RSV vs HMPV in Children: Clinical Features in Hospital Settings

Source: Goldstein LA, Michaels MG, Salthouse A, et al. Human metapneumovirus and respiratory syncytial virus in children: a comparative analysis. Pediatrics. 2025;156(3):e2024070218; doi: 10.1542/peds.2024-070218.Investigators from multiple institutions conducted a prospective study to compare demographic and clinical characteristics of children seen in the emergency department (ED) or with an inpatient (IP) admission who had respiratory syncytial virus (RSV) or human metapneumovirus (HMPV) acute respiratory infection (ARI). Patients seen in the ED or during an IP admission with ARI caused by RSV or HMPV, confirmed by PCR, were enrolled at 7 pediatric centers in the US from December 2016 to March 2020. Demographics and clinical characteristics were compared in patients with RSV or HMPV with chi-square, Fisher exact, or Wilcoxon rank-sum tests. Seasonality was assessed by determining the peak percent positivity for RSV and HMPV during 3-week rolling averages. Disease severity was evaluated using 3 outcomes: hospital admission (for children seen in the ED), and ICU admission and length of stay (LOS) >3 days (for patients hospitalized). Logistic regression was used to compare the likelihood of each of these outcomes in study participants in the RSV or HMPV group, after controlling for confounding variables.Data were analyzed on 8,605 children, including 5,329 with an IP admission (4,398 with RSV and 931 with HMPV) and 3,276 enrolled in the ED (2,371 with RSV and 905 with HMPV). The median age of patients with RSV was significantly younger than that of HMPV, both in the ED (15 vs 22 months; P <0.0001) and with IP admissions (7 vs 16 months; P <0.0001). Among children with IP admission, 45.3% of those with HMPV had at least 1 underlying condition, compared to 23.5% of those with RSV (P <0.0001). There were no significant differences between patients hospitalized with RSV or HMPV for percent requiring supplemental oxygen or LOS. However, those with HMPV were significantly more likely to require mechanical ventilation (5.9% vs 3.9% for children with RSV; P = 0.006). RSV detections peaked between November and January, and HMPV peaked in March. Patients seen in the ED with RSV were more likely to require hospitalization than those with HMPV (adjusted odds ratio [aOR], 1.68; 95% confidence interval [CI], 1.50, 1.87), particularly among the subgroup of children <6 months old (aOR, 3.27; 95% CI, 2.53, 4.23). There was no significant difference between hospitalized patients with RSV or HMPV in need for ICU admission (aOR, 1.10; 95% CI, 0.92, 1.33) or LOS >3 days (aOR, 0.99; 95% CI, 0.85, 1.15).The authors conclude that children hospitalized with HMPV were older and more likely to have an underlying condition than patients with RSV.Dr Loyal disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.In the current study, investigators report on a comparative analysis of 2 common respiratory viruses associated with hospitalization in children. The study’s strengths include a prospective approach, inclusion of patients from multiple sites, and a large sample size. Investigators chose to focus on the study period before the COVID-19 pandemic in 2020, when the patterns of RSV and HMPV circulation were more predictable.Investigators in the current study found that children hospitalized with RSV tended to be younger, and those under 6 months were more likely to be hospitalized than those with HMPV. This finding underscores the importance of RSV immunoprophylaxis, now more broadly available for term infants up to 8 months of age.1 According to the CDC, in clinical studies among infants who were born during or entering their first RSV season, pooled efficacy from Phase II and III clinical trials in preventing RSV-associated lower respiratory tract infection hospitalization, evaluated through 150 days, was 80.6%.1 Of infants eligible for nirsevimab in the 2023-24 season in the US, uptake was estimated to be 51.2%.1 With growing public skepticism amidst mixed messages about public health prevention efforts in infancy, the medical and public health communities have much work to do to continue to educate families.If efforts to prevent RSV among young infants are successful, the authors point out the potential for HMPV to emerge as the next major threat as the epidemiology of the circulation of viruses continues to evolve. The more frequent association of comorbidities observed with HMPV than RSV may suggest that comorbidities weaken the immune response to HMPV. Previous studies have found frequent co-infections with other viruses, including RSV.3As the proportion of hospitalizations among children with medical complexity increases in the US,4 we should be prepared to potentially see more HMPV. Importantly there are no approved preventive or therapeutic interventions for HMPV at this time.3Both RSV and HMPV are formidable threats, more so for younger infants with RSV and older infants with comorbidities infected with HMPV. (See AAP Grand Rounds. 2024;52[5]:51.)5