Estimating the burden of RSV- and influenza-associated hospitalizations, ICU admissions, and deaths across age and socioeconomic groups in New York State, 2005-2019

Abstract

Background: Multiple prophylactic products are now available to protect against respiratory syncytial virus (RSV) in different age groups. Assessing the pre-intervention burden of RSV infections across various severity levels and risk groups is crucial, as it provides a baseline for evaluating the impact of these products.

Methods: We obtained monthly time series data on hospitalizations, intensive care unit (ICU) admissions, and deaths by age group, ZIP code, and cause for New York state from 2005 to 2019. Socioeconomic status (SES) of the ZIP codes was classified using supervised principal component analysis (PCA). We estimated the incidence of hospitalizations, ICU admissions, and deaths attributable to RSV and to influenza using hierarchical Bayesian regression models. Additionally, we assessed severity, defined by ICU admission and mortality risks, as well as recording fraction (i.e., percent of estimated virus-associated hospitalizations recorded as being due to the specific virus), stratified by age, SES, and over time.

Results: The estimated annual incidence of RSV-associated hospitalizations and ICU admissions were highest in infants under 1 in the low SES group (2,240 [95% credible interval (CrI): 2,200-2,290] hospitalizations and 330 [95% CrI: 320-350] ICU admissions per 100,000 person-years). The incidence of RSV-associated deaths was highest among adults ≥85 years old (61 [95% CrI: 49-74] per 100,000 person-years). In contrast to RSV, the burden of influenza was greatest in age groups ≥65 years. The risk of ICU admission varied by patients' age and SES, and the mortality risk increased dramatically with age for both pathogens (RSV: 11.9% [95% CrI: 9.6-14.3%], influenza: 14.4% [95% CrI: 13.1-15.6%] among ≥85 year age group). Incidence varied by epidemic year and season, and we observed an increasing recording fraction of RSV among all age groups over the study period.

Conclusions: RSV and influenza contribute significantly to the burden of hospitalizations, ICU admissions, and deaths, particularly among infants and older adults. Although the recording fraction of RSV increased over the study period, it remains lower, particularly for adults. Our findings reveal a disparity in hospitalization burden by SES, particularly among younger age groups.

Figure 1.. Estimated incidence of RSV- and influenza-associated hospitalizations (A), ICU admissions (B), and deaths (C), 2005–2019.

The dots indicate the posterior median estimates of the incidence of hospitalizations, ICU admissions, and deaths that are attributable to RSV or influenza per 100,000 person-years, with the labels indicating the estimated values. The error bars indicate the 95% credible intervals of the estimated incidence.

Figure 2.. Estimated incidence of RSV- and influenza-associated hospitalizations, ICU admissions, and deaths over time by age group, 2005–2019.

The pale grey blocks represent the time period of transition of the ICD coding system from ICD-9-CM to ICD-10-CM in 2015. The dots represent the posterior median estimates of the incidence rate of hospitalizations, ICU admissions, and deaths that are attributable to RSV or influenza per 100,000 person-years for each season. The error bars indicate the 95% credible intervals of the estimated incidence. The four vertical panels indicate the incidence estimates for age groups <1, 1-<2, 65–84, and ≥85 years old.

Figure 3.. Monthly incidence of recorded RSV-coded, estimated RSV-associated, and estimated all-cause respiratory outcomes among infants under 1 year old, July 2005 - June 2019.

The red area represents the incidence of outcomes recorded as being due to RSV in the HCUP database (RSV-coded outcomes). The yellow area represents the posterior median incidence of RSV-associated outcomes estimated from the model. The blue area represents the posterior median incidence of all-cause respiratory outcomes estimated from the model.

Figure 4.. Monthly incidence of recorded RSV-coded, estimated RSV-associated, and estimated all-cause respiratory outcomes among adults aged 65 and above, July 2005 - June 2019 (left: original; right panel: zoomed in).

The red area represents the incidence of outcomes recorded as being due to RSV in the HCUP database (RSV-coded outcomes). The yellow area represents the posterior median incidence of RSV-associated outcomes estimated from the model. The blue area represents the posterior median incidence of all-cause respiratory outcomes estimated from the model.

Figure 5.. Percent of respiratory outcomes attributable to RSV and influenza infection, July 2005 - June 2019.

The bars show the posterior median percent of all-cause respiratory outcomes (hospitalizations, ICU admissions, and deaths) that were estimated to be attributable to RSV or influenza infection, calculated as the estimated incidence of RSV-/influenza-associated outcomes divided by the estimated incidence of all-cause respiratory outcomes. The texts above the bars label the detailed numbers of the medians. The error bars indicate the 95% credible intervals of the estimated attributable percent.

Figure 6.. Estimated proportion of RSV- and influenza-associated hospitalizations admitted to the ICU admission (A) and resulting in death (B), July 2005 - June 2019.

The dots indicate posterior median estimates of the proportion of RSV- and influenza-associated hospitalizations admitted to the ICU or dying. The error bars indicate the 95% credible intervals of the estimated ICU admission and mortality risk. ICU admission risk is defined as the ratio between the incidence of virus-associated ICU admission and the incidence of virus-associated hospitalizations; the mortality risk is defined as the ratio between the incidence of virus-associated deaths and the incidence of virus-associated hospitalizations.

Figure 7.. Percent of RSV-associated hospitalizations recorded as being due to RSV and influenza.

Panel A) and C): Recording fraction of (A) RSV- and (C) influenza-associated hospitalizations, 2005–2019. The recording fraction is defined as the ratio of the number of RSV-coded and estimated RSV-associated hospitalizations. The bars represent the posterior median estimates of the recording fractions, and the error bars represent the 95% credible intervals of the estimates. Panel B) and D): Recording fraction of (B) RSV- and (D) influenza-associated hospitalizations over time by age. The dots represent the median estimates of the recording fraction, and the error bars represent 95% credible intervals of the estimates.