Two new studies, one based on households in southeast Michigan and one involving hospitalized Japanese adults, compare respiratory syncytial virus (RSV) to seasonal flu and describe co-infection dynamics between the common and transmissible respiratory viruses and how they differ in disease severity.
Coinfection common
In the first study, published in Nature Communications, researchers enrolled 4,029 participants from 957 households in a prospective household cohort study to establish how viral coinfection and cocirculation may affect transmission of both symptomatic influenza and RSV infections.
The Household Influenza Vaccine Evaluation (HIVE) study was conducted from 2010 to 2020. Altogether, 546 household clusters involved influenza A virus (IAV), with 786 total cases, 231 clusters involved influenza B virus (IBV), with 301 total cases, and 370 clusters involved RSV, with 493 total cases. There were 201 coinfections involving influenza A virus, 67 involving influenza B virus, and 181 involving RSV.
Of all secondary cases, 27.0% involved influenza A, 19.6%, influenza B, and 21.9% RSV.
The authors said the proportion of coinfected cases was significantly different across viruses.
“For RSV, 39.0% of index cases and 28.7% of secondary cases were coinfected, compared to IAV (27.5% of index, 20.3% of secondary) and IBV (23.1% of index, 18.6% of secondary,” the authors wrote. “The two most identified coinfecting and cocirculating viruses were rhinovirus/enterovirus (RV/EV) and human coronaviruses (HCoV).”
Young index patient ups the risk of transmission
For all patients infected with IAV, IBV, or RSV, more than 60% of index cases and secondary cases had received the seasonal flu vaccine.
Having a school-age child (under the age of 18) as an index case-patient was associated with a greater risk of transmission for IAV (incidence rate ratio, 2.13; 95% confidence interval [CI], 1.46 to 3.10), but not for IBV or RSV.
If an index patient was coinfected, there was a reduced transmission of IAV and RSV, the authors said.
“Our findings suggest that respiratory virus transmission may be impacted by other viruses coinfecting individuals and cocirculating within households,” the authors concluded.
More severe RSV outcomes in adults
In the Japanese study, published in Infectious Diseases, authors looked at outcomes among hospitalized adult RSV patients. To do so, they compared health outcomes among 56,980 adult patients hospitalized for RSV or influenza infection from April 2010 to March 2022.
“While RSV is a well-recognized pathogen in children under 5 years of age, its burden in adults, especially older adults, has been increasingly recognized in recent years,” the authors wrote.
While in-hospital mortality was not significantly different between the two patient groups (7.5% for RSV and 6.6% for flu), RSV patients showed more severe outcomes, especially for patients 60 years and older.
RSV patients prescribed more drugs
While hospitalized, RSV patients were prescribed significantly more antibiotics and antifungals—which are ineffective against viruses—as well as both inhaled and systemic steroids. The RSV group also had an increased risk of mechanical ventilation use than the influenza group, 9.7% compared to 7.0%, (risk ratio [RR], 1.35; 95% confidence interval [CI], 1.08 to 1.67).
The RSV group had a significantly increased risk of readmission due to any cause within 1 year after surviving discharge than did the flu group 34.0% versus 28.9%, (RR, 1.19; 95% CI, 1.07 to 1.32).
Our study found that the threat of RSV infection in adults was at least comparable to or greater than the health threat of influenza.
Finally, median hospital stay was longer in the RSV group than in flu patients (12 days vs. 10 days).
“Our study found that the threat of RSV infection in adults was at least comparable to or greater than the health threat of influenza,” the authors concluded. “Especially in older people, RSV infection was found to be a significant health threat.”
