Fever with thrombocytopenia syndrome (SFTS) is an infectious disease that occurs frequently in the spring and summer months and is caused by a novel Bunyavirus (SFTSV). The patient's main presentations include fever, decreased white blood cell and platelet counts, decreased lymphocyte counts, enlarged lymph nodes, malaise, and gastrointestinal symptoms. In most cases, the prognosis is favorable. However, the condition of critically ill patients deteriorates rapidly and may lead to shock, respiratory failure, disseminated intravascular coagulation (DIC), multi-organ failure, and death [1–4]. Early assessment of disease prognosis and timely emergency measures are crucial.
Yu Dong et al [7] studied the epidemiologic distribution, clinical characteristics, and prognostic risk factors of SFTS patients and concluded that the risk factors for poor prognosis in patients with severe SFTS were advanced age, history of multiple underlying medical conditions, high viral load, severely reduced platelet count, and delayed treatment; Gai ZT et al [8] found that 7–13 days after the onset of the disease is an important period in determining disease regression and that high viral load is one of the risk factors for case fatality. High viral load is one of the risk factors for case fatality. The possible mechanism of these two factors, advanced age, and high viral load is that, on the one hand, as people age, the immune system of the elderly gradually ages, leading to an increase in systemic inflammation. After the decline of immune function, when the virus enters the body of elderly patients, the immune system reacts slowly or incorrectly, promoting the massive replication of the virus, inducing severe viremia and a storm of inflammatory factors, leading to immune damage of tissues and organs as well as multi-organ dysfunction [9–10]. Meanwhile, SFTSV is pansophilic and can affect multiple organs and tissues, leading to severe complications. In addition, the elderly are often most likely to develop severe complications and ultimately comorbid infections with other pathogens, such as bacteria and fungi, as severe viral infections lead to a further decline in the patient's immunity [11]. In the present study, advanced age and high viral load were independent risk factors for death in SFTS patients, which is consistent with previous studies.
Under normal conditions, procalcitoninogen (PCT) is produced by thyroid C cells and remains at low levels in plasma (< 0.5 ng/mL). Endotoxins produced by bacterial infections and cytokines produced by the body's inflammatory response are the main causes of induced PCT production and elevation [12]. In the present study, the median level of PCT was relatively low in both groups, and the median CRP was also low, indicating that endotoxin produced by bacterial infection is less likely and that inflammatory factors that cause inflammatory responses in the body may be the main cause of inducing PCT production and elevation. Some studies [13] have shown that virus-induced systemic inflammatory response syndrome can also increase PCT levels, but the elevation of PCT is not as high as in bacterial infections, and PCT can also be used for prognostic assessment of viral infections. In this study, PCT was found to be a risk factor for death in patients with SFTS, which is consistent with previous findings.
In a study by Su Yeon Kang et al [14], increased interleukin − 10 (IL − 10) was shown to be a risk factor for death in patients with severe fever with thrombocytopenia syndrome (SFTS). A study by Ming Huang et al [15] further indicated that high levels of procalcitoninogen (PCT), interleukin − 6 (IL − 6), IL − 10, tumor Tumor necrosis factor-alpha (TNF-alpha), activated partial thromboplastin time (APTT), prothrombin time (TT), and the occurrence of hemophagocytic lymphohistiocytosis were all indicators of poor prognosis in SFTS. A study by Hou H et al [16] also confirmed that calcitonin and interleukin-10 were independent risk factors for predicting the prognosis of poor prognosis in SFTS patients. In addition, a study by Zhiquan He et al [17] indicated that serum levels of interleukin-6 (IL-6), IL-10, gamma-interferon-inducible protein-10 (IP-10), and monocyte chemotactic protein-1 (MCP-1) could reflect the severity of the disease. These findings provide important biomarkers for clinical management and prognostic assessment of SFTS patients.
In this study, we showed that the early warning model included four indicators: age, viral load, PCT, and IL-10, which is consistent with the early warning indicators reported in previous studies [15–16]. The calibration curves of the prognostic nomogram model for patients with fever with thrombocytopenia syndrome (SFTS) can be concluded that the model has a good predictive and discriminative effect, and the predictive effect of the model has a high degree of overlap with the actual prognosis of the patients. Meanwhile, the nomogram constructed in this study uses high-scoring and low-scoring line segments to transform complex regression equations into simple and intuitive line segments, which improves the practical value [18].
In addition, this paper is only a single-center retrospective study, and prospective studies such as multicenter studies and case-cohort studies have not been conducted. Only the first laboratory indicators at the time of patient admission were collected, and the experimental data were not continuously and dynamically monitored for changes. The sample size selected was relatively small and there were limitations in that the severity of the cases and the prognosis of the different age groups were not stratified and analyzed. In addition, this study did not use actual data to validate the predictive effect, and no prospective study was conducted to validate the predictive effect of the model. In future studies, it is expected that more indicators affecting disease changes will be found, large-sample, multicenter prospective studies will be conducted, and the accuracy and stability of the model will be continuously improved.
In conclusion, by retrospectively analyzing the clinical data of 207 patients with novel Bunyaviruses, this study constructed a prognostic risk warning model for patients with novel Bunyaviruses and concluded that high age, high viral nucleic acid load, high procalcitoninogen (PCT), and high interleukin-10 (IL-10) were the independent risk factors for death in SFTS patients. The model has a good predictive effect and clinical utility and provides a specific basis for clinical staff to judge the prognosis of patients. In clinical practice, special attention should be paid to the levels of viral load and inflammatory indicators in elderly SFTS patients for early intervention to prevent adverse outcomes.