Risk factors for respiratory syncytial virus associated with acute lower respiratory infection in children under five years: Systematic review and meta-analysis

Background Respiratory syncytial virus (RSV) is the most common pathogen identified in young children with acute lower respiratory infection (ALRI) as well as an important cause of hospital admission. The high incidence of RSV infection and its potential severe outcome make it important to identify and prioritise children who are at higher risk of developing RSV-associated ALRI. We aimed to identify risk factors for RSV-associated ALRI in young children. Methods We carried out a systematic literature review across 4 databases and obtained unpublished studies from RSV Global Epidemiology Network (RSV GEN) collaborators. Quality of all eligible studies was assessed according to modified GRADE criteria. We conducted meta-analyses to estimate odds ratios with 95% confidence intervals (CI) for individual risk factors. Results We identified 20 studies (3 were unpublished data) with "good quality" that investigated 18 risk factors for RSV-associated ALRI in children younger than five years old. Among them, 8 risk factors were significantly associated with RSV-associated ALRI. The meta-estimates of their odds ratio (ORs) with corresponding 95% confidence intervals (CI) are prematurity 1.96 (95% CI 1.44- 2.67), low birth weight 1.91 (95% CI 1.45-2.53), being male 1.23 (95% CI 1.13-1.33), having siblings 1.60 (95% CI 1.32-1.95), maternal smoking 1.36 (95% CI 1.24-1.50), history of atopy 1.47 (95% CI 1.16-1.87), no breastfeeding 2.24 (95% CI 1.56-3.20) and crowding 1.94 (95% CI 1.29-2.93). Although there were insufficient studies available to generate a meta-estimate for HIV, all articles (irrespective of quality scores) reported significant associations between HIV and RSV-associated ALRI. Conclusions This study presents a comprehensive report of the strength of association between various socio-demographic risk factors and RSV-associated ALRI in young children. Some of these amenable risk factors are similar to those that have been identified for (all cause) ALRI and thus, in addition to the future impact of novel RSV vaccines, national action against ALRI risk factors as part of national control programmes can be expected to reduce burden of disease from RSV. Further research which identifies, accesses and analyses additional unpublished RSV data sets could further improve the precision of these estimates.