groups. Many test positives did not report key symptoms: middle-aged participants were generally more symptomatic than older or younger participants, but still, only ~ 25% reported ILI-WHO and ~ 60% ILI-ECDC. Most symptomatic participants did not test positive for any of the three viruses. Influenza A/B-positivity was lower in participants reporting influenza vaccination in the current and previous seasons (odds ratio = 0.55 (95% CI 0.32, 0.95)) versus neither season.

CONCLUSIONS

Symptom profiles varied little by aetiology, making distinguishing SARS-CoV-2, influenza and RSV using symptoms challenging. Most symptoms were not explained by these viruses, indicating the importance of other pathogens in syndromic surveillance. Influenza vaccination was associated with lower rates of community influenza test positivity.

Applying symptom dynamics to accurately predict influenza virus infection: An international multicenter influenza-like illness surveillance study

BACKGROUND

Public health organizations have recommended various definitions of influenza-like illnesses under the assumption that the symptoms do not change during influenza virus infection. To explore the relationship between symptoms and influenza over time, we analyzed a dataset from an international multicenter prospective emergency department (ED)-based influenza-like illness cohort study.

METHODS

We recruited patients in the US and Taiwan between 2015 and 2020 with: (1) flu-like symptoms (fever and cough, headache, or sore throat), (2) absence of any of the respiratory infection symptoms, or (3) positive laboratory test results for influenza from the current ED visit. We evaluated the association between the symptoms and influenza virus infection on different days of illness. The association was evaluated among different subgroups, including different study countries, influenza subtypes, and only patients with influenza.

RESULTS

Among the 2471 recruited patients, 45.7% tested positive for influenza virus. Cough was the most predictive symptom throughout the week (odds ratios [OR]: 7.08-11.15). In general, all symptoms were more predictive during the first 2 days (OR: 1.55-10.28). Upper respiratory symptoms, such as sore throat and productive cough, and general symptoms, such as body ache and fatigue, were more predictive in the first half of the week (OR: 1.51-3.25). Lower respiratory symptoms, such as shortness of breath and wheezing, were more predictive in the second half of the week (OR: 1.52-2.52). Similar trends were observed for most symptoms in the different subgroups.

CONCLUSIONS

The time course is an important factor to be considered when evaluating the symptoms of influenza virus infection.

Evaluation of influenza case definitions for use in real-world evidence research

Background

Laboratory confirmation of influenza is not routinely done in practice. With the advent of big data, it is tempting to use healthcare administrative databases for influenza vaccine effectiveness studies, which often rely on clinical diagnosis codes. The objective of this article is to compare influenza incidence curves using international case definitions derived from clinical diagnostic codes with influenza surveillance data from the United States (US) Centers for Disease Control and Prevention (CDC).

Methods

This case series describes influenza incidence by CDC week, defined using International Classification of Disease diagnostic codes over four influenza seasons (2015-2016 to 2018-2019) in a cohort of US individuals three years of age and older who consulted at least once per year between 2015 and 2019. Results were compared to the number of influenza-positive specimens or outpatient visits for influenza-like illness obtained from the CDC flu surveillance data.

Results

The incidence curves of influenza-related medical encounters were very similar to the CDC's surveillance data for laboratory-confirmed influenza. Conversely, the number of influenza-like illness encounters was high when influenza viruses started to circulate, leading to a discrepancy with CDC-reported data.

Conclusion

A specific case definition should be prioritized when data for laboratory-confirmed influenza are not available, as a broader case definition would conservatively bias influenza vaccine effectiveness toward the null.

Does knowing the influenza epidemic threshold has been reached influence the performance of influenza case definitions?

Background

Disease surveillance using adequate case definitions is very important. The objective of the study was to compare the performance of influenza case definitions and influenza symptoms in the first two epidemic weeks with respect to other epidemic weeks.

Methods

We analysed cases of acute respiratory infection detected by the network of sentinel primary care physicians of Catalonia for 10 seasons. We calculated the diagnostic odds ratio (DOR) and 95% confidence intervals (CI) for the first two epidemic weeks and for other epidemic weeks.

Results

A total of 4,338 samples were collected in the epidemic weeks, of which 2,446 (56.4%) were positive for influenza. The most predictive case definition for laboratory-confirmed influenza was the WHO case definition for influenza-like illness (ILI) in the first two epidemic weeks (DOR 2.10; 95% CI 1.57–2.81) and in other epidemic weeks (DOR 2.31; 95% CI 1.96–2.72). The most predictive symptom was fever. After knowing that epidemic threshold had been reached, the DOR of the ILI WHO case definition in children aged <5 years and cough and fever in this group increased (190%, 170% and 213%, respectively).

Conclusions

During influenza epidemics, differences in the performance of the case definition and the discriminative ability of symptoms were found according to whether it was known that the epidemic threshold had been reached or not. This suggests that sentinel physicians are stricter in selecting samples to send to the laboratory from patients who present symptoms more specific to influenza after rather than before an influenza epidemic has been declared.

Performance of Symptom-Based Case Definitions to Identify Influenza Virus Infection Among Pregnant Women in Middle-Income Countries: Findings From the Pregnancy and Influenza Multinational Epidemiologic (PRIME) Study

BACKGROUND

The World Health Organization (WHO) recommends case definitions for influenza surveillance that are also used in public health research, although their performance has not been assessed in many risk groups, including pregnant women in whom influenza may manifest differently. We evaluated the performance of symptom-based definitions to detect influenza in a cohort of pregnant women in India, Peru, and Thailand.

METHODS

In 2017 and 2018, we contacted 11 277 pregnant women twice weekly during the influenza season to identify illnesses with new or worsened cough, runny nose, sore throat, difficulty breathing, or myalgia and collected data on other symptoms and nasal swabs for influenza real-time reverse transcription-polymerase chain reaction (rRT-PCR) testing. We calculated sensitivity, specificity, positive-predictive value, and negative-predictive value of each symptom predictor, WHO respiratory illness case definitions, and a de novo definition derived from results of multivariable modeling.

RESULTS

Of 5444 eligible illness episodes among 3965 participants, 310 (6%) were positive for influenza. In a multivariable model, measured fever ≥38°C (adjusted odds ratio [95% confidence interval], 4.6 [3.1-6.8]), myalgia (3.0 [2.2-4.0]), cough (2.7 [1.9-3.9]), and chills (1.6 [1.1-2.4]) were independently associated with influenza illness. A definition based on these 4 (measured fever, cough, chills, or myalgia) was 95% sensitive and 27% specific. The WHO influenza-like illness (ILI) definition was 16% sensitive and 98% specific.

CONCLUSIONS

The current WHO ILI case definition was highly specific but had low sensitivity. The intended use of case definitions should be considered when evaluating the tradeoff between sensitivity and specificity.

Influenza surveillance case definitions miss a substantial proportion of older adults hospitalized with laboratory-confirmed influenza: A report from the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) Network

OBJECTIVE

Older adults often have atypical presentation of illness and are particularly vulnerable to influenza and its sequelae, making the validity of influenza case definitions particularly relevant. We sought to assess the performance of influenza-like illness (ILI) and severe acute respiratory illness (SARI) criteria in hospitalized older adults.

DESIGN

Prospective cohort study.

SETTING

The Serious Outcomes Surveillance Network of the Canadian Immunization Research Network undertakes active surveillance for influenza among hospitalized adults.

METHODS

Data were pooled from 3 influenza seasons: 2011/12, 2012/13, and 2013/14. The ILI and SARI criteria were defined clinically, and influenza was laboratory confirmed. Frailty was measured using a validated frailty index.

RESULTS

Of 11,379 adult inpatients (7,254 aged ≥65 years), 4,942 (2,948 aged ≥65 years) had laboratory-confirmed influenza. Their median age was 72 years (interquartile range [IQR], 58-82) and 52.6% were women. The sensitivity of ILI criteria was 51.1% (95% confidence interval [CI], 49.6-52.6) for younger adults versus 44.6% (95% CI, 43.6-45.8) for older adults. SARI criteria were met by 64.1% (95% CI, 62.7-65.6) of younger adults versus 57.1% (95% CI, 55.9-58.2) of older adults with laboratory-confirmed influenza. Patients with influenza who were prefrail or frail were less likely to meet ILI and SARI case definitions.

CONCLUSIONS

A substantial proportion of older adults, particularly those who are frail, are missed by standard ILI and SARI case definitions. Surveillance using these case definitions is biased toward identifying younger cases, and does not capture the true burden of influenza. Because of the substantial fraction of cases missed, surveillance definitions should not be used to guide diagnosis and clinical management of influenza.

Short-term effects of multiple outdoor environmental factors on risk of asthma exacerbations: Age-stratified time-series analysis

BACKGROUND

Although the different age groups had differences in sensitivity of asthma exacerbations (AEs) to environmental factors, no comprehensive study has examined the age-stratified effects of environmental factors on AEs.

OBJECTIVE

We sought to examine the short-term effects in age-stratified groups (infants, preschool children, school-aged children, adults, and the elderly) of outdoor environmental factors (air pollutants, weather conditions, aeroallergens, and respiratory viral epidemics) on AEs.

METHODS

We performed an age-stratified analysis of the short-term effects of 4 groups of outdoor environmental factors on AEs in Seoul Metropolitan City (Korea) from 2008 and 2012. The statistical analysis used a Poisson generalized linear regression model, with a distributed lag nonlinear model for identification of lagged and nonlinear effects and convergent cross-mapping for identification of causal associations.

RESULTS

Analysis of the total population (n = 10,233,519) indicated there were 28,824 AE events requiring admission to an emergency department during the study period. Diurnal temperature range had significant effects in pediatric (infants, preschool children, and school-aged children) and elderly (relative risk [RR], 1.056-1.078 and 1.016, respectively) subjects. Tree and weed pollen, human rhinovirus, and influenza virus had significant effects in school-aged children (RR, 1.014, 1.040, 1.042, and 1.038, respectively). Tree pollen and influenza virus had significant effects in adults (RR, 1.026 and 1.044, respectively). Outdoor air pollutants (particulate matter of ≤10 μm in diameter, nitrogen dioxide, ozone, carbon monoxide, and sulfur dioxide) had significant short-term effects in all age groups (except for carbon monoxide and sulfur dioxide in infants).

CONCLUSION

These findings provide a need for the development of tailored strategies to prevent AE events in different age groups.

Cost-Benefit Analysis of Real-Time Influenza Testing for Patients in German Emergency Rooms

Background: Seasonal influenza causes significant morbidity worldwide and has a substantial economic impact on the healthcare system. Objective: To assess the cost–benefit relation of implementing a real-time influenza test in emergency rooms (ER) of German hospitals. Methods: A deterministic decision-analytic model was developed simulating the incremental costs of using the Solana^® Influenza A+B test, compared to those of using conventional clinical judgement alone to confirm or exclude influenza in adult ILI (influenza-like illness) patients, in German ER, prior to hospitalization. Direct costs were evaluated from the hospital perspective, considering resource use directly related to influenza testing and treatment, as well as indirect costs incurred by nosocomial influenza transmission. Results: Through base-case analysis and assuming an influenza prevalence of 42.6%, real-time testing with Solana^® reduced average costs of hospitalized ILI patients by €132.61, per tested patient. Moreover, the Solana^® saved €6.9 per tested patient in favor of the hospital. In probabilistic sensitivity analysis, under all reasonable assumptions, implementing the Solana^® saved on average €144.13 as compared to applying the clinical-judgement-only strategy, thus, it was found to be constantly less expensive. Conclusions: Using highly sensitive and specific real-time influenza tests in ILI patients at German ER might significantly reduce hospital expenditures

Factors Associated With Influenza in an Emergency Department Setting

BACKGROUND

Emergency departments (EDs) become more overcrowded during peak respiratory virus season. Distinguishing influenza from other viruses is crucial to implement social distancing practices, early treatment, and prompt disposition.

OBJECTIVES

We sought to determine factors associated with influenza among a prospective cohort of consecutive ED patients with acute respiratory illness (ARI).

METHODS

Between December 2016 and March 2017, trained research assistants screened consecutive ED patients with ARI symptoms. ARI criteria included measured fever at home or in the ED >38°C and a cough, sore throat, or rhinorrhea with a duration of symptoms >12 hours and <1 week. After consent, research assistants collected demographics and clinical history using a standardized data form, and patients had a polymerase chain reaction-based assay that is nearly 100% sensitive for influenza. Univariate analysis was conducted on all predictor variables. Significant variables were entered into a multivariate logistic regression model to find factors that were independently associated with influenza.

RESULTS

One hundred nineteen patients consented to enrollment and 31% were found to be positive for influenza. Myalgia, the absence of gastrointestinal symptoms (no diarrhea or vomiting), sore throat, chills, headache, and oxygen saturation ≥97% were significant on univariate analysis and were entered into the multivariate model. Myalgia (adjusted odds ratio [AOR] 3.9), the absence of gastrointestinal symptoms (AOR 4.7), and oxygen saturation ≥97% (AOR 2.8) were significant independent factors of influenza.

CONCLUSION

The presence of myalgia, the absence of gastrointestinal symptoms, and oxygen saturation ≥97% are factors that can help distinguish influenza from other acute respiratory illnesses in the ambulatory ED population.

Rapid Point-of-Care Influenza Testing for Patients in German Emergency Rooms - A Cost-Benefit Analysis

BACKGROUND

Each year, influenza causes significant morbidity and death worldwide and produces significant economic losses at the expense of the healthcare system.

OBJECTIVE

To assess the cost-benefit relationship of implementing a rapid point-of-care (POC) influenza test in emergency rooms (ERs) of German hospitals.

METHODS

A deterministic decision-analytic model simulated the incremental costs of using the Sofia^® Influenza A+B test compared to those of using clinical judgement alone to confirm or exclude influenza in adult ILI (influenza-like illness) patients in German ERs prior to hospitalization. Direct costs, with and without subsequent oseltamivir treatment, were evaluated from the hospital perspective as well as indirect costs incurred by nosocomial influenza transmission to hospital employees.

RESULTS

In base-case analysis, taking the influenza prevalence of 25.9% in the season 2018/2019 and assuming a hospitalization rate among influenza suspects of 21.9%, rapid testing with the Sofia^® followed by administering oseltamivir to patients testing positive reduced average costs of hospitalized ILI patients by €52.16 per tested patient. If oseltamivir was not offered, testing with the Sofia^® reduced costs by €42.28 in favor of the hospital.In probabilistic sensitivity analysis, under all reasonable assumptions, implementing the Sofia^® saved on average €119.89 as compared to applying the clinical-judgement-only strategy. The major part of the cost savings, €113.17 or 94.4%, was due to the POC test's high specificity, which led to 91% reduction in needless bed-blocking on the first day of hospitalization. However, as the sensitivity of 75.3% was only slightly higher than that of conventional clinical judgement, improved classification of patients with true influenza and a correspondingly lower rate of illness in hospital employees could not be achieved.

CONCLUSIONS

Using highly specific rapid POC influenza tests in ILI patients at German ER, despite their sub-optimal sensitivity, may significantly reduce hospital expenditures.

Effectiveness of influenza and pneumococcal polysaccharide vaccines against influenza-related outcomes including pneumonia and acute exacerbation of cardiopulmonary diseases: Analysis by dominant viral subtype and vaccine matching

Background

Influenza and pneumonia are leading causes of morbidity and mortality among the elderly. Although vaccination is a main strategy to prevent these infectious diseases, concerns remain with respect to vaccine effectiveness.

Methods

During three influenza seasons (2014–2015, 2015–2016 and 2016–2017), we evaluated the effectiveness of the influenza and pneumococcal vaccines against pneumonia and acute exacerbation of cardiopulmonary diseases among the elderly aged ≥65 years with influenza-like illness (ILI). Demographic and clinical data were collected prospectively.

Results

Among 2,119 enrolled cases, 1,302 (61.4%) and 871 (41.1%) received the influenza vaccine and 23-valent pneumococcal polysaccharide vaccine (PPV23), respectively. During an A/H3N2-dominant season with poor influenza vaccine effectiveness (2014–2015 season), neither the influenza vaccine nor PPV23 showed significant effectiveness against pneumonia or acute exacerbation of cardiopulmonary diseases. During seasons with good influenza vaccine effectiveness (2015–2016 and 2016–2017 seasons), the influenza vaccine was effective in preventing pneumonia, but PPV23 was not. In particular, the influenza vaccine was effective in preventing acute exacerbation of heart diseases (75.0%) during the A/H1N1-dominant 2015–2016 season.

Conclusion

The influenza vaccine was effective in preventing pneumonia only during vaccine-matched seasons with good effectiveness against circulating influenza viruses. In addition, the influenza vaccine was cardio-protective during a vaccine-matched A/H1N1-dominant season.

Performance of influenza case definitions for influenza community surveillance: based on the French influenza surveillance network GROG, 2009-2014

International case definitions recommended by the Centers for Disease Control and Prevention (CDC), the European Centre for Disease Prevention and Control (ECDC), and the World Health Organization (WHO) are commonly used for influenza surveillance. We evaluated clinical factors associated with the laboratory-confirmed diagnosis of influenza and the performance of these influenza case definitions by using a complete dataset of 14,994 patients with acute respiratory infection (ARI) from whom a specimen was collected between August 2009 and April 2014 by the Groupes Régionaux d'Observation de la Grippe (GROG), a French national influenza surveillance network. Cough and fever ≥ 39 °C most accurately predicted an influenza infection in all age groups. Several other symptoms were associated with an increased risk of influenza (headache, weakness, myalgia, coryza) or decreased risk (adenopathy, pharyngitis, shortness of breath, otitis/otalgia, bronchitis/ bronchiolitis), but not throughout all age groups. The WHO case definition for influenza-like illness (ILI) had the highest specificity with 21.4%, while the ECDC ILI case definition had the highest sensitivity with 96.1%. The diagnosis among children younger than 5 years remains challenging. The study compared the performance of clinical influenza definitions based on outpatient surveillance and will contribute to improving the comparability of data shared at international level.

Clinical Features of Influenza and Acute Respiratory Illness in Older Adults at Least 50 Years of Age in an Outpatient Setting in the Republic of Korea: a Prospective, Observational, Cohort Study

Two prospective, multi-centre, observational studies (GlaxoSmithKline [GSK] identifier No. 110938 and 112519) were performed over 2 influenza seasons (2007-2008 and 2008-2009) in the Republic of Korea (ROK) with the aim to evaluate the burden of laboratory-confirmed influenza (LCI) in patients ≥ 50 years of age seeking medical attention for acute respiratory illness (ARI). The median participant age was 58 years in the 2007-2008 season and 60 years in the 2008-2009 season. LCI was observed in 101/346 (29.2%) of ARI patients in the 2007-2008 season and in 166/443 (37.5%) of ARI patients in the 2008-2009 season. Compared to patients with non-influenza ARI, those with LCI had higher rates of decreased daily activities (60.4% vs. 32.9% in 2007-2008 and 46.4% vs. 25.8% in 2008-2009), work absenteeism (51.1% vs. 25.6% and 14.4% vs. 7.7%), and longer duration of illness. These results indicated that influenza is an important cause of ARI in adults aged 50 and older causing more severe illness than non-influenza related ARI.

Novel Use of Flu Surveillance Data: Evaluating Potential of Sentinel Populations for Early Detection of Influenza Outbreaks

Influenza causes significant morbidity and mortality each year, with 2-8% of weekly outpatient visits around the United States for influenza-like-illness (ILI) during the peak of the season. Effective use of existing flu surveillance data allows officials to understand and predict current flu outbreaks and can contribute to reductions in influenza morbidity and mortality. Previous work used the 2009-2010 influenza season to investigate the possibility of using existing military and civilian surveillance systems to improve early detection of flu outbreaks. Results suggested that civilian surveillance could help predict outbreak trajectory in local military installations. To further test that hypothesis, we compare pairs of civilian and military outbreaks in seven locations between 2000 and 2013. We find no predictive relationship between outbreak peaks or time series of paired outbreaks. This larger study does not find evidence to support the hypothesis that civilian data can be used as sentinel surveillance for military installations. We additionally investigate the effect of modifying the ILI case definition between the standard Department of Defense definition, a more specific definition proposed in literature, and confirmed Influenza A. We find that case definition heavily impacts results. This study thus highlights the importance of careful selection of case definition, and appropriate consideration of case definition in the interpretation of results.

Clinical predictors for laboratory-confirmed influenza infections: exploring case definitions for influenza-like illness

OBJECTIVE

To identify clinical signs and symptoms (ie, "terms") that accurately predict laboratory-confirmed influenza cases and thereafter generate and evaluate various influenza-like illness (ILI) case definitions for detecting influenza. A secondary objective explored whether surveillance of data beyond the chief complaint improves the accuracy of predicting influenza.

DESIGN

Retrospective, cross-sectional study.

SETTING

Large urban academic medical center hospital.

PARTICIPANTS

A total of 1,581 emergency department (ED) patients who received a nasopharyngeal swab followed by rRT-PCR testing between August 30, 2009, and January 2, 2010, and between November 28, 2010, and March 26, 2011.

METHODS

An electronic surveillance system (GUARDIAN) scanned the entire electronic medical record (EMR) and identified cases containing 29 clinical terms relevant to influenza. Analyses were conducted using logistic regressions, diagnostic odds ratio (DOR), sensitivity, and specificity.

RESULTS

The best predictive model for identifying influenza for all ages consisted of cough (DOR=5.87), fever (DOR=4.49), rhinorrhea (DOR=1.98), and myalgias (DOR=1.44). The 3 best case definitions that included combinations of some or all of these 4 symptoms had comparable performance (ie, sensitivity=89%-92% and specificity=38%-44%). For children <5 years of age, the addition of rhinorrhea to the fever and cough case definition achieved a better balance between sensitivity (85%) and specificity (47%). For the fever and cough ILI case definition, using the entire EMR, GUARDIAN identified 37.1% more influenza cases than it did using only the chief complaint data.

CONCLUSIONS

A simplified case definition of fever and cough may be suitable for implementation for all ages, while inclusion of rhinorrhea may further improve influenza detection for the 0-4-year-old age group. Finally, ILI surveillance based on the entire EMR is recommended.

Influenza and other respiratory viruses detected by influenza-like illness surveillance in Leyte Island, the Philippines, 2010-2013

This study aimed to determine the role of influenza-like illness (ILI) surveillance conducted on Leyte Island, the Philippines, including involvement of other respiratory viruses, from 2010 to 2013. ILI surveillance was conducted from January 2010 to March 2013 with 3 sentinel sites located in Tacloban city, Palo and Tanauan of Leyte Island. ILI was defined as fever ≥38°C or feverish feeling and either cough or running nose in a patient of any age. Influenza virus and other 5 respiratory viruses were searched. A total of 5,550 ILI cases visited the 3 sites and specimens were collected from 2,031 (36.6%) cases. Among the cases sampled, 1,637 (75.6%) were children aged <5 years. 874 (43.0%) cases were positive for at least one of the respiratory viruses tested. Influenza virus and respiratory syncytial virus (RSV) were predominantly detected (both were 25.7%) followed by human rhinovirus (HRV) (17.5%). The age distributions were significantly different between those who were positive for influenza, HRV, and RSV. ILI cases were reported throughout the year and influenza virus was co-detected with those viruses on approximately half of the weeks of study period (RSV in 60.5% and HRV 47.4%). In terms of clinical manifestations, only the rates of headache and sore throat were significantly higher in influenza positive cases than cases positive to other viruses. In conclusion, syndromic ILI surveillance in this area is difficult to detect the start of influenza epidemic without laboratory confirmation which requires huge resources. Age was an important factor that affected positive rates of influenza and other respiratory viruses. Involvement of older age children may be useful to detect influenza more effectively.