# Age-related disparities in clinical characteristics and outcomes of patients with severe fever with thrombocytopenia syndrome

## TL;DR

Older patients with SFTS have worse clinical outcomes and immune responses compared to younger patients, suggesting the need for age-specific treatment strategies.

## Contribution

This study identifies age ≥65 as an independent risk factor for poor prognosis in SFTS patients.

## Key findings

- Patients aged ≥65 years had higher levels of liver, kidney, heart, and coagulation injury markers and higher viral loads.
- Older patients had lower CD3+ and CD3+CD4+ lymphocyte counts and higher pro-inflammatory markers.
- Age ≥65 years was an independent predictor of in-hospital mortality in SFTS patients.

## Abstract

The exploration of age-related clinical characteristics and prognosis of severe fever with thrombocytopenia syndrome (SFTS) has not been extensively addressed in current research. This study aimed to analyze the differences in clinical features and outcomes of SFTS patients across various age groups.

Patients were assigned to four groups: those aged ≤ 54 years, those aged 55–64 years, those aged 65–74 years, and those aged ≥ 75 years. Then, their clinical data were compared.

A total of 253 patients diagnosed with SFTS were retrospectively included. Compared with patients aged < 65 years, patients aged ≥ 65 years had higher serum levels of laboratory parameters indicating liver, kidney, heart, and coagulation system injury, as well as a higher viral load. Moreover, the serum levels of procalcitonin, SAA, ferritin, IL-6, IL-10, and TNF-α were significantly higher, but the percentages and counts of CD3+ and CD3 + CD4 + lymphocytes were significantly lower in patients aged ≥ 65 years than in patients aged < 65 years. The cumulative survival rate of patients aged ≥ 65 years was also significantly lower than that of patients aged < 65 years. Univariate and multivariate logistic regression analyses identified that age ≥ 65 years was an independent risk factor for the prognosis of patients with SFTS.

Age significantly influences the clinical features and prognosis of patients, and age ≥ 65 years is associated with adverse outcomes in patients with SFTS.

We reported the differences in the clinical characteristics, including demographics, comorbidities, clinical symptoms, laboratory test results, complications, and treatment in severe fever with thrombocytopenia syndrome (SFTS) patients across four age groups. It was demonstrated that patients aged ≥65 years had a significantly lower cumulative survival rate compared to those aged <65 years, and age ≥ 65 years was an independent predictor of in-hospital mortality of patients with SFTS. Our study provided evidence of the impact of age on clinical characteristics and outcomes of SFTS, which suggested that tailored treatment strategies may be necessary among different age groups.