Abstract
Abstract
Objective
Respiratory syncytial virus (RSV) is an important viral pathogen in children, older adults and adults with certain high-risk conditions. In our prospective community-based cohort study of adults 50 years and older before the COVID-19 pandemic, the incidence of RSV acute respiratory infection (ARI) was 48.6 cases/1000 person-years (PY), which decreased to near zero during the COVID-19 pandemic. Our objective was to determine the incidence of RSV-ARI during the 2 years following the initial phase of the pandemic (2021–2022 and 2022–2023).
Design
This is a community-based prospective cohort study.
Setting
Adults living in southeast Minnesota from October 2021 to September 2022 (year 3) and October 2022 to September 2023 (year 4).
Participants
Adults≥50 years (n=2500).
Primary and secondary outcomes
We calculated incidence and attack rates for RSV-ARI as primary outcome and reported hospitalisations, pneumonia and death following ARI as secondary outcome.
Results
There were 2500 participants in the study with a mean age of 68.2 years (SD 9.3) at the start of year 3. Participants were predominantly female (60%), non-Hispanic white (96%) and residing in urban areas (76%). The incidence rate of RSV-ARI was 6.12/1000 PY (95% CI 3.42 to 10.09) in 2021–2022 and 16.40/1000 PY (95% CI 11.66 to 22.42) in 2022–2023. We noted higher attack rates of RSV-ARI during the winter months. There were no hospitalisations, pneumonia or deaths within 30 days of RSV-ARI.
Conclusions
Compared with the period before the COVID-19 pandemic, RSV-ARI incidence was lower in both 2021–2022 and 2022–2023 periods. In 2022–2023, the incidence increased 2.7-fold compared with the 2021–2022 period. The observed incidence rates, particularly the significant increase in the most recent season, underscore the continued public health relevance of RSV-ARI and support the rationale for ongoing RSV vaccination efforts to mitigate its overall burden in the population.
Keywords: Respiratory infections, GERIATRIC MEDICINE, Community-Based Participatory Research
STRENGTHS AND LIMITATIONS OF THIS STUDY.
Community-based, prospective cohort study of adults over 50.
PCR-verified infection over two respiratory seasons.
Prospective follow-up for healthcare utilisation and severe outcomes such as hospitalisation, pneumonia and death in adults ≥50 years.
Single geographical location, use of single-collection PCR testing.
Individuals with active COVID-19 infection were not tested for respiratory syncytial virus (RSV), leading to potential underestimation of RSV incidence.
Background
Respiratory syncytial virus (RSV) is an important cause of acute respiratory infection (ARI) in infants,1 older adults and adults with certain high-risk conditions.2–4 A community-based study from 1999 to 2003 found RSV annual incidence rate of 3–7% in healthy older adults aged ≥65 years, and 4–10% in adults aged ≥21 years with cardiac or pulmonary illnesses using nasal swabs with PCR collected by research personnel.5 The COVID-19 pandemic changed the incidence rates dramatically for all ARIs after initiation of public health measures.6 A decline in RSV infections was reported during the initial phase of the COVID-19 pandemic in 2020.7 However, RSV activity later rebounded,8 and the activity shifted in RSV epidemiology6 in patients coming to medical attention. Most research to date has focused on medically attended RSV, highlighting a gap in understanding community-level incidence, which is crucial for informing public health policy.
Our study measured RSV incidence and its seasonal patterns after lifting of the public health measures (wearing masks, social distancing) following the COVID-19 pandemic9 in community-based adults aged 50 years and older. This study represents the final period prior to the use of RSV vaccines.3 RSV vaccines were first approved in the USA in May 2023 by the Food and Drug Administration (FDA) for the prevention of RSV lower respiratory tract disease (LRTD) for use in adults aged ≥60 years.3 In 2024, the FDA also approved RSV vaccines for adults aged 50–59 at increased risk for RSV disease.10 The RSV vaccines are currently recommended for all adults aged ≥75 years and adults aged 60–74 at increased risk for severe RSV disease (eg, adults with chronic cardiovascular disease, chronic lung or respiratory disease, chronic liver disease, chronic haematologic conditions, severe obesity, moderate or severe immune compromise, residence in a nursing home, etc).4 Our primary aim was to estimate the incidence of RSV in adults ≥50 years during two consecutive years, October 2021–September 2022 and October 2022–September 2023. The public health importance of understanding RSV incidence following the COVID-19 pandemic is substantial, and these findings may impact epidemiological work on future epidemics.11
Methods
Study design, cohort description, recruitment and procedures
This is an analysis for years 3 (October 2021–September 2022) and 4 (October 2022–September 2023) of a 4-year prospective cohort study, for which we previously reported the incidence of RSV-ARI during the first 2 years of the study (October 2019–September 2021).12 The original cohort and the study design are detailed elsewhere.12 Briefly, we conducted a prospective cohort study of community-dwelling participants 50 years and older living in southeastern Minnesota. We originally consented 2325 subjects in 2019 to participate for two consecutive RSV seasons,12 but with the onset of the COVID-19 pandemic, we extended the study during the non-RSV seasons (starting 1 May 2021) and followed subjects who reconsented for an additional 2.5 years (until 30 September 2023).13 We supplemented those who chose not to reconsent by inviting a new cohort of subjects to participate in the last 2 years (1 October 2021–30 September 2023) of the study.13 We used virtual recruitment strategies described previously.14 The inclusion criteria included the following: aged 50 years and above, living and receiving medical care within southeast Minnesota and a willingness to perform a self-collected nasal swab at home for subsequent lab-based RSV PCR testing.12 This differed compared with our previous report when patients did either self-swab or clinic swab; however, concordance between methods is generally about 90%.15 All participants used a primary care provider at Mayo Clinic (Rochester, Minnesota, USA) and received medical care in southeastern Minnesota. All participants provided written consent as well as authorisation for medical record review in accordance with Minnesota state statute 144.290-144.298.16
Participants were excluded if they did not meet age, residency or medical provider criteria or if they refused study procedures like nasal swabs. Participants were excluded from the initial cohort if they developed an ARI after 1 October 2019 and before their consent date. Participants were excluded if they were out of the study region for more than 2 weeks during the RSV season (October–April) or over 4 weeks during the non-RSV season (May–September) to ensure they could provide a self-swab when they developed ARI symptoms. Participants were also excluded if they were unable to ambulate, had cognitive impairment or if the investigators felt the participant could not complete the requirements of the study or had concerns for safety. These exclusions were added to ensure adequate compliance with swabs and ability to test frailty. We adhered to the STrengthening the Reporting of OBservational studies in Epidemiology (STROBE) guidelines for cohort studies.17 We conducted the study within the principles of the Declaration of Helsinki.18
Patient and public involvement
None.
Measurement of variables
The primary outcome was the development of RSV-ARI. The definition of ARI has been described previously.12 ARI was defined as two or more upper respiratory tract symptoms or at least two signs/symptoms from different locations (upper, lower or systemic) for at least 24 hours (online supplemental table 1). LRTD was defined as at least two lower respiratory signs/symptoms for at least 24 hours or reduction in oxygen saturation (online supplemental table 1). Participants with ARI were placed in severity categories of mild, moderate and severe. Patients with mild ARI had upper respiratory tract infection symptoms only, without fever or systemic signs/symptoms. Moderate ARI involved systemic symptoms of infection with upper respiratory tract symptoms or symptoms requiring outpatient visits. Severe illness involved systemic symptoms of infection with lower respiratory symptoms or symptoms requiring emergency department visit or hospitalisation. When participants developed symptoms of ARI, they communicated with study staff to determine if their symptoms met ARI criteria. To minimise under-ascertainment by a lack of self-report, we conducted surveillance via the electronic medical record and communicated with participants if they had potential symptoms in the record. If they met the criteria, they were instructed to self-collect a nasal swab, as previously described,12 as long as they were not known to have COVID-19 (this was enacted during the early phase of pandemic to protect staff who interacted with the sample and continued throughout study). If patients were determined to have COVID-19, those patients did not swab for RSV and were considered missing for RSV. Self-collected specimens were tested for RSV using FDA-approved reverse transcription-PCR (RT-PCR) assays (Simplexa Flu A/B and RSV Direct, DiaSorin Molecular, Cypress CA; Panther Fusion Flu A/B and RSV Assay, Hologic). This PCR also tested for influenza A/B infection.
We measured healthcare utilisation by outpatient visits, emergency department visits, hospitalisation, hospital length of stay and hospitalisation with intensive care unit (ICU) stay following respiratory infection within 4 weeks of ARI. We performed this analysis for hypothesis generation. We reported the ARI complications, including pneumonia, hospitalisation or death within 4 weeks of ARI. We obtained these healthcare outcomes by manual chart review of their visits to determine if the visit was related to their symptoms. Pneumonia was a clinical diagnosis as noted from chart abstraction for evaluation of outcomes. Mortality following ARI was determined using the electronic health record from previously described methods.19
We reported demographics of age, self-reported gender, race and ethnicity, using the electronic health record (EHR). Age was categorised into 10-year age groups, and gender reported as female or male (n and percentage). We reported race and ethnicity as non-Hispanic white, Hispanic or Latino, African American, American Indian/Alaskan Native, Asian and unknown. We classified living environment as rural, urban or missing (as defined by the US Census Bureau) by using their permanent address.20
We reported the history of congestive heart failure, asthma, chronic obstructive pulmonary disease and diabetes mellitus within 3 years from the start of year 3. For socioeconomic status (SES), we reported the HOUsing-based SocioEconomic Status (HOUSES) index in quartiles. The HOUSES index accounts for the characteristics of the home which includes four real property variables including the assessor’s value, housing square footage, number of bedrooms and bathrooms in the home.21 A low HOUSES quartile score indicates a lower SES and has been associated with adverse health outcomes in older adults.22
Data analysis procedure
We analysed and reported RSV-ARI during and through the end of the COVID-19 omicron period of the pandemic. We divided the study period into 2 years, year 3 (1 October 2021–30 September 2022) and year 4 (1 October 2022–30 September 2023) and further divided each year into the RSV season (1 October –30 April) and non-RSV season (1 May–30 September). We expressed the incidence rate as the number of first RSV-positive respiratory cases per 1000 person-years (PY) with exact Poisson 95% CIs. To calculate PY, the beginning of follow-up was the date of the start of the time period (ie, given year). The end of the follow-up was the date of the end of the time period, the symptom onset of RSV-positive ARI (if occurred during the period) or last follow-up (moving out of region, death, discontinuation of the study) whichever came first. We expressed the attack rate as the percentage of participants with at least one RSV-positive ARI during the period with Clopper–Pearson Exact 95% CIs. We also included incidence rates standardised to the US population with white race by age and sex using the 2020 US Census with 95% CI using the normal approximation. We used this standardisation as it best represented the population in the study. Presence of complications and healthcare utilisations related to ARI are reported at the ARI episode level as count (percentage). Missing data of participant characteristics and RSV test results (often due to COVID-19 positivity) were summarised descriptively. SAS statistical software was used to conduct the analyses (V.9.4M7; SAS Institute Cary, North Carolina, USA), and R statistical software was used to generate the figures with ggplot (V.4.2.2; Vienna, Austria).
Results
Study participants
In years 3 and 4 of follow-up, 2511 participants consented or reconsented; however, 11 of them were withdrawn prior to the start of year 3 ARI surveillance (1 October 2021)14 (figure 1 for cohort development). We reported participants as either reconsented or newly consented (online supplemental table 2). The mean age of participants at start of year 3 was 68.2 years (SD 9.3), 60.1% were female, 96.4% identified as non-Hispanic white and 12.9% had diabetes, 10.7% asthma, 6.7% chronic obstructive pulmonary disease and 4.8% congestive heart failure (table 1). The majority (64.6%) of the cohort had received COVID-19 vaccination and 44.6% had received influenza vaccination in the 1 year prior. RSV vaccination started at the end of the fourth non-RSV season with FDA approval in May 2023 and initial Advisory Committee on Immunization Practices recommendation for RSV on 21 June 2023. Only 66 participants were vaccinated (median 11.5 days prior to the end of study period; total 2.37 PY of total follow-up after vaccination across all subjects). Among ARI episodes during years 3 and 4, 574 (25%) were missing RSV status due to lack of RSV swab specimen. The majority (70%) of these ARI episodes without RSV status were positive for COVID-19 which was the reason for not performing the home nasal swab.
Figure 1. Cohort development. IE refers to inclusion and exclusion. Health decline refers to when participants developed new or worsening health conditions that preventedthem from participating in the study.
Table 1. Sociodemographic at start of year 3 and clinical characteristics by RSV status (analysis set for year 3).
| Patients with at least one RSV-ARI (N=54) | Patients with non-RSV-ARI (N=759) | Patients with missing RSV-ARI status (N=517) | Patients without ARI (N=1170) | Total (N=2500) |
|
|---|---|---|---|---|---|
| Age in years at start of year 3 | |||||
| Mean (SD) | 65.4 (7.8) | 67.5 (8.9) | 67.9 (8.6) | 68.9 (9.9) | 68.2 (9.3) |
| Median (range) | 65 (53–86) | 67 (50–96) | 67 (50–94) | 68 (50–98) | 67 (50–98) |
| Age category at start of year 3, n (%) | |||||
| 50–59 years | 11 (20.4%) | 150 (19.8%) | 79 (15.3%) | 208 (17.8%) | 448 (17.9%) |
| 60–69 years | 31 (57.4%) | 307 (40.4%) | 226 (43.7%) | 446 (38.1%) | 1010 (40.4%) |
| 70–79 years | 8 (14.8%) | 224 (29.5%) | 161 (31.1%) | 317 (27.1%) | 710 (28.4%) |
| 80 years or older | 4 (7.4%) | 78 (10.3%) | 51 (9.9%) | 199 (17.0%) | 332 (13.3%) |
| Gender, n (%) | |||||
| Female | 41 (75.9%) | 484 (63.8%) | 289 (55.9%) | 689 (58.9%) | 1503 (60.1%) |
| Race/ethnicity, n (%) | |||||
| American Indian/Alaskan Native | 0 (0.0%) | 2 (0.3%) | 1 (0.2%) | 1 (0.1%) | 4 (0.2%) |
| Asian | 0 (0.0%) | 5 (0.7%) | 1 (0.2%) | 17 (1.5%) | 23 (0.9%) |
| African American | 0 (0.0%) | 3 (0.4%) | 4 (0.8%) | 9 (0.8%) | 16 (0.6%) |
| Hispanic or Latino | 0 (0.0%) | 6 (0.8%) | 3 (0.6%) | 6 (0.5%) | 15 (0.6%) |
| Unknown | 0 (0.0%) | 10 (1.3%) | 9 (1.7%) | 12 (1.0%) | 31 (1.2%) |
| Non-Hispanic white | 54 (100.0%) | 733 (96.6%) | 499 (96.5%) | 1125 (96.2%) | 2411 (96.4%) |
| Rurality, n (%) | |||||
| Living in rural area | 11 (20.4%) | 205 (27.2%) | 113 (21.9%) | 267 (22.9%) | 596 (24.0%) |
| Living in urban area | 43 (79.6%) | 549 (72.8%) | 403 (78.1%) | 897 (77.1%) | 1892 (76.0%) |
| Missing | 0 | 5 | 1 | 6 | 12 |
| SES (HOUSES in quartile), n (%) | |||||
| Q1 (lowest SES) | 5 (9.6%) | 76 (10.6%) | 61 (12.3%) | 172 (15.6%) | 314 (13.3%) |
| Q2 | 8 (15.4%) | 183 (25.6%) | 121 (24.3%) | 275 (24.9%) | 587 (24.8%) |
| Q3 | 21 (40.4%) | 199 (27.8%) | 153 (30.8%) | 323 (29.3%) | 696 (29.4%) |
| Q4 (highest SES) | 18 (34.6%) | 257 (35.9%) | 162 (32.6%) | 334 (30.3%) | 771 (32.6%) |
| Missing | 2 | 44 | 20 | 66 | 132 |
| Chronic illness (within 3 year of start of year 3), n (%) | 31 (57.4%) | 473 (62.3%) | 353 (68.3%) | 753 (64.4%) | 1610 (64.4%) |
| Congestive heart failure, n (%) | 1 (1.9%) | 34 (4.5%) | 24 (4.6%) | 62 (5.3%) | 121 (4.8%) |
| Asthma, n (%) | 10 (18.5%) | 92 (12.1%) | 63 (12.2%) | 103 (8.8%) | 268 (10.7%) |
| Chronic obstructive pulmonary disease, n (%) | 5 (9.3%) | 43 (5.7%) | 41 (7.9%) | 79 (6.8%) | 168 (6.7%) |
| Diabetes mellitus, n (%) | 5 (9.3%) | 95 (12.5%) | 68 (13.2%) | 154 (13.2%) | 322 (12.9%) |
| Previous vaccination before start of year 3 | |||||
| Influenza vaccination (within 1 year), n (%) | 25 (46.3%) | 360 (47.4%) | 240 (46.4%) | 490 (41.9%) | 1115 (44.6%) |
| COVID-19 vaccination (within 1 year), n (%) | 41 (75.9%) | 502 (66.1%) | 319 (61.7%) | 752 (64.3%) | 1614 (64.6%) |
| Pneumococcal vaccination (ever), n (%) | 23 (42.6%) | 407 (53.6%) | 303 (58.6%) | 647 (55.3%) | 1380 (55.2%) |
| Time since the latest pneumococcal vaccination, years | |||||
| Mean (SD) | 3.2 (2.9) | 3.5 (2.6) | 3.5 (2.9) | 3.9 (2.9) | 3.7 (2.8) |
| Median (range) | 2 (0–13) | 3 (0–17) | 3 (0–21) | 4 (0–20) | 4 (0–21) |
| History of RSV infection ever before start of year 3, n (%) | 0 (0.0%) | 23 (3.0%) | 12 (2.3%) | 24 (2.1%) | 59 (2.4%) |
ARI, acute respiratory infection; HOUSES, HOUsing-based SocioEconomic Status; Missing RSV-ARI, patients with missing and/or invalid RT-PCR RSV results for at least one ARI episode (often because of COVID-19 positivity) and without any RT-PCR RSV-positive ARI episode; N, number of subjects; Non-RSV-ARI, patients with RT-PCR RSV-negative results for all ARI episodes during years 3 and 4; RSV, respiratory syncytial virus; RSV-ARI, patients with at least one RT-PCR RSV-positive ARI episode during years 3 and 4; SES, socioeconomic status; Without ARI, patients with no ARI episodes during years 3 and 4.
Incidence and attack rate of RSV-positive ARI
During 2021–2022 following the initial phase of the COVID-19 pandemic in 2020, we found a total of 15 RSV-ARI cases from 2500 participants (attack rate 0.60% (95% CI 0.34 to 0.99)), 14 of which occurred during the RSV season and 1 at the end of the non-RSV season. We found a crude incidence rate of 6.12/1000 PY (95% CI 3.42 to 10.09) and a standardised age-gender-adjusted incidence rate of 6.17 cases/1000 PY (95% CI 2.57 to 9.76). When stratified by age, we found an RSV-ARI incidence rate of 6.84 cases/1000 PY (95% CI 1.41 to 19.98) and an attack rate of 0.67% (95% CI 0.14 to 1.94) in adults aged 50–59 years. In adults aged 60 years and older, there was an RSV-ARI incidence rate of 5.96 cases/1000 PY (95% CI 3.08 to 10.41) and an attack rate during this time was 0.59% (95% CI 0.30 to 1.02). Further stratification by gender showed similar RSV-ARI incidence rates. The majority of the RSV-ARIs were reported as severe because of lower respiratory tract symptoms (table 2). For the incidence of RSV-LRTD, we found an age-gender standardised incidence of 2.79/1000 PY (95% CI 0.05 to 5.53) in year 3 and 8.90/1000 PY (95% CI 4.26 to 13.53) in year 4 (online supplemental table 3).
Table 2. Incidence rate (per 1000 person-years) of first episode of RSV-ARI by age category, gender, RSV subtyping and severity and their attack rates for years 3 and 4.
| Year 3: 1 October 2021–30 September 2022 | Year 4: 1 October 2022–30 September 2023 | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Incidence rate | Attack rate | Incidence rate | Attack rate | |||||||||
| N | n | Value | 95% CI | Value | 95% CI | N | n | Value | 95% CI | Value | 95% CI | |
| Overall | ||||||||||||
| Unstandardised | 2500 | 15 | 6.12 | 3.42 to 10.09 | 0.6 | 0.34 to 0.99 | 2446 | 39 | 16.4 | 11.66 to 22.42 | 1.59 | 1.14 to 2.17 |
| Standardised age-gender-adjusted incidence rate (based on 2020 US white population) | – | – | 6.17 | 2.57 to 9.76† | – | – | – | – | 16.99 | 10.63 to 23.35† | – | – |
| Age category in years at start of year | ||||||||||||
| 50-59 | 448 | 3 | 6.84 | 1.41 to 19.98 | 0.67 | 0.14 to 1.94 | 378 | 8 | 21.82 | 9.42 to 42.99 | 2.12 | 0.92 to 4.13 |
| 60 or above | 2052 | 12 | 5.96 | 3.08 to 10.41 | 0.59 | 0.30 to 1.02 | 2068 | 31 | 15.41 | 10.47 to 21.88 | 1.5 | 1.02 to 2.12 |
| 60–74 | 1435 | 10 | 7.09 | 3.40 to 13.04 | 0.7 | 0.34 to 1.28 | 1383 | 25 | 18.64 | 12.06 to 27.52 | 1.81 | 1.17 to 2.66 |
| 75 or above | 617 | 2 | 3.31 | 0.40 to 11.97 | 0.32 | 0.04 to 1.17 | 685 | 6 | 8.95 | 3.29 to 19.49 | 0.88 | 0.32 to 1.90 |
| Gender | ||||||||||||
| Female | 1503 | 9 | 6.1 | 2.79 to 11.57 | 0.6 | 0.27 to 1.13 | 1474 | 32 | 22.44 | 15.35 to 31.67 | 2.17 | 1.49 to 3.05 |
| Male | 997 | 6 | 6.15 | 2.26 to 13.38 | 0.6 | 0.22 to 1.31 | 972 | 7 | 7.35 | 2.96 to 15.15 | 0.72 | 0.29 to 1.48 |
| RSV subtyping* | ||||||||||||
| RSV A | 2500 | 1 | 0.41 | 0.01 to 2.26 | 0.04 | 0.001 to 0.22 | 2446 | 25 | 10.46 | 6.77 to 15.44 | 1.02 | 0.66 to 1.51 |
| RSV B | 2500 | 12 | 4.89 | 2.53 to 8.54 | 0.48 | 0.25 to 0.84 | 2446 | 9 | 3.74 | 1.71 to 7.11 | 0.37 | 0.17 to 0.70 |
| Severity | ||||||||||||
| Mild | 2500 | 0 | 0 | 0.00 to 1.50 | 0 | 0.00 to 0.15 | 2446 | 0 | 0 | 0.00 to 1.53 | 0 | 0.00 to 0.15 |
| Moderate | 2500 | 1 | 0.41 | 0.01 to 2.26 | 0.04 | 0.001 to 0.22 | 2446 | 3 | 1.25 | 0.26 to 3.64 | 0.12 | 0.03 to 0.36 |
| Severe | 2500 | 14 | 5.71 | 3.12 to 9.58 | 0.56 | 0.31 to 0.94 | 2446 | 36 | 15.12 | 10.59 to 20.94 | 1.47 | 1.03 to 2.03 |
| History of COVID-19 Infection at the start of year | ||||||||||||
| No | 2157 | 12 | 5.67 | 2.93 to 9.90 | 0.56 | 0.29 to 0.97 | 1645 | 23 | 14.36 | 9.10 to 21.54 | 1.4 | 0.89 to 2.09 |
| Yes | 343 | 3 | 8.94 | 1.84 to 26.14 | 0.88 | 0.18 to 2.54 | 801 | 16 | 20.62 | 11.79 to 33.49 | 2 | 1.15 to 3.22 |
Standardised incidence rates were age-gender-adjusted based on 2020 US white population.
Seven (two from year 3, five fromyear 4) RSV tests were from the clinical practice; therefore, RSV subtyping was not completed.
CI for standardised incidence rates was calculated using the normal approximation.
ARI, acute respiratory infection; Attack rate, percentage of subjects with at least one episode (ie, n/N × 100); 95% CI for attack rate, Clopper–Pearson exact 95% CI; 95% CI for incidence rate, exact Poisson 95% CI; Incidence rate per 1000 person-years, number of first episodes per 1000 person-years ; n, number of RSV reported during each year; N, number of subjects at risk during each year; RSV, respiratory syncytial virus.
As the omicron COVID-19 pandemic waned, we observed changes in the incidence and attack rates of RSV-ARI during the 2022–2023 compared with the previous season. We found a total of 39 RSV-ARI cases from 2446 participants (attack rate 1.59% (95% CI 1.14 to 2.17)), all occurring during the RSV season. We found a crude incidence rate of 16.40/1000 PY (95% CI 11.66 to 22.42) and a standardised age-gender adjusted incidence rate of 16.99 cases/1000 PY (95% CI 10.63 to 23.35). When stratified by age, we observed RSV-ARI incidence rate of 21.82 cases/1000 PY (95% CI 9.42 to 42.99) and the attack rate of 2.12% (95% CI 0.92 to 4.13) among adults 50–59 years. In participants 60 years and older, we found RSV-ARI incidence rate of 15.41 cases/1000 PY (95% CI 10.47 to 21.88) and the attack rate during this time was 1.50% (95% CI 1.02 to 2.12) with overlapping CIs between the two age groups. There was a difference between gender, with women having an RSV-ARI incidence rate of 22.44 cases/1000 PY (95% CI 15.35 to 31.67) and the attack rate was 2.17% (95% CI 1.49 to 3.05). While in men a lower incidence rate and attack rates were observed: 7.35 cases/1000 PY (95% CI 2.96 to 15.15) and 0.72% (95% CI 0.29 to 1.48), respectively.
The predominant RSV subtype was RSV B (92%) for 2021 and RSV A (74%) for 2022 (table 2). There were no coinfections in year 3, while we found 4 of the RSV-ARI in year 4 had coinfection with another virus, including COVID-19, rhinovirus, parainfluenza and OC43 coronavirus. We found a seasonal peak of RSV-ARI in December 2021 for year 3 and November 2022 for year 4 (figure 2).
Figure 2. Monthly§ distribution of occurrence of acute respiratory infection (ARI) episodes by respiratory syncytial virus-acute respiratory infection (RSV-ARI) status during year 3 (2021–2022) and year 4 (2022–2023). RSV-ARI = RT-PCR RSV positive ARI episodes, Non-RSV-ARI =RT-PCR RSV negative ARI episodes, Missing RSV-ARI = ARI episodes with missing or invalid RT-PCR RSV results, §A few subjects had ARI episodes with symptoms starting prior to October but were within the 7-day window when swabbed in early October of the given year. *The numbers below the bar graph refers to the number of RSV-ARI episodes.
Healthcare use and outcomes of ARI episodes in years 3 and 4
In 54 RSV-ARI episodes across years 3 and 4, we found no severe outcomes of pneumonia, hospitalisation or death. In 1703, ARI infections were confirmed to be RSV negative, 26 had pneumonia (1.5%) and 14 required hospitalisation (0.8%). The median length of hospital stay was 3 days with no intensive care admissions. The ARI severity was classified as severe in 93% of RSV-ARI and 84% of non-RSV-ARI episodes. Among those without an RSV result (n=574), 7.7% of ARI episodes resulted in emergency department (ED) visits and 2.4% resulted in hospitalisation with one death reported due to COVID-19 (table 3).
Table 3. Summary of complications with ARI episodes and health outcome by RSV-ARI status within 4 weeks since ARI onset date (analysis set for years 3 and 4).
| RSV-ARI episodes (N=54) |
Non-RSV-ARI episodes (N=1703) | Missing RSV-ARI episodes (N=574) |
All ARI episodes (N=2331) |
|
|---|---|---|---|---|
| Complication during ARI | ||||
| None of the complications below, n (%) | 54 (100%) | 1672 (98.2%) | 554 (96.5%) | 2280 (97.8%) |
| Lower respiratory tract disease, n (%) | 0 (0%) | 26 (1.5%) | 11 (1.9%) | 37 (1.6%) |
| Hospitalisation, n (%) | 0 (0%) | 14 (0.8%) | 14 (2.4%) | 28 (1.2%) |
| Death, n (%) | 0 (0%) | 0 (0%) | 1 (0.2%) | 1 (0.0%) |
| Healthcare utilisations | ||||
| Outpatient visits, n (%) | 17 (31.5%) | 332 (19.5%) | 212 (36.9%) | 561 (24.1%) |
| Emergency department visits, n (%) | 0 (0%) | 50 (2.9%) | 44 (7.7%) | 94 (4.0%) |
| Hospitalisation, n (%) | 0 (0.0%) | 14 (0.8%) | 14 (2.4%) | 28 (1.2%) |
| Lengths of stay in hospital, in days | ||||
| Mean (SD) | 3.1 (1.6) | 3.2 (2.8) | 3.1 (2.2) | |
| Median (min, max) | 3 (1, 5) | 2 (0, 11) | 3 (0, 11) | |
| ARI severity, n (%) | ||||
| Mild | 0 (0%) | 36 (2.1%) | 9 (1.6%) | 45 (1.9%) |
| Moderate | 4 (7.4%) | 242 (14.2%) | 63 (11.0%) | 309 (13.3%) |
| Severe | 50 (92.6%) | 1425 (83.7%) | 502 (87.5%) | 1977 (84.8%) |
Note that outcomes are not mutually exclusive.
ARI severity per the protocol:
Mild (no fever or other systemic symptoms or signs of infection but only upper respiratory symptoms).
Moderate (systemic manifestations of infection with upper respiratory symptoms or symptoms requiring a medical appointment (outpatient) for evaluation).
Severe (systemic manifestations of infection with lower respiratory symptoms or symptoms requiring emergency department visit or hospitalisation.
.%, number of episodes in each category; ARI, acute respiratory infection; Missing RSV-ARI, ARI episodes with missing or invalid RT-PCR RSV results; n, number of episodes in each category; N, number of episodes; Non-RSV-ARI, RT-PCR RSV-negative ARI episodes ; RSV, respiratory syncytial virus; RSV-ARI, RT-PCR RSV-positive ARI episodes.
Discussion
In this community-based prospective cohort study of adults aged 50 years and older, we found a 2.7-fold higher incidence and attack rate of RSV in 2022–2023 compared with 2021–2022. In our previously published cohort results in 2019–2020 prior to COVID-19, we found an RSV incidence rate of 48.6 (95% CI 36.9 to 62.9) per 1000 PY and an attack rate of 2.50% (95% CI 1.90 to 3.21) in adults 50 years and older.12 The number of RSV-ARI cases dropped to zero in the 2020–2021 RSV season, which was during the peak of COVID-19 pandemic and prior to widespread use of COVID-19 vaccination.12 However, we observed an increasing trend in the incidence of RSV-ARI among our community following the 2020–2021 season, where circulation of the RSV trended towards its seasonal pattern with a higher infection rate during the winter season. However, this is still lower than the levels reported previously for 2019–2020 RSV season.12 This may reflect the impact of public health measures as we have reported elsewhere9 with estimates of continued 15% mask use in other regions.23 Our current study reports the temporal trends of incidence of RSV-ARI in a community-based cohort of adults ≥50 years (both medically and non-medically attended) following the loosening of the COVID-19 restrictions. Consistent with our findings, a multistate community-based cohort study in adults aged 18–64 years also suggested that RSV-ARI incidence and seasonal patterns are shifting towards pre-COVID-19 pandemic epidemiology.24 In older adults 65 years and older, and in those aged 21 years and older with heart failure or pulmonary conditions, prior to COVID-19 living in the community, an annual attack of 3–7% and 4–10% reported, respectively.5 Additionally, our study uniquely depicts the incidence of RSV-ARI among community dwelling adults in midwest USA before the introduction of RSV vaccines. This study also reflects the unique situation following the COVID-19 pandemic which changed public health practices and potentially population immunity. Most studies are conducted in clinical settings, like hospitals,25 which may not reflect community-level incidence in adults.
Other studies using alternative methodologies to assess the burden of RSV disease reported similar findings during and after the COVID-19 pandemic.
The USA implemented several public health measures, including wearing masks, social distancing and the closure of many businesses and schools in 2020 to reduce the spread of COVID-19.26 We found that 92% of patients in our community were wearing masks and adhering to other public health measures during the COVID-19 pandemic.9 RSV was one of the many respiratory pathogens that reportedly had a drop in its incidence rate with disruption in the viral circulation during this unprecedented time. In Canada, investigators found a dramatic decline of RSV in addition to other respiratory pathogens like influenza A/B and parainfluenza, among others.27 In the USA, a similar dramatic decline was found.8 12 As public health restrictions eased, a rebound of RSV-ARI occurred in the summer of 2021, as noted in children, and adults (≥50 years of age) seeking medical attention for ARI.28 This decline could be from the public health measures or from changes to immunity.29 This finding was also seen in our community-based adult population aged 50 years and older, as we found an increase in RSV-ARI cases following the changes in public health measures.
There are important public health impacts of our findings in the community which have similar patterns in hospitalised patients with RSV. In the RSV Hospitalization Surveillance Network of 8% of the population, the number of hospitalisations from RSV went from a low of 557 hospitalisations in 2020 to 2241 hospitalisations in 2021.30 In our subgroup analysis, in year 4 we observed that participants between 50 and 59 years of age had the highest incidence of RSV-ARI (both medically and non-medically attended) of 21.82 (95% CI 9.42 to 42.99) per 1000 PY compared with 15.41 (95% CI 10.47 to 21.88) per 1000 PY in those aged 60 years and older. This is consistent with our previous findings of the 50–59-year age range with the highest incidence of RSV-ARI.12 These results from the community differ from hospitalised patients with RSV-ARI prior to COVID-19, as higher rates were reported: 33.5–57.5/100 000 in adults aged 50–64 to 136.9–255.6/100 000 in those aged ≥65.31 In contrast, we did not find an incidence rate difference between men and women with RSV-ARI in 2021–2022. Our previous report of RSV-ARI incidence by gender also found similar incidence rates between men and women.12 32 In our community-based cohort, there were small numbers of healthcare utilisation for both RSV-ARI and non-RSV-ARI. There were no RSV-related hospitalisations or deaths among severe RSV-ARI cases (defined as those with LRTD), which may be multifactorial, potentially reflecting the small number of cases as well as underlying community immunity to RSV. We have reported high compliance with public health measures,9 and the population could have continued adherence which prevented transmission of respiratory illnesses.33–37 Most studies evaluating the RSV infection incidence report data for medically attended RSV cases, and thus are not representative of the RSV infection burden in the community, who might not always seek medical care, the gap that we addressed with our current study. In those studies evaluating RSV in the hospital, mortality and mechanical ventilation rates were 12% and were not different compared with COVID-19 or influenza in 2023.38 In patients hospitalised with RSV in a cross-sectional study, 22% of patients developed a cardiac event with a higher percentage in those with heart disease.39 We did find that those participants without swabs had higher healthcare utilisation, where the majority of these participants reflected those with COVID-19 or could have had coinfection and were unable to swab which was a pre-defined procedure in the study.
Our study has several potential clinical and public health applications. Evidence of the effectiveness of public health measures in reducing RSV-ARI and other ARIs may guide recommendations like mask use or staying at home when ill.40 Our findings of higher incidence in adults 50–59 may reflect detection of RSV in a less severe stage in adults with greater exposure to RSV through work or family. This differs from RSV-ARI in the hospital who are typically over 60.38 Our findings highlight that RSV-ARI in adults over 60 years is common in the community and often does not lead to hospitalisation. However, prior studies show that adults hospitalised with RSV-ARI experience more serious adverse health outcomes compared with influenza.41 Given the severity of RSV-ARI in the hospitalised setting, strategies to prevent hospitalisation like vaccination or public health measures seem warranted.
Our study has numerous strengths. First, we had a large prospective cohort of community-based adults aged 50 years and older to determine the RSV incidence, including participants who were both medically and non-medically attended for their ARI, reflecting a more comprehensive view of the infection burden in this community. Second, a decentralised research approach was used, enabling participants to easily perform self-swabbing during their episodes of ARI in the comfort of their own home, increasing compliance to the study protocol,12 and providing a convenient alternative to in-person clinic-based testing.15 Lastly, since the study was extended into the third and fourth years, we were uniquely positioned to capture the longitudinal incidence of RSV-ARI after public health officials eased the COVID-19 pandemic restrictions.
Our study also had some limitations. We conducted our study at a single site in the upper midwest of the USA, and this may not reflect the incidence in other locations. PCR is a superior method of detecting RSV but does not have perfect sensitivity.42 43 Our participants did self-swab, which may not completely replicate technique performed by clinical staff. However, concordance has been reported with 94% sensitivity and 99% specificity in previous RSV studies.44 Some patients did not perform a specimen swab for RSV due to active COVID-19 illness, and thus, the RSV incidence may not capture those participants who might have had coinfection with RSV. Previous rates of coinfection of RSV-ARI and COVID-19 have been reported at 1.6% in adults over 65.45 For healthcare-related outcomes, patients could seek care outside of our healthcare system. The low number of RSV events (15 in 2021–2022, 39 in 2022–2023) limited statistical power for subgroup analyses, resulting in wide CIs. Moreover, the absence of severe outcomes such as hospitalisation and death precluded the characterisation of their associated risk factors. Our cohort mainly consisted of predominately non-Hispanic white adults, which is reflective of the population in the upper midwest of the USA19 and limits the generalisability of these findings to other racial and ethnic groups. The exclusion of individuals with cognitive or mobility impairments, representing a more debilitated and potentially higher-risk group is a limitation of this study, which may limit the generalisability of our findings.
Conclusion
In this large prospective cohort study of community-based adults aged ≥50 years, we found that the incidence of RSV-ARI increased from 2021 to 2022 to 2022–2023 (a 2.7-fold increase in the incidence rate of RSV-ARI), following the lifting of public health measures. This increase in incidence of RSV-ARI may reflect the effectiveness of public health measures during the COVID-19 pandemic and may lead to recommendations during outbreaks of RSV. We acknowledge this was performed at a single centre and used patient self-swab which limits generalisability and fidelity. Given serious adverse health outcomes of RSV-ARI in the hospital, understanding the epidemiology of RSV-ARI in the community is crucial. Future investigations of community RSV-ARI and healthcare-related outcomes in vaccine eligible populations with and without immunisations are warranted to determine the impact of RSV immunisation in different regions within the USA.
Supplementary material
Acknowledgements
We would like to acknowledge Dominique Luyts for her contributions in the study, including in the conception and design of the study.
The funder did not influence the results/outcomes of the study despite author affiliations with the funder.
Footnotes
Funding: This study was sponsored by Mayo Clinic and funded by GSK.
Prepublication history and additional supplemental material for this paper are available online. To view these files, please visit the journal online (https://doi.org/10.1136/bmjopen-2025-111773).
Provenance and peer review: Not commissioned; externally peer reviewed.
Patient consent for publication: Not applicable.
Ethics approval: The study was approved by the Institutional Review Board at the Mayo Clinic (19-004142). Participants gave informed consent to participate in the study before taking part.
Patient and public involvement: Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Data availability statement
All data relevant to the study are included in the article or uploaded as supplementary information.
References
- 1.Joseph NT, Kuller JA, Louis JM, et al. Society for Maternal-Fetal Medicine Statement: Clinical considerations for the prevention of respiratory syncytial virus disease in infants. Am J Obstet Gynecol. 2024;230:B41–9. doi: 10.1016/j.ajog.2023.10.046. [DOI] [PubMed] [Google Scholar]
- 2.Havers FP, Whitaker M, Melgar M, et al. Characteristics and Outcomes Among Adults Aged ≥60 Years Hospitalized with Laboratory-Confirmed Respiratory Syncytial Virus — RSV-NET, 12 States, July 2022–June 2023. MMWR Morb Mortal Wkly Rep. 2022;72:1075–82. doi: 10.15585/mmwr.mm7240a1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Melgar M, Britton A, Roper LE, et al. Use of Respiratory Syncytial Virus Vaccines in Older Adults: Recommendations of the Advisory Committee on Immunization Practices - United States, 2023. MMWR Morb Mortal Wkly Rep. 2023;72:793–801. doi: 10.15585/mmwr.mm7229a4. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Britton A, Roper LE, Kotton CN, et al. Use of Respiratory Syncytial Virus Vaccines in Adults Aged ≥60 Years: Updated Recommendations of the Advisory Committee on Immunization Practices - United States, 2024. MMWR Morb Mortal Wkly Rep. 2024;73:696–702. doi: 10.15585/mmwr.mm7332e1. [DOI] [PubMed] [Google Scholar]
- 5.Falsey AR, Hennessey PA, Formica MA, et al. Respiratory syncytial virus infection in elderly and high-risk adults. N Engl J Med. 2005;352:1749–59. doi: 10.1056/NEJMoa043951. [DOI] [PubMed] [Google Scholar]
- 6.Chuang Y-C, Lin K-P, Wang L-A, et al. The Impact of the COVID-19 Pandemic on Respiratory Syncytial Virus Infection: A Narrative Review. IDR. 2023 doi: 10.2147/IDR.S396434. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Mondal P, Sinharoy A, Gope S. The Influence of COVID-19 on Influenza and Respiratory Syncytial Virus Activities. Infect Dis Rep. 2022;14:134–41. doi: 10.3390/idr14010017. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Rios-Guzman E, Simons LM, Dean TJ, et al. Deviations in RSV epidemiological patterns and population structures in the United States following the COVID-19 pandemic. Nat Commun. 2024;15:3374. doi: 10.1038/s41467-024-47757-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Juhn YJ, Wi C-I, Ryu E, et al. Adherence to Public Health Measures Mitigates the Risk of COVID-19 Infection in Older Adults: A Community-Based Study. Mayo Clin Proc. 2021;96:912–20. doi: 10.1016/j.mayocp.2020.12.016. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Administration USFaD. United States Food and Drug Administration Respiratory syncytial virus. [17-Apr-2025]. https://www.fda.gov/consumers/covid-19-flu-and-rsv/respiratory-syncytial-virus-rsv Available. Accessed.
- 11.Coccia M. Sources, diffusion and prediction in COVID-19 pandemic: lessons learned to face next health emergency. AIMS Public Health. 2023;10:145–68. doi: 10.3934/publichealth.2023012. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Juhn YJ, Wi C-I, Takahashi PY, et al. Incidence of Respiratory Syncytial Virus Infection in Older Adults Before and During the COVID-19 Pandemic. JAMA Netw Open. 2023;6:e2250634. doi: 10.1001/jamanetworkopen.2022.50634. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Pignolo RJ, King KS, Wi C-I, et al. Characteristics of an Older Adult Population Without COVID-19 Infection in a Southeast Minnesota Community. Mayo Clin Proc. 2024;99:1921–32. doi: 10.1016/j.mayocp.2024.05.025. [DOI] [PubMed] [Google Scholar]
- 14.Wi C-I, King KS, Ryu E, et al. Application of Innovative Subject Recruitment System for Batch Enrollment: A Pilot Study. J Prim Care Community Health. 2023;14 doi: 10.1177/21501319231194967. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Wehrhahn MC, Robson J, Brown S, et al. Self-collection: An appropriate alternative during the SARS-CoV-2 pandemic. J Clin Virol. 2020;128:104417. doi: 10.1016/j.jcv.2020.104417. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Health SoMDo Medical records information. https://www.health.state.mn.us/facilities/insurance/clearinghouse/medrecords.html#:~:text=The%20Minnesota%20Health%20Records%20Act%20is%20in%20Minnesota,Section%20144.293%20release%20or%20disclosure%20of%20health%20records n.d. Available.
- 17.von Elm E, Altman DG, Egger M, et al. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement: Guidelines for Reporting Observational Studies. PLoS Med. 2007;4:e296. doi: 10.1371/journal.pmed.0040296. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.World Medical A. World Medical Association Declaration of Helsinki: ethical principles for medical research involving human subjects. JAMA Nov. 2013;310:2191–4. doi: 10.1001/jama.2013.281053. [DOI] [PubMed] [Google Scholar]
- 19.St Sauver JL, Grossardt BR, Leibson CL, et al. Generalizability of epidemiological findings and public health decisions: an illustration from the Rochester Epidemiology Project. Mayo Clin Proc. 2012;87:151–60. doi: 10.1016/j.mayocp.2011.11.009. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Bureau UC Urban and rural. 2024. https://www.census.gov/programs-surveys/geography/guidance/geo-areas/urban-rural.html Available.
- 21.Juhn YJ, Beebe TJ, Finnie DM, et al. Development and initial testing of a new socioeconomic status measure based on housing data. J Urban Health. 2011;88:933–44. doi: 10.1007/s11524-011-9572-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Takahashi PY, Ryu E, Hathcock MA, et al. A novel housing-based socioeconomic measure predicts hospitalisation and multiple chronic conditions in a community population. J Epidemiol Community Health. 2016;70:286–91. doi: 10.1136/jech-2015-205925. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Evaluation IfHMa Mask usage. 2025. https://covid19.healthdata.org/united-states-of-america?view=mask-use&tab=trend Available.
- 24.Bosch W, Speiser LJ, Wi C-I, et al. Incidence of Respiratory Syncytial Virus in Community-Dwelling Adults Aged 18-64 Years Over 2 Seasons, 2022-2024, in a North American Community. Open Forum Infect Dis. 2024;11:ofae597. doi: 10.1093/ofid/ofae597. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25.Hanage WP, Schaffner W. Burden of Acute Respiratory Infections Caused by Influenza Virus, Respiratory Syncytial Virus, and SARS-CoV-2 with Consideration of Older Adults: A Narrative Review. Infect Dis Ther. 2025;14:5–37. doi: 10.1007/s40121-024-01080-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 26.Lopes GS, Manemann SM, Weston SA, et al. Minnesota COVID-19 Lockdowns: The Effect on Acute Myocardial Infarctions and Revascularizations in the Community. Mayo Clin Proc Innov Qual Outcomes. 2022;6:77–85. doi: 10.1016/j.mayocpiqo.2021.12.002. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Groves HE, Piché-Renaud P-P, Peci A, et al. The impact of the COVID-19 pandemic on influenza, respiratory syncytial virus, and other seasonal respiratory virus circulation in Canada: A population-based study. The Lancet Reg Health Am. 2021;1:100015. doi: 10.1016/j.lana.2021.100015. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Falsey AR, Cameron A, Branche AR, et al. Perturbations in Respiratory Syncytial Virus Activity During the SARS-CoV-2 Pandemic. J Infect Dis. 2022;227:83–6. doi: 10.1093/infdis/jiac434. [DOI] [PubMed] [Google Scholar]
- 29.Abu-Raya B, Viñeta Paramo M, Reicherz F, et al. Why has the epidemiology of RSV changed during the COVID-19 pandemic? EClinicalMedicine. 2023;61:102089. doi: 10.1016/j.eclinm.2023.102089. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 30.Havers FP, Whitaker M, Melgar M, et al. Burden of Respiratory Syncytial Virus-Associated Hospitalizations in US Adults, October 2016 to September 2023. JAMA Netw Open. 2024;7:e2444756. doi: 10.1001/jamanetworkopen.2024.44756. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 31.Branche AR, Saiman L, Walsh EE, et al. Change in functional status associated with respiratory syncytial virus infection in hospitalized older adults. Influenza Other Respir Viruses. 2022;16:1151–60. doi: 10.1111/irv.13043. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 32.Groeneveld JM, Ballering AV, van Boven K, et al. Sex differences in incidence of respiratory symptoms and management by general practitioners. Fam Pract. 2020;37:631–6. doi: 10.1093/fampra/cmaa040. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 33.Matias G, Taylor R, Haguinet F, et al. Estimates of hospitalization attributable to influenza and RSV in the US during 1997-2009, by age and risk status. BMC Public Health. 2017;17:271. doi: 10.1186/s12889-017-4177-z. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 34.Malosh RE, Martin ET, Callear AP, et al. Respiratory syncytial virus hospitalization in middle-aged and older adults. J Clin Virol. 2017;96:37–43. doi: 10.1016/j.jcv.2017.09.001. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 35.Falsey AR, Walsh EE, House S, et al. Risk Factors and Medical Resource Utilization of Respiratory Syncytial Virus, Human Metapneumovirus, and Influenza-Related Hospitalizations in Adults-A Global Study During the 2017-2019 Epidemic Seasons (Hospitalized Acute Respiratory Tract Infection [HARTI] Study) Open Forum Infect Dis. 2021;8:ofab491. doi: 10.1093/ofid/ofab491. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 36.Maggi S, Veronese N, Burgio M, et al. Rate of Hospitalizations and Mortality of Respiratory Syncytial Virus Infection Compared to Influenza in Older People: A Systematic Review and Meta-Analysis. Vaccines (Basel) 2022;10:2092. doi: 10.3390/vaccines10122092. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 37.Heppe-Montero M, Gil-Prieto R, del Diego Salas J, et al. Impact of Respiratory Syncytial Virus and Influenza Virus Infection in the Adult Population in Spain between 2012 and 2020. IJERPH. 2012;19:14680. doi: 10.3390/ijerph192214680. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 38.Surie D, Yuengling KA, DeCuir J, et al. Severity of Respiratory Syncytial Virus vs COVID-19 and Influenza Among Hospitalized US Adults. JAMA Netw Open. 2024;7:e244954. doi: 10.1001/jamanetworkopen.2024.4954. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 39.Woodruff RC, Melgar M, Pham H, et al. Acute Cardiac Events in Hospitalized Older Adults With Respiratory Syncytial Virus Infection. JAMA Intern Med. 2024;184:602–11. doi: 10.1001/jamainternmed.2024.0212. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 40.Mosscrop LG, Williams TC, Tregoning JS. Respiratory syncytial virus after the SARS-CoV-2 pandemic - what next? Nat Rev Immunol. 2022;22:589–90. doi: 10.1038/s41577-022-00764-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 41.Surie D, Yuengling KA, DeCuir J, et al. Disease Severity of Respiratory Syncytial Virus Compared with COVID-19 and Influenza Among Hospitalized Adults Aged ≥60 Years — IVY Network, 20 U.S. States, February 2022–May 2023. MMWR Morb Mortal Wkly Rep. 2022;72:1083–8. doi: 10.15585/mmwr.mm7240a2. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 42.Hu A, Colella M, Tam JS, et al. Simultaneous detection, subgrouping, and quantitation of respiratory syncytial virus A and B by real-time PCR. J Clin Microbiol. 2003;41:149–54. doi: 10.1128/JCM.41.1.149-154.2003. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 43.Ramirez J, Carrico R, Wilde A, et al. Diagnosis of Respiratory Syncytial Virus in Adults Substantially Increases When Adding Sputum, Saliva, and Serology Testing to Nasopharyngeal Swab RT-PCR. Infect Dis Ther. 2023;12:1593–603. doi: 10.1007/s40121-023-00805-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 44.Suntarattiwong P, Mott JA, Mohanty S, et al. Feasibility and Performance of Self-Collected Nasal Swabs for Detection of Influenza Virus, Respiratory Syncytial Virus, and Human Metapneumovirus. J Infect Dis. 2021;224:831–8. doi: 10.1093/infdis/jiab023. [DOI] [PubMed] [Google Scholar]
- 45.Trifonova I, Korsun N, Madzharova I, et al. Epidemiological and Genetic Characteristics of Respiratory Viral Coinfections with Different Variants of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Viruses. 2024;16:958. doi: 10.3390/v16060958. [DOI] [PMC free article] [PubMed] [Google Scholar]