Burden of RSV infections among young children in primary care: a prospective cohort study in five European countries (2021-23)

Background: The majority of respiratory syncytial virus (RSV) infections in young children are managed in primary care, however, the disease burden in this setting remains poorly defined.

Methods: We did a prospective cohort study in primary care settings in Belgium, Italy, Spain, the Netherlands, and the UK during the RSV seasons of 2020-21 (UK only; from Jan 1, 2021), 2021-22, and 2022-23. Children aged younger than 5 years presenting to their general practitioner or primary care paediatrician with symptoms of an acute respiratory tract infection were eligible for RSV testing. Children who tested positive for RSV were consented and followed up for 30 days via a physician clinical report (initial primary care visit on day 1) and two parent-report questionnaires (days 14 and 30). We assessed the burden of RSV in terms of clinical course (symptoms, illness duration, and complications), health-care resource utilisation (primary care visits, emergency department visits, hospitalisation rate, and medication use), and societal impact (daycare or school absence and parental work absence) for the 30-day follow-up period.

Findings: Among 3414 tested children, 1124 (32·9%; 95% CI 31·3-34·5) tested positive for RSV. Among children with data on age, RSV positivity rate was 38·9% (36·1-41·7; n=466 of 1198) in children younger than 1 year and 25·9% (24·0-27·9; n=513 of 1979) in those aged 1 to <5 years. Of the 1124 RSV-positive children, 878 (78·1%) were enrolled and had day 1 data collected (median age 11·1 months [IQR 6·0-22·0]; 446 [50·9%] boys and 431 [49·1%] girls [N=877]). RSV illness lasted a mean of 11·7 days (95% CI 11·2-12·2; n=794). At day 14 and day 30, any remaining symptoms were reported in 451 of 804 (56·1% [95% CI 52·6-59·6]) and 261 of 724 (36·0% [32·6-39·7]) children. The mean number of primary care visits per child ranged from 1·4 (95% CI 1·2-1·6; the Netherlands) to 3·0 (2·8-3·3; Spain), and was higher in children younger than 1 year (2·7 visits [2·4-2·9]) than in those aged 1 to <5 years (2·1 [1·9-2·2]). Prescribed medication use varied, from 25 of 96 children (26·0% [95% CI 17·6-36·0]; the UK) to 228 of 297 children (76·8% [71·5-81·5]; Italy), with bronchodilators and antibiotics being the most commonly prescribed medicines across all countries. Prescribed medication use was reported in 258 of 418 children aged 1 to <5 years (61·7% [56·9-66·4]) and 196 of 394 children younger than 1 year (49·7% [44·7-54·8]). Missed working days by parents due to their child's RSV illness were reported in 340 of 744 cases (45·7% [42·1-49·4]); the mean number of missed workdays ranged from 1·3 days (95% CI 0·5-2·2) in Spain to 4·1 days (3·3-5·0) in Belgium.

Interpretation: RSV infections in children younger than 5 years in primary care are associated with substantial symptomatology, health-care utilisation, and parental work absence. Notable differences in RSV burden existed across countries, likely due to differences in primary health-care systems, clinical practice, and health-care-seeking behaviour. This study emphasises the importance of considering country-specific primary care burden estimates when considering the implementation of RSV immunisations programmes.

Funding: Sanofi and AstraZeneca.