Influenza Testing Research Articles

Can telephone data contribute to a national influenza surveillance system in Australia? A retrospective analysis

Introduction: Data collected from telephone helplines that provide health advice can improve the timeliness and accuracy of disease surveillance, contributing to an appropriate and rapid public health response. We show how these data can forewarn health professionals of increased rates of influenza-like illness (ILI) in the community and discuss implications for COVID-19 syndromic surveillance. Methods: The healthdirect helpline (HH) captures demographic details and characteristics of symptoms from users in 6 Australian states and territories. We compare ILI activity in the HH with ILI activity in emergency department (ED), laboratory, Flutracking and general practice (GP) data using cross-correlation functions. Results: Helpline data correlated strongly with ED data (range in yearly correlations from 0.82-0.99), GP data (0.66 – 0.95) and Flutracking data (0.62-0.89), but yearly correlations with laboratory data varied (0.49-0.95). The highest correlation with laboratory and GP data occurred when HH activity was 1-2 weeks in advance of these data, while correlations with ED and Flutracking data were strongest with no time lag. Discussion: Our analysis demonstrates that the number of ILI-related calls to the HH is a reliable indicator of ILI incidence in Australia. An increase in calls is likely to occur simultaneously with an increase in visits to EDs and prior to an increase in positive laboratory influenza tests and visits to GPs. A surveillance system including these data would assist health practitioners to receive timely and accurate estimates of the level of ILI in the community to better respond to and prepare for seasonal and epidemic influenza.

Relative Vaccine Effectiveness of Cell- vs Egg-Based Quadrivalent Influenza Vaccine Against Test-Confirmed Influenza Over 3 Seasons Between 2017 and 2020 in the United States.

Influenza vaccine viruses grown in eggs may acquire egg-adaptive mutations that may reduce antigenic similarity between vaccine and circulating influenza viruses and decrease vaccine effectiveness. We compared cell- and egg-based quadrivalent influenza vaccines (QIVc and QIVe, respectively) for preventing test-confirmed influenza over 3 US influenza seasons (2017-2020). Using a retrospective test-negative design, we estimated the relative vaccine effectiveness (rVE) of QIVc vs QIVe among individuals aged 4 to 64 years who had an acute respiratory or febrile illness and were tested for influenza in routine outpatient care. Exposure, outcome, and covariate data were obtained from electronic health records linked to pharmacy and medical claims. Season-specific rVE was estimated by comparing the odds of testing positive for influenza among QIVc vs QIVe recipients. Models were adjusted for age, sex, geographic region, influenza test date, and additional unbalanced covariates. A doubly robust approach was used combining inverse probability of treatment weights with multivariable regression. The study included 31 824, 33 388, and 34 398 patients in the 2017-2018, 2018-2019, and 2019-2020 seasons, respectively; ∼10% received QIVc and ∼90% received QIVe. QIVc demonstrated superior effectiveness vs QIVe in prevention of test-confirmed influenza: rVEs were 14.8% (95% CI, 7.0%-22.0%) in 2017-2018, 12.5% (95% CI, 4.7%-19.6%) in 2018-2019, and 10.0% (95% CI, 2.7%-16.7%) in 2019-2020. This study demonstrated consistently superior effectiveness of QIVc vs QIVe in preventing test-confirmed influenza over 3 seasons characterized by different circulating viruses and degrees of egg adaptation.

Accuracy of Influenza ICD-10 Diagnosis Codes in Identifying Influenza Illness in Children

Studies of influenza in children commonly rely on coded diagnoses, yet the ability of International Classification of Diseases, Ninth Revision codes to identify influenza in the emergency department (ED) and hospital is highly variable. The accuracy of newer International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) codes to identify influenza in children is unknown. To determine the accuracy of ICD-10 influenza discharge diagnosis codes in the pediatric ED and inpatient settings. Children younger than 18 years presenting to the ED or inpatient settings with fever and/or respiratory symptoms at 7 US pediatric medical centers affiliated with the Centers for Disease Control and Prevention-sponsored New Vaccine Surveillance Network from December 1, 2016, to March 31, 2020, were included in this cohort study. Nasal and/or throat swabs were collected for research molecular testing for influenza, regardless of clinical testing. Data, including ICD-10 discharge diagnoses and clinical testing for influenza, were obtained through medical record review. Data analysis was performed in August 2023. The accuracy of ICD-10-coded discharge diagnoses was characterized using molecular clinical or research laboratory test results as reference. Measures included sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). Estimates were stratified by setting (ED vs inpatient) and age (0-1, 2-4, and 5-17 years). A total of 16 867 children in the ED (median [IQR] age, 2.0 [0.0-4.0] years; 9304 boys [55.2%]) and 17 060 inpatients (median [IQR] age, 1.0 [0.0-4.0] years; 9798 boys [57.4%]) were included. In the ED, ICD-10 influenza diagnoses were highly specific (98.0%; 95% CI, 97.8%-98.3%), with high PPV (88.6%; 95% CI, 88.0%-89.2%) and high NPV (85.9%; 95% CI, 85.3%-86.6%), but sensitivity was lower (48.6%; 95% CI, 47.6%-49.5%). Among inpatients, specificity was 98.2% (95% CI, 98.0%-98.5%), PPV was 82.8% (95% CI, 82.1%-83.5%), sensitivity was 70.7% (95% CI, 69.8%-71.5%), and NPV was 96.5% (95% CI, 96.2%-96.9%). Accuracy of ICD-10 diagnoses varied by patient age, influenza season definition, time between disease onset and testing, and clinical setting. In this large cohort study, influenza ICD-10 discharge diagnoses were highly specific but moderately sensitive in identifying laboratory-confirmed influenza; the accuracy of influenza diagnoses varied by clinical and epidemiological factors. In the ED and inpatient settings, an ICD-10 diagnosis likely represents a true-positive influenza case.

Validity of ICD-10-based algorithms to identify patients with influenza in inpatient and outpatient settings.

To evaluate the validity of ICD-10-CM code-based algorithms as proxies for influenza in inpatient and outpatient settings in the USA. Administrative claims data (2015-2018) from the largest commercial insurer in New Jersey (NJ), USA, were probabilistically linked to outpatient and inpatient electronic health record (EHR) data containing influenza test results from a large NJ health system. The primary claims-based algorithms defined influenza as presence of an ICD-10-CM code for influenza, stratified by setting (inpatient/outpatient) and code position for inpatient encounters. Test characteristics and 95% confidence intervals (CIs) were calculated using test-positive influenza as a reference standard. Test characteristics of alternative outpatient algorithms incorporating CPT/HCPCS testing codes and anti-influenza medication pharmacy claims were also calculated. There were 430 documented influenza test results within the study period (295 inpatient, 135 outpatient). The claims-based influenza definition had a sensitivity of 84.9% (95% CI 72.9%-92.1%), specificity of 96.3% (95% CI 93.1%-98.0%), and PPV of 83.3% (95% CI 71.3%-91.0%) in the inpatient setting, and a sensitivity of 76.7% (95% CI 59.1%-88.2%), specificity of 96.2% (95% CI 90.6%-98.5%), PPV of 85.2% (95% CI 67.5%-94.1%) in the outpatient setting. Primary inpatient discharge diagnoses had a sensitivity of 54.7% (95% CI 41.5%-67.3%), specificity of 99.6% (95% CI 97.7%-99.9%), and PPV of 96.7% (95% CI 83.3%-99.4%). CPT/HCPCS codes and anti-influenza medication claims were present for few outpatient encounters (sensitivity 3%-10%). In a large US healthcare system, inpatient ICD-10-CM codes for influenza, particularly primary inpatient diagnoses, had high predictive value for test-positive influenza. Outpatient ICD-10-CM codes were moderately predictive of test-positive influenza.

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

BackgroundSyndromic 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.MethodsWe 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.ResultsSwabs 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.ConclusionsSymptom 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.

The Role and Value of Professional Rapid Testing of Acute Respiratory Infections (ARIs) in Europe: A Special Focus on the Czech Republic, Poland, and Romania.

This review aims to explore the role of professional diagnostic rapid testing of acute respiratory infections (ARIs), especially COVID-19 and influenza, ensuring proper disease management and treatment in Europe, and particularly in Czech Republic, Poland, and Romania. The paper was constructed based on a review of scientific evidence and national and international policies and recommendations, as well as a process of validation by four experts. The development of new testing technologies, treatment options, and increased awareness of the negative multidimensional impact of ARI profiles transformed differential diagnosis into a tangible and desirable reality. This review covers the following topics: (1) the multidimensional impact of ARIs, (2) ARI rapid diagnostic testing platforms and their value, (3) the policy landscape, (4) challenges and barriers to implementation, and (5) a set of recommendations illustrating a path forward. The findings indicate that rapid diagnostic testing, including at the point of care (POC), can have a positive impact on case management, antimicrobial and antibiotic stewardship, epidemiological surveillance, and decision making. Integrating this strategy will require the commitment of governments and the international and academic communities, especially as we identified room for improvement in the access and expansion of POC rapid testing in the focus countries and the inclusion of rapid testing in relevant policies.

Prospective external validation of the FluScore risk score for influenza in outpatients.

Testing for influenza in patients with acute lower respiratory tract infection (LRTI) is common and in some cases is performed for all patients with LRTI. A more selective approach to testing could be more efficient. We used data from two prospective studies in the US primary and urgent care settings that enrolled patients with acute LRTI or influenza-like illness. Data were collected in the 2016, 2019, 2021, and 2022 flu seasons. All patients underwent polymerase chain reaction (PCR) testing for influenza and the FluScore was calculated based on patient-reported symptoms at their initial visit. The probability of influenza in each risk group was reported, as well as stratum-specific likelihood ratios (SSLRs) for each risk level. The prevalence of influenza within risk groups varied based on overall differences in flu seasons and populations. However, the FluScore exhibited consistent performance across various seasons and populations based on the SSLRs. The FluScore had a consistent SSLR range of 0.20 to 0.23 for the low-risk group, 0.63 to 0.99 for the moderate-risk group, and 1.46 to 1.67 for the high-risk group. The diagnostic odds ratio based on the midpoints of these ranges was 7.25. The FluScore could streamline patient categorization, identifying patients who could be exempted from testing, while identifying candidates for rapid influenza tests. This has the potential to be more efficient than a "one size fits all" test strategy, as it strategically targets the use of tests on patients most likely to benefit. It is potentially usable in a telehealth setting.

Measuring waning protection from seasonal influenza vaccination during nine influenza seasons, Ontario, Canada, 2010/11 to 2018/19.

BackgroundWaning immunity from seasonal influenza vaccination can cause suboptimal protection during peak influenza activity. However, vaccine effectiveness studies assessing waning immunity using vaccinated and unvaccinated individuals are subject to biases.AimWe examined the association between time since vaccination and laboratory-confirmed influenza to assess the change in influenza vaccine protection over time.MethodsUsing linked laboratory and health administrative databases in Ontario, Canada, we identified community-dwelling individuals aged ≥ 6 months who received an influenza vaccine before being tested for influenza by RT-PCR during the 2010/11 to 2018/19 influenza seasons. We estimated the adjusted odds ratio (aOR) for laboratory-confirmed influenza by time since vaccination (categorised into intervals) and for every 28 days.ResultsThere were 53,065 individuals who were vaccinated before testing for influenza, with 10,264 (19%) influenza-positive cases. The odds of influenza increased from 1.05 (95% CI: 0.91-1.22) at 42-69 days after vaccination and peaked at 1.27 (95% CI: 1.04-1.55) at 126-153 days when compared with the reference interval (14-41 days). This corresponded to 1.09-times increased odds of influenza every 28 days (aOR = 1.09; 95% CI: 1.04-1.15). Individuals aged 18-64 years showed the greatest decline in protection against influenza A(H1N1) (aORper 28 days = 1.26; 95% CI: 0.97-1.64), whereas for individuals aged ≥ 65 years, it was against influenza A(H3N2) (aORper 28 days = 1.20; 95% CI: 1.08-1.33). We did not observe evidence of waning vaccine protection for individuals aged < 18 years.ConclusionsInfluenza vaccine protection wanes during an influenza season. Understanding the optimal timing of vaccination could ensure robust protection during seasonal influenza activity.

Excess hospitalizations and in-hospital mortality associated with seasonal influenza in Italy: a 11-year retrospective study

BackgroundInfluenza and flu-like syndromes are difficult to monitor because the symptoms are not specific, laboratory tests are not routinely performed, and diagnosis codes are often lacking or incompletely registered in medical records. This may result in an underestimation of hospital admissions, associated costs, and in-hospital mortality. Therefore, this study aimed to estimate the public health and economic burden of hospitalisations associated with influenza in Italy, at the national and regional levels.MethodsThis 11-year retrospective study included patients admitted to hospitals for influenza or diagnoses associated with influenza (including respiratory and cardiocirculatory conditions) from 2008/09 to 2018/19. Data on hospitalisations were extracted from the Italian Hospital Discharge Records. Information on weekly influenza-like syndrome incidence and weekly average temperature were used to estimate the burden of influenza in terms of hospital admissions in every Italian region and for different age groups by applying a negative binomial model. The model was also applied to estimate in-hospital mortality and the total costs of influenza and influenza-like hospital admissions.ResultsOver the study period, in addition to 3,970 average seasonal admissions coded as influenza, we estimated an average of 21,500 excess hospitalization associated with influenza per season, which corresponds to 36.4 cases per 100,000. Most of the excess hospitalisations concerned older individuals (> 65 years) and children (0–4 years) with 86 and 125 cases per 100,000, respectively. Large variations were observed across regions. Overall, the total estimated hospital burden associated with influenza (including respiratory and cardiocirculatory conditions) was approximately €123 m per year. While the in-hospital mortality for admissions with a primary diagnosis of influenza was very low (~ 150 cases per season), cases increased dramatically for primary diagnoses of influenza and pneumonia (about 9,500 cases per season). The average seasonal in-hospital deaths attributable to influenza were equal to 2,775 cases.ConclusionsOur findings suggest a remarkable underestimation of the burden of influenza, mostly in the older population but not neglectable in younger individuals. Our results may aid the management of current and future flu seasons and should be used for policy making (e.g., vaccine strategies) and operation management choices (e.g., planning and staffing beds during influenza peaks). Overall, the present study supports the need for increased testing for influenza in Italy to tackle the current underestimation of influenza burden.

Surveillance of the respiratory syncytial virus outside infancy: impact of testing methods, a retrospective observational study.

The European Medicines Agency has approved several vaccines to protect the elderly against respiratory syncytial virus (RSV) infections. However, differences in performance between antigen and PCR tests, especially in adults, can make monitoring RSV difficult. This study aims to assess the impact of the chosen diagnostic methods on the surveillance of RSV. RSV and influenza test results obtained from July 2022 to June 2023 in a consolidated clinical laboratory in Brussels, Belgium, were collected. These results included antigen tests, quadruplex PCR tests and viral cultures on respiratory samples. Epidemiological trends related to the age of patients and the diagnostic methods were analysed. Among 14 761 RSV tests, the overall number of positive tests for infants until 1 year of age peaked on 5 November 2022 (67 per 7 days) whereas it peaked on 22 December 2022 for adults (33 per 7 days). Positive antigen tests peaked on 7 November 2022 (56 per 7 days) whereas positive PCRs peaked on 19 December 2022 (36 per 7 days). Nevertheless, the positivity rate of RSV PCRs had peaked 1 month previously. Infants were mainly diagnosed through antigen testing, contrary to older patients. The influenza epidemic was probably the cause of the increased use of a quadruplex PCR, leading to a delayed increase in the absolute number of PCRs positive for RSV. This study shows that the use of different diagnostic methods could lead to an erroneous representation of RSV epidemiology in adults due to the lack of sensitivity of antigen detection. RSV surveillance in the elderly should rely rather on molecular methods.

Comparative analysis of COVID-19 and influenza prevalence among Egyptian pilgrims returning from Hajj and Umrah in 2022: epidemiology, clinical characteristics, and genomic sequencing

PurposeTo describe the changes that occurred in the SARS-CoV-2 and influenza Prevalence, epidemiology, clinical picture, and prevalent genotypes among the Egyptian pilgrims returning from Hajj and Umrah 2022 seasons.MethodsPilgrims were contacted at the airport and invited to participate in the survey. Pilgrims who consented were interviewed using a standardized line list that included participant demographics, respiratory symptoms if any, previous COVID-19 infection, influenza vaccination whereas COVID-19 vaccination information were collected from vaccination cards. Participants were asked to provide throat and nasopharyngeal swabs for SARS-CoV-2 and influenza testing using RT-PCR and a subset of isolates were sequenced. Descriptive data analysis was performed to describe the epidemiology and clinical symptoms of SARS-CoV-2 and influenza. Prevalence rates of SARS-CoV-2 and influenza during Hajj were calculated and compared to Umrah surveys using chi2 and t-test with a significance level < 0.05.ResultsOverall, 3,862 Egyptian pilgrims enrolled, their mean age was 50.5 ± 47 years, half of them were > 50 years of age and 58.2% were males. Of them, 384 (9.9%) tested positive for SARS-CoV-2 and 51 (1.3%) for influenza viruses. Prevalence of SARS-CoV-2 infections (vaccine breakthrough) increased significantly between the Umrah and Hajj surveys (6.7% vs. 9.9%, p < 0.001), and variants of the virus varied considerably. Whereas no significant difference was found in influenza prevalence, vaccine coverage and vaccine breakthrough infection rates (11.7 vs. 9.2%, 26.9 vs. 26.8%, and 1.4 vs. 1.1% respectively).ConclusionsSARS-CoV-2 prevalence among Egyptian pilgrims returning from Hajj in July increased with reduced vaccine effectiveness compared to Umrah in March 2022 suggesting a possible wave of SARS-CoV-2 in the upcoming winter.

The Polk COVID-19 and Flu Response clinical trial: COVID-19 antibody positivity higher in Black EMS workers

This study reports on a countywide assessment of COVID-19 positivity among emergency medical services workers. Participants completed a short survey of demographic factors and co-morbidities prior to obtaining COVID-19 and influenza testing to analyze the prevalence of these two respiratory viruses that EMS workers, being the first on the scene, are at special risk for, especially in the early days of the pandemic. A total of 7% had a positive COVID-19 antibody test. Although Black EMS personnel only comprised 9% of the cohort, they were significantly more likely to test positive for COVID-19 (P=0.0012). Black race remained a statistically significant predictor in a multivariate model that included the age, sex, BMI, number of hours of direct patient contact, whether the medic was symptomatic, presence of co-morbidities and whether or not the medic had received a flu shot prior (P=0.0008, 95% CI 0.0621-0.2354). This clinical trial (NCT04682132) ) was registered at clinicaltrials.gov, a resource provided by the U.S. National Library of Medicine.

Surveillance of seasonal influenza viruses during the COVID-19 pandemic in Tokyo, Japan, 2018-2023, a single-center study.

COVID-19 pandemic led to significant reductions in influenza detection worldwide, fueling debates on whether influenza truly ceased circulating in communities. The number of influenza cases decreased significantly in Japan, raising concerns about the potential risk of decreased immunity to influenza in the population. Our single-center study aimed to investigate influenza trends before and during the COVID-19 pandemic in Tokyo, Japan. This cross-sectional study included patients of all ages who visited Tokyo Shinagawa Hospital between April 1, 2018, and March 31, 2023. Influenza and COVID-19 tests were conducted using Quick Navi-Flu2 and polymerase chain reaction (PCR). We analyzed data from before and during the COVID-19 epidemic, based on patient background, hospitalization, and deaths, collected from medical records. A total of 12 577 influenza tests were conducted, with approximately 100 tests consistently performed each month even in the influenza off-season. Throughout the observation period, 962 positive cases were identified. However, no cases were observed for 27 months between March 2020 and November 2022. Influenza A cases were reobserved in December 2022, followed by influenza B cases in March 2023, similar to the influenza incidence reports from Tokyo. The positivity rate during the 2022-2023 winter season was lower than before the COVID-19 epidemic and decreased in elderly patients, with no hospitalizations or deaths observed. This single-center study provided actual trend data for influenza patients before and during COVID-19 outbreaks in Tokyo, which could offer insights into the potential impact and likelihood of influenza virus infection in Japan.

Differentiating COVID-19 and influenza in children: hemogram parameters as diagnostic tools.

It is not always possible to differentiate between influenza and COVID-19 based on symptoms alone. This is a topic of significant importance as it aims to determine whether there are specific hematological parameters that can be used to distinguish between influenza and COVID-19 in children. Two hundred thirty-one children between the ages of 1 month and 18 years who presented to the children's outpatient clinic between June 2021 and June 2022 with similar symptoms and were tested with an influenza test and a COVID-19 PCR test were included in the study. Of the patients included in the study, 130 tested positive for COVID-19 and 101 positive for influenza. The patients were evaluated for hematological parameters. Age, eosinophils and monocyte factors were shown to be statistically significantly effective in COVID-19. The risk of COVID-19 increased 1,484-fold with age, 10,708-fold with increasing eosinophil count, and 1,591-fold with increasing monocyte count. The performance of the monocyte count and eosinophil count was assessed by receiver operating characteristic curve (ROC) analysis. According to the performed ROC analysis, the area under the curve (AUC) value was observed to be 0.990 for monocytes. According to the cutoff point >1.50, the sensitivity value was determined as 98.4% and the specificity value as 97.0%. AUC significance for eosinophils was found to be 0.989. According to the cutoff point >0.02, the sensitivity value was determined as 99.2% and the specificity value as 93.1%. In the diagnosis of COVID-19, the eosinophil count and monocyte count are easily accessible, inexpensive, and important parameters in terms of differential diagnosis and can help in the differentiation of COVID-19 from influenza during seasonal outbreaks of the latter. Developing parameters for clinicians to use in diagnosing COVID-19 and influenza can facilitate their work in practice.

Influence of COVID-19 over seasonal influenza activity in southern India

Basic epidemiological data is urgently needed in order to ascertain the changes brought about by COVID-19 pandemic, and help researchers, clinicians, and policy makers in addressing these issues. Data on influenza positivity from 2009 to 2019 was collected from Regional Influenza laboratory, JIPMER. Being COVID testing centre we tested samples (2020–2023) from Tamilnadu and Pondicherry. All SARI samples which were negative for COVID-19 were subjected to Influenza testing as regular surveillance activity was suspended. On comparison we found significant reduction in detection rates of influenza A H1N1, H3N2 and influenza B (p value = <0.01).

Prevalence and trends in mono- and co-infection of COVID-19, influenza A/B, and respiratory syncytial virus, January 2018-June 2023.

This study aimed to determine the impact of the COVID-19 pandemic on the overall prevalence and co-infection rates for COVID-19, influenza A/B, and respiratory syncytial virus in a large national population. We conducted a retrospective review of 1,318,118 multi-component nucleic acid amplification tests for COVID-19, influenza A/B, and RSV performed at Labcorp® sites from January 2018 to June 2023, comparing positivity rates and co-infection rates by age, sex, and seasonality. In 2021-2023, 1,232 (0.10%) tested positive for COVID-19 and influenza A/B, 366 (0.03%) tested positive for COVID-19 and RSV, 874 (0.07%) tested for influenza A/B and RSV, and 13 (0.001%) tested positive for COVID-19, influenza A/B, and RSV. RSV positivity rates were particularly higher in Q2 and Q3 of 2021 and in Q3 of 2022. Higher influenza A positivity proportions were found in Q4 of 2021 and again in Q2 and Q4 of 2022. Influenza B positivity had been minimal since the start of the pandemic, with a slight increase observed in Q2 of 2023. Our findings highlight the need for adaptability in preparation for upper respiratory infection occurrences throughout the year as we adjust to the COVID-19 pandemic due to the observed changes in the seasonality of influenza and RSV. Our results highlight low co-infection rates and suggest heightened concerns for co-infections during peaks of COVID-19, influenza, and RSV, which may perhaps be reduced.

Characteristics and outcomes of patients hospitalized for infection with influenza, SARS-CoV-2 or respiratory syncytial virus in the season 2022/2023 in a large German primary care centre

BackgroundIn 2022/2023, Influenza A and Respiratory Syncytial Virus (RSV) reappeared in hospitalized patients, which was in parallel to ongoing SARS-CoV-2 infections. The aim of our study was to compare the characteristics and outcomes of these infections during the same time.MethodsWe included patients of all ages with a positive polymerase chain reaction (PCR) test for Influenza A/B, RSV, or SARS-CoV-2 virus hospitalized in the neurological, internal or paediatric units of the RoMed Hospital Rosenheim, Germany, between October 1st 2022 and February 28th 2023.ResultsA total of 906 patients were included (45.6% female; median age 68.0 years; 21.9% Influenza A, 48.2% SARS-CoV-2, 28.3% RSV). Influenza B (0.2%) and co-infections (1.5%) played a minor role. In patients aged ≥ 18 years (n = 637, 71%), Influenza A, SARS-CoV-2 and RSV groups differed in age (median 72, 79, 76 years, respectively; p < 0.001). Comorbidities, particularly asthma and COPD, were most prevalent for RSV. 103 patients were admitted to the intensive care unit (ICU) (16.3% Influenza A, 15.3% SARS-CoV-2, 19.2% RSV; p = 0.649), 56 died (6.8% Influenza A, 9% SARS-CoV-2, 11.1% RSV; p = 0.496). RSV showed the highest frequencies of low-flow oxygen supplementation for admission and stay. Differences in the length of stay were minor (median 7 days). Conversely, in patients aged < 18 years (n = 261, 28,8%), 19.5%, 17.6% and 60.2% were in the Influenza A, SARS-CoV-2 and RSV groups, respectively; 0.4% showed Influenza B and 2.3% co-infections. 17 patients were admitted to ICU (3.9% Influenza A, 9.6% RSV, 0% SARS-CoV-2); none died. RSV showed the highest frequencies of high- and low-flow oxygen supplementation, SARS-CoV-2 the lowest.ConclusionWhen comparing infections with Influenza, SARS-CoV-2 and RSV in the winter 2022/2023 in hospitalized adult patients, rates of ICU admission and mortality were similar. RSV showed the highest frequencies of obstructive airway diseases, and of oxygen supplementation. The latter was also true in children/adolescents, in whom RSV dominated. Thus, in the situation of declining importance of SARS-CoV-2, RSV showed a disease burden that was relatively higher than that from Influenza and SARS-CoV-2 across ages, and this might be relevant for the seasons coming.

Influenza Vaccine Effectiveness Against Influenza A-Associated Emergency Department, Urgent Care, and Hospitalization Encounters Among US Adults, 2022-2023.

The 2022-2023 United States influenza season had unusually early influenza activity with high hospitalization rates. Vaccine-matched A(H3N2) viruses predominated, with lower levels of A(H1N1)pdm09 activity also observed. Using the test-negative design, we evaluated influenza vaccine effectiveness (VE) during the 2022-2023 season against influenza A-associated emergency department/urgent care (ED/UC) visits and hospitalizations from October 2022 to March 2023 among adults (aged ≥18 years) with acute respiratory illness (ARI). VE was estimated by comparing odds of seasonal influenza vaccination among case-patients (influenza A test positive by molecular assay) and controls (influenza test negative), applying inverse-propensity-to-be-vaccinated weights. The analysis included 85 389 ED/UC ARI encounters (17.0% influenza A positive; 37.8% vaccinated overall) and 19 751 hospitalizations (9.5% influenza A positive; 52.8% vaccinated overall). VE against influenza A-associated ED/UC encounters was 44% (95% confidence interval [CI], 40%-47%) overall and 45% and 41% among adults aged 18-64 and ≥65 years, respectively. VE against influenza A-associated hospitalizations was 35% (95% CI, 27%-43%) overall and 23% and 41% among adults aged 18-64 and ≥65 years, respectively. VE was moderate during the 2022-2023 influenza season, a season characterized with increased burden of influenza and co-circulation with other respiratory viruses. Vaccination is likely to substantially reduce morbidity, mortality, and strain on healthcare resources.

898. Influenza Surveillance in the US Veterans Health Administration (VHA): 2022-2023 Season

Abstract Background Influenza causes seasonal epidemics with substantial morbidity and mortality. Veterans Health Administration’s (VHA) large elderly population is at higher risk for influenza complications, including hospitalization, and death. Herein we summarize VHA’s national annual surveillance data for influenza activity and vaccinations. Methods Influenza-like-illness (ILI) as well as influenza-coded outpatient visits and hospitalizations, laboratory testing, and antivirals were obtained from VHA data sources (10/2/2022-4/22/23) and compared to prior years and CDC data. Vaccinations were captured starting 8/1/2022, with rates calculated based on VHA users in each fiscal year. Influenza RT-PCR positive respiratory samples underwent whole genome sequencing (WGS) to analyze clade and antiviral resistance. Results Surveillance metrics are presented (Table). Vaccinations were decreased compared to 2021-22, but the used of adjuvanted vaccine was increased. Weekly ILI ranged from 0.4%-1.4% in primary/urgent care settings. Activity was highest for 2022 Week 48, matching national influenza trends (Fig.1). Testing found 23,297 influenza positives of 457,020 tests performed (5.1%). Median length of stay (3 days) for hospitalized patients and deaths (127, 3%) were stable. Among 115 deaths where influenza type was available, 110 had Influenza A and 5 Influenza B. Following two low activity seasons, total influenza positives, outpatient visits, and hospitalizations during 2022-23 tracked closer to seasons prior to the COVID-19 pandemic (Table, Fig.2). 411 samples (in 16 states) were sequenced (410 Flu A: 136 H1, 274 H3; 1 B/Victoria), representing 12 subclades, which aligned with CDC reporting. No drug resistance mutations were found (Fig.3). Conclusion For 2022-23, influenza vaccinations in VHA dropped but percent vaccinated was stable. For the first time, over half of VHA-administered vaccines were adjuvanted formulation. The influenza season was notable for an earlier than usual peak (late Nov/early Dec), with overall increased activity compared to the prior two seasons. Testing for influenza during 2022-23 season was decreased but remained higher than pre-COVID-19 pandemic testing levels. VHA influenza activity and WGS analysis tracks closely with national CDC reporting. Disclosures All Authors: No reported disclosures

2475. Admissions Screening for Influenza and RSV Among a Highly Immunosuppressed Patient Population

Abstract Background During the Fall/Winter 2022-23, the U.S. experienced an early surge of Influenza and RSV cases, while SARS-CoV-2 cases persisted. With concerns of a potential “tripledemic” on the horizon, the NIH Clinical Center, a clinical research hospital with a heavily immunosuppressed patient population, implemented Influenza and RSV testing, in addition to SARS-CoV-2, for all patients on admission to facilitate early detection and prompt isolation of infected patients. Methods Nasopharyngeal (NP) swabs (n=1213) were collected on admission from 11/2022 to 4/2023 and tested for Influenza and RSV by PCR. 1213 NP swabs from 985 unique patients were tested (some patients had multiple admissions); 1100 were tested on the Panther Fusion® SARS-CoV-2 Assay (Hologic, Inc.) and 113 using the SARS-CoV-2 RT-PCR Xpert® Xpress test. Medical chart reviews and discussions with patient care providers elucidated whether cases identified on admission were asymptomatic. Results Of 1213 NP swabs collected from patients admitted to our hospital, 5 (0.41%) were identified with Influenza A infection, 4 (0.33%) RSV infection and no patients were identified with Influenza B. Two (0.16%) had a known history of RSV infection, 3 (0.25%) screened negative for symptoms but subsequently disclosed symptoms, 1 (0.08%) was asymptomatic on admission but disclosed a recent history of an upper respiratory infection, and 3 were asymptomatic. All infections were detected between late November 2022 to mid-January 2023, when community transmission was high, yielding a 2-month positivity rate of 2.3% during this time of peak community spread. Conclusion Admission surveillance for Influenza and RSV during a respiratory virus surge in our community allowed us to isolate nine patients on admission who would likely not have been appropriately isolated, as symptom screening alone is not reliable. Surveillance is important to be able to identify infected patients promptly when respiratory infections are rampant in the community, and especially for institutions serving immunosuppressed patients. Disclosures All Authors: No reported disclosures