Photo Credit: JUN LI

A literature review of RSV incidence suggests the need for global, multi-age data to guide future studies on RSV incidence and vaccination strategies.

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A review published in The Journal of Infectious Diseases highlights gaps in existing knowledge about RSV. Benjamin Doty and colleagues searched for articles that reported RSV incidence rates and cumulative incidences worldwide. The initial search returned 528 articles; 37 studies were included in the review. Case series, cross-sectional studies, and studies that only estimated the frequency of RSV infection were excluded.

“Primary studies of RSV occurrence in adults typically report estimates by country, area, or age group,” researchers wrote. “Reviews that include data from multiple countries, areas, and age groups are needed to guide future observational studies on RSV incidence and vaccination strategies by, for example, identifying regions and subpopulations at most need for a vaccine.” 

Twenty-four studies conducted on six continents examined the incidence of RSV in medically attended patients. Among adults, Doty and colleagues wrote, these studies showed that the incidence of RSV-related hospitalizations ranged from zero to 1,040 per 100,000 person-years, whereas the incidence of RSV-related outpatient visits ranged from 20 to 2,320 cases per 100,000 person-years. For patients aged 50 to 64, hospitalization incidences ranged from zero to 170 cases per 100,000 person-years, whereas for those aged 65 and older, incidences ranged from 5 to 130.

Comorbid Conditions

RSV is of particular concern among patients living with cardiac or pulmonary diseases. A study from Thailand reported that in adults aged 65 and older with at least one medical condition, the RSV incidence rate was 2,320 per 100,000 person-years (95% CI, 1,250–3,950) from 2015 to 2017. A British study reported a range of zero hospitalizations for adults aged 18 to 49 to 75 per 100,000 person-years among those aged 75 and up. Four American studies found that the incidence rate of hospitalizations among patients with chronic heart failure or COPD was as much as 18,000 per 100,000 person-years.

Patients with end-stage renal disease who were 50 to 64 years old had a seasonal incidence of 87.7 (95% CI, 6.7-168.6) per 100,000 person-years, and patients of the same age with diabetes had an incidence of 16.2 (95% CI, 9.6-22.8), one New Zealand study found. In those aged 65 to 80, the incidence rates were 39.7 per 100,000 person-years (95% CI, 15.2-94.6) for renal disease and 52.8 (95% CI, 36.1-69.4) for diabetes.

Patients with hematologic malignancies had significant incidence rates of RSV. Across four studies with a follow-up between 30 days and 2 years, people with blood cancer showed a cumulative incidence ranging from 2.4% to 21.6%.

Remaining Gaps in Epidemiology

Overall, Doty and colleagues found that RSV incidence increased with age in all populations, with the highest rates seen in older adults with underlying conditions. The most evidence of RSV incidence was from high-income regions. They also noted that case definitions of RSV disease varied from one study to another.

“The reported RSV incidence data should be considered in light of the potential impact of tests used to detect the virus and surveillance tools used to identify infected patients,” the researchers noted. “PCR testing of nasopharyngeal swabs is the most sensitive and commonly used method in hospitals and was the diagnostic method in 22 studies captured in this analysis. However, this method is known to be less sensitive for upper than lower respiratory tract infections, largely due to inadequate viral load on nasopharyngeal specimens (particularly in adults), resulting in missed cases and underdiagnosis. Adding multiple specimen types (eg, saliva, sputum, serum) increased the RSV detection rate, while testing of all four specimen types doubled the diagnostic yield.”

The researchers noted that better methods for identifying RSV may provide more precise incidence rates and determine “the true extent” of RSV’s burden. 

“Several gaps in the literature were identified, including the need for more evidence on RSV incidence in community-based populations and LMI regions,” Doty and colleagues concluded. “Furthermore, consistency across studies in the common surveillance case definition used for RSV testing, the case definition of RSV-associated ARI, and the measurement and presentation of RSV incidence would facilitate comparing the incidence estimates across time and geographies. Such evidence is critical to understanding the potential impact of RSV vaccines in adult populations globally.”

Key Takeaways

• Most studies examined the incidence of RSV in medically attended patients.
• Researchers examined RSV severity in patients with pulmonary and cardiovascular conditions, diabetes, and cancer.
• Case definitions of RSV and testing methodologies varied from study to study.
• There is a need for more evidence of RSV incidence in the community.