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

Abstract

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.

Keywords: Influenza a/b; Influenza-like illness; Respiratory syncytial virus; SARS-CoV-2; Surveillance; Symptoms; Vaccination.

Fig. 1

Percentage (95% CI) reporting ILI-WHO (full CIS and respiratory pilot) and test positivity for SARS-CoV-2 (full CIS and respiratory pilot), influenza A/B (respiratory pilot) and RSV (respiratory pilot). Note: SY, school year. See Additional file 1 for raw daily percentages for the full CIS sample (Additional file 1: Fig. S15) and cumulative numbers positive for SARS-CoV-2, influenza A/B and RSV, and reporting ILI-WHO in the respiratory pilot (Additional file 1: Fig. S16)

Fig. 2

Estimated incidence (95%CI) of SARS-CoV-2 (full CIS), RSV (respiratory pilot), and influenza A/B (respiratory pilot). Note: Time frame covering October 24, 2022–February 13, 2023. SY, school year. Estimates based on a Weibull-ILI survival curve for infection duration. See Additional file 1 for further details on survival distributions (Additional file 1: Table S1, Figure S5)

Fig. 3

Prevalence of reported symptoms by SARS-CoV-2 test result (full CIS sample), and amongst those testing positive for RSV and influenza A/B (respiratory pilot). Note: See Additional file 1: Fig. S6–S7 for the remaining symptoms. Predictions are averaged across time (no smooth for calendar time included in models). The respiratory pilot analysis excluded loss of smell due to the small absolute number of participants reporting this symptom. Predictions were restricted to ages 10–75 years for the respiratory pilot due to the small absolute number outside this range (approximate 5^th–95^th percentiles), and 5–85 years for the full CIS (approximate 1^st–99^th percentiles)

Fig. 4

For participants reporting selected symptoms, predicted probabilities of a positive test result for SARS-CoV-2 on 15 December 2022 (full CIS sample), and for SARS-CoV-2, influenza A/B or RSV (respiratory pilot sample), by age. Note: See Additional file 1: Fig. S8–S9, for the remaining symptoms. Predictions for the full CIS sample were made on 15 December 2022 from models which adjusted for time, results for additional dates are shown in Additional file 1: Fig. S17. Predictions for the respiratory pilot are from a model not adjusted for time (given the limited sample size) and therefore represent an overall average over time. Predictions were made for ages 5–85 (approx. 1^st–99^th percentiles)