The prospective evaluation of viral loads in patients with severe fever with thrombocytopenia syndrome

A nomogram and heat map based on LASSO-Cox regression for predicting the risk of early-stage severe fever with thrombocytopenia syndrome patients developing into critical illness at 7-day and 14-day

Severe fever with thrombocytopenia syndrome (SFTS) represents an emerging infectious disease characterized by a substantial mortality risk. Early identification of patients is crucial for effective risk assessment and timely interventions. In the present study, least absolute shrinkage and selection operator (LASSO)-Cox regression analysis was conducted to identify key risk factors associated with progression to critical illness at 7-day and 14-day. A nomogram was constructed and subsequently assessed for its predictive accuracy through evaluation and validation processes. The risk stratification of patients was performed using X-tile software. The performance of this risk stratification system was assessed using the Kaplan-Meier method. Additionally, a heat map was generated to visualize the results of these analyses. A total of 262 SFTS patients were included in this study, and four predictive factors were included in the nomogram, namely viral copies, aspartate aminotransferase (AST) level, C-reactive protein (CRP), and neurological symptoms. The AUCs for 7-day and 14-day were 0.802 [95% confidence interval (CI): 0.707-0.897] and 0.859 (95% CI: 0.794-0.925), respectively. The nomogram demonstrated good discrimination among low, moderate, and high-risk groups. The heat map effectively illustrated the relationships between risk groups and predictive factors, providing valuable insights with high predictive and practical significance.

Red Blood Cell Distribution Width Predicts Mortality in Hospitalized Patients with Severe Fever with Thrombocytopenia Syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging epidemic infectious disease with high mortality rate. This study aimed to investigate the association of red blood cell distribution width (RDW) and mortality risk in hospitalized SFTS patients.

Methods

Clinical data of SFTS patients was retrospectively collected from three hospitals between October 2010 and August 2022. Cox proportional hazards model was used to identity the risk factors for fatal outcome. The predictive value of RDW for fatal outcome was evaluated by the receiver operating characteristic (ROC) analysis and Kaplan-Meier methods.

Results

Of 292 patients, the median age was 61.5 years. Non-survivors showed higher RDW value than survivors (13.6% vs.13.0%, P < 0.001). The mortality rate was 44.8% in patients with elevated RDW compared to 18.4% of patients with normal RDW, with a relative risk (RR) of 2.439. Elevated RDW was an independent risk factor of mortality (hazards ratio: 1.167, P = 0.019). Patients with elevated RDW had a higher cumulative mortality than patients with normal RDW. The area under the ROC curve (AUC) of RDW for the prediction of mortality was 0.690 (P < 0.001).

Conclusion

Elevated RDW was associated with higher mortality risk for patients hospitalized for SFTS. RDW may be helpful for risk stratification in SFTS patients.

Increased cTnI Predicts Early Death in Patients with Severe Fever with Thrombocytopenia: A Multicenter Study in North China

Background

Myocardial injury is common in severe fever with thrombocytopenia syndrome (SFTS) patients. Currently, research on the prognostic value of cardiac troponin I (cTnI) for predicting the mortality of SFTS patients, especially death within 7 days is limited.

Methods

Between May 2011 and October 2022, clinical and laboratory data on admission of consecutive SFTS cases were collected from six medical centres in China. The clinical endpoint was in-hospital all-cause death within seven days. Risk factors of myocardial injury and death were analysed using multivariable regression models. Prognostic models were established using Cox regression and performance of indicators was evaluated in terms of calibration, discrimination.

Results

A total of 1379 laboratory-confirmed patients were enrolled, in which 686 subjects were included for analysis. The median age was 66 years, with 48.1% of male. Eighty-seven patients died within seven days and 396 patients diagnosed with myocardial injury during hospitalization. Non-survivors had significant higher levels of cardiac indices than survivors, including cTnI, aspartic transaminase (AST) and lactate dehydrogenase (LDH). Elevated levels of cTnI (HR = 1.058, 95% CI:1.032-1.085), AST (HR = 1.191, 95% CI:1.150-1.234) and LDH (HR = 1.019, 95% CI:1.009-1.029) predicted risk of early in-hospital mortality. cTnI model performed best, with area under curve of 0.850 (0.774-0.926) and concordance index of 0.842, respectively. Statistical differences were found between high and low levels of cTnI for mortality (P<0.001) using 0.35 ng/mL as the optimal cut-off.

Conclusion

The risk of early in-hospital death can be predicted by cTnI. Clinical doctors should remind vigilant concerning the elevation of cardiac enzyme as soon as possible.

Clinical Factors Associated with SFTS Diagnosis and Severity in Cats

Severe fever with thrombocytopenia syndrome (SFTS) is a potentially fatal tick-borne zoonosis caused by SFTS virus (SFTSV). In addition to tick bites, animal-to-human transmission of SFTSV has been reported, but little is known about feline SFTSV infection. In this study, we analyzed data on 187 cats with suspected SFTS to identify biomarkers for SFTS diagnosis and clinical outcome. Body weight, red and white blood cell and platelet counts, and serum aspartate aminotransferase and total bilirubin levels were useful for SFTS diagnosis, whereas alanine aminotransferase, aspartate aminotransferase and serum SFTSV RNA levels were associated with clinical outcome. We developed a scoring model to predict SFTSV infection. In addition, we performed a phylogenetic analysis to reveal the relationship between disease severity and viral strain. This study provides comprehensive information on feline SFTS and could contribute to the protection of cat owners, community members, and veterinarians from the risk of cat-transmitted SFTSV infection.

Correlation between the Cycle Threshold Values in Detection of Severe Fever with Thrombocytopenia Syndrome Virus Using PowerChekTM SFTSV Real-Time PCR Kit and Viral Load: Prognostic Implications

BACKGROUND

This study aimed to analyze the correlation between the cycle threshold (Ct) values of severe fever with thrombocytopenia syndrome (SFTS) virus small (S) and middle (M) segments and the SFTS viral load, aiming to estimate the initial viral load and predict prognosis in the early clinical course.

METHOD

A retrospective study was conducted with confirmed SFTS patients at Jeju National University Hospital (2016-2022). Patients were categorized into non-fatal and fatal groups.

RESULTS

This study included 49 patients with confirmed SFTS (non-fatal group, n = 42; fatal group, n = 7). A significant negative correlation (-0.783) was observed between the log SFTS viral load and Ct values (p < 0.001). This negative correlation was notably stronger in the fatal group (correlation coefficient -0.940) than in the non-fatal group (correlation coefficient -0.345).

CONCLUSION

In this study, we established a correlation between SFTS viral load and Ct values for estimating the initial viral load and early predicting prognosis. These results are expected to offer valuable insights for SFTS patient treatment and prognosis prediction.

Visual analysis of global hemorrhagic fever with renal syndrome research from 1980 to 2022: Based on CiteSpace and VOSviewer

OBJECTIVE

The development and current state of hemorrhagic fever with renal syndrome (HFRS) over the past 40 years are analyzed in this study, along with explored and discovered the hotspots and frontiers in the field, which serve as the foundation for future investigation.

METHODS

CiteSpace and VOSviewer analysis software were used to visually analyze the literature data on HFRS from 1980 to 2022, including the annual number of publications, countries and research institutions, authors, co-cited literature and keywords.

RESULTS

The number of pertinent papers published in the field of HFRS displayed an overall upward trend from 1980 to 2022. The United States, China, Germany, Sweden, and France are the top 5 countries in terms of publishing volume, with high intermediate centrality mainly concentrated in Europe and the United States. The top 10 co-occurring keywords were hemorrhagic fever, renal syndrome, infection, virus, epidemic, nephropathia epidemical, disease, hantavirus, outbreak, and transmission. According to keyword cluster analysis, there were 4 main research fields. In the HFRS-related study, there were mainly 21 notable keywords and "Korean hemorrhagic fever" had the highest hemorrhagic value (28.87).

CONCLUSION

The United States, China, Germany, Sweden and other countries attached great importance to the HFRS-related research. Moreover, the collaboration between authors and institutions in various collaborator clusters should be strengthened. In recent decades, investigations have focused on the study of viral infection and the clinical symptoms and pathophysiology of HFRS. Future research may concentrate on factors affecting host population distribution and density, such as vaccine development and meteorological factors pertaining to virus transmission.

Evaluation of reverse transcription loop-mediated isothermal amplification assay for the detection of severe fever with thrombocytopenia syndrome in clinical laboratories: A single-center study

Severe fever with thrombocytopenia syndrome (SFTS) is an acute infectious disease prevalent in East Asia with a high mortality rate (5%-30%). Reverse transcription loop-mediated isothermal amplification (RT-LAMP), a rapid nucleic acid-based diagnostic technique, is a useful alternative for the clinical diagnosis of SFTS, particularly in resource-limited hospitals or rural clinics in SFTS virus-endemic regions. However, the actual clinical sensitivity and specificity of RT-LAMP remain unclear. This study evaluated the field application of RT-LAMP. This prospective field study included 130 patients with laboratory-confirmed SFTS from Yantai, Shandong Province, China. Two sets of RT-LAMP primers were validated, and one set of RT-LAMP assays was optimized for field detection. Nucleic acids of serially collected serum/plasma samples were identified using quantitative reverse transcription polymerase chain reaction (RT-qPCR) and RT-LAMP. In laboratory tests, we optimized the detection time of primer set 2 for the RT-LAMP to 60 min. Notably, the onsite testing of 279 plasma samples from patients with SFTS revealed that the sensitivity and specificity of the test were 81.9% and 96.3%, respectively. We also analyzed samples with different durations of the disease, and our study showed that the sensitivity of RT-LAMP detection at the beginning of admission was 89.92%. Univariate analysis showed that the detection rate of RT-LAMP was similar to that of RT-qPCR in the first 5 days of the disease course and was lower than that of RT-qPCR on Days 6 and 14-15 of the disease course. The positive detection rate in patients aged ≥ 65 years was significantly higher than that in younger age groups. RT-LAMP is a simple, suitable, and rapid clinical detection method of SFTS onsite screening. It is more suitable for screening patients in the early stages of the disease and analyzing samples obtained from patients aged ≥ 65 years before the 6th day of the disease course.

Clinical characteristics and outcomes of acute kidney injury in patients with severe fever with thrombocytopenia syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonosis caused by a novel bunyavirus. Until recently, the SFTS related acute kidney injury (AKI) was largely unexplored. This study aimed to investigate the clinical characteristics and outcomes of AKI in patients with SFTS.

Methods

The non-AKI and AKI groups were compared in terms of general characteristics, clinical features, laboratory parameters and cumulative survival rate. The independent risk factors for in-hospital mortality in patients with SFTS were analyzed by multivariate logistic regression to identify the population with poor prognosis.

Results

A total of 208 consecutive patients diagnosed with SFTS were enrolled, including 153 (73.6%) patients in the non-AKI group and 55 (26.4%) patients in the AKI group. Compared with patients without AKI, patients with AKI were older and had a higher frequency of diabetes. Among these laboratory parameters, platelet count, albumin and fibrinogen levels of patients with AKI were identified to be significantly lower than those of patients without AKI, while ALT, AST, ALP, triglyceride, LDH, BUN, uric acid, creatine, Cys-C, β2-MG, potassium, AMY, lipase, CK-MB, TnI, BNP, APTT, thrombin time, D-dimer, CRP, IL-6, PCT and ESR levels were significantly higher in patients with AKI. A higher SFTS viral load was also detected in the AKI patients than in the non-AKI patients. The cumulative survival rates of patients at AKI stage 2 or 3 were significantly lower than those of patients without AKI or at AKI stage 1. However, there was no significant difference in the cumulative survival rates between patients without AKI and those with stage 1 AKI. Univariate and multivariate binary logistic regression analyses demonstrated that stage 2 or 3 AKI was an independent risk factor for in-hospital mortality in patients with SFTS.

Conclusion

AKI is associated with poor outcomes in patients with SFTS, especially patients at AKI stage 2 or 3, who generally have high mortality. Our findings support the importance of early identification and timely treatment of AKI in patients with SFTS.

A new model for predicting the outcome and effectiveness of drug therapy in patients with severe fever with thrombocytopenia syndrome: A multicenter Chinese study

BACKGROUND

There are a few models for predicting the outcomes of patients with severe fever with thrombocytopenia syndrome (SFTS) based on single-center data, but clinicians need more reliable models based on multicenter data to predict the clinical outcomes and effectiveness of drug therapy.

METHODOLOGY/PRINCIPAL FINDINGS

This retrospective multicenter study analyzed data from 377 patients with SFTS, including a modeling group and a validation group. In the modeling group, the presence of neurologic symptoms was a strong predictor of mortality (odds ratio: 168). Based on neurologic symptoms and the joint indices score, which included age, gastrointestinal bleeding, and the SFTS virus viral load, patients were divided into double-positive, single-positive, and double-negative groups, which had mortality rates of 79.3%, 6.8%, and 0%, respectively. Validation using data on 216 cases from two other hospitals yielded similar results. A subgroup analysis revealed that ribavirin had a significant effect on mortality in the single-positive group (P = 0.006), but not in the double-positive or double-negative group. In the single-positive group, prompt antibiotic use was associated with reduced mortality (7.2% vs 47.4%, P < 0.001), even in individuals without significant granulocytopenia and infection, and early prophylaxis was associated with reduced mortality (9.0% vs. 22.8%, P = 0.008). The infected group included SFTS patients with pneumonia or sepsis, while the noninfected group included patients with no signs of infection. The white blood cell count and levels of C-reactive protein and procalcitonin differed significantly between the infection and non-infection groups (P = 0.020, P = 0.011, and P = 0.003, respectively), although the absolute difference in the medians were small.

CONCLUSIONS/SIGNIFICANCE

We developed a simple model to predict mortality in patients with SFTS. Our model may help to evaluate the effectiveness of drugs in these patients. In patients with severe SFTS, ribavirin and antibiotics may reduce mortality.

Clinical laboratory parameters and fatality of Severe fever with thrombocytopenia syndrome patients: A systematic review and meta-analysis

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease with high case fatality rate. Unfortunately, no vaccine or antiviral specifically targeting SFTS virus (SFTSV) are available for the time being. Our objective was to investigate the association between clinical laboratory parameters and fatality of SFTS patients.

Methods

The systematic review was conducted in accordance with The Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines. We searched (from inception to 24th February 2022) Web of Science, PubMed, National Knowledge Infrastructure databases and Wan Fang Data for relevant researchers on SFTS. Studies were eligible if they reported on laboratory parameters of SFTS patients and were stratified by clinical outcomes. A modified version of Newcastle-Ottawa scale was used to evaluate the quality of included studies. Standardized mean difference (SMD) was used to evaluate the association between laboratory parameters and outcomes. The between-study heterogeneity was evaluated quantitatively by standard Chi-square and the index of heterogeneity (I2). Heterogeneity was explored by subgroup and sensitivity analyses, and univariable meta-regression. Publication bias was determined using funnel plots and Egger’s test.

Results

We identified 34 relevant studies, with over 3300 participants across three countries. The following factors were strongly (SMD>1 or SMD<-0.5) and significantly (P<0.05) associated mortality: thrombin time (TT) (SMD = 1.53), viral load (SMD = 1.47), activated partial-thromboplastin time (APTT) (SMD = 1.37), aspartate aminotransferase (AST) (SMD = 1.19), lactate dehydrogenase (LDH) (SMD = 1.13), platelet count (PLT) (SMD = -0.47), monocyte percentage (MON%) (SMD = -0.47), lymphocyte percentage (LYM%) (SMD = -0.46) and albumin (ALB) (SMD = -0.43). Alanine aminotransferase, AST, creatin phosphokinase, LDH, PLT, partial-thromboplastin time and viral load contributed to the risk of dying of SFTS patients in each subgroup analyses. Sensitivity analysis demonstrated that the results above were robust.

Conclusions/significance

The abnormal levels of viral load, PLT, coagulation function and liver function, significantly increase the risk of SFTS mortality, suggesting that SFTS patients with above symptoms call for special concern.

Viral Load as a Factor Affecting the Fatality of Patients Suffering from Severe Fever with Thrombocytopenia Syndrome

The clinical characteristics and the effect of viral RNA loads on fatality in 56 patients with severe fever with thrombocytopenia syndrome (SFTS) were analyzed. The non-survival group (12 patients) demonstrated a significantly higher mean age (77 years) than the survival group (44 patients, 65 years) (p = 0.003). The survival rates were 91.7% and 8.3% in patients with Ct values ≥30 and differed significantly (p = 0.001) in the survival and non-survival groups, respectively. The survival rates were 52.4% and 47.6% in patients with viral copy numbers ≥10,000 and 94.3% and 5.7% in patients with viral copy numbers <10,000 in the survival and non-survival groups, respectively (p = 0.001). In a multivariate analysis, viral copy numbers and initial Acute Psychologic Assessment and Chronic Health Evaluation II (APACHE II) scores were identified as the factors affecting fatality (p = 0.015 and 0.011, respectively). SFTS viral RNA loads can be useful markers for the clinical prediction of mortality and survival.

Epidemiology, clinical characteristics, and treatment of severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by a novel phlebovirus (SFTS virus, SFTSV) in the family Phenuiviridae of the order Bunyavirales. The disease causes a wide spectrum of clinical signs and symptoms, ranging from mild febrile disease accompanied by thrombocytopenia and/or leukocytopenia to hemorrhagic fever, encephalitis, multiple organ failure, and death. SFTS was first identified in China and was subsequently reported in South Korea and Japan. The case-fatality rate ranges from 2.7% to 45.7%. Older age has been consistently shown to be the most important predictor of adverse disease outcomes. Older age exacerbates disease mainly through dysregulation of host immune cells and uncontrolled inflammatory responses. Tick-to-human transmission is the primary route of human infection with SFTSV, and Haemaphysalis longicornis is the primary tick vector of SFTSV. Despite its high case-fatality rate, vaccines and antiviral therapies for SFTS are not currently available. The therapeutic efficacies of several antiviral agents against SFTSV are currently being evaluated. Ribavirin was initially identified as a potential antiviral therapy for SFTS but was subsequently found to inefficiently improve disease outcomes, especially among patients with high viral loads. Favipiravir (T705) decreased both time to clinical improvement and mortality when administered early in patients with low viral loads. Anti-inflammatory agents including corticosteroids have been proposed to play therapeutic roles. However, the efficacy of other therapeutic modalities, such as convalescent plasma, is not yet clear.

Plasma Exchange Did Not Reduce Viral Load in a Recovered Case of Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by the SFTS virus (SFTSV). There is no specific treatment for SFTS, although several reports have indicated that plasma exchange (PE) can be an effective therapy for severe SFTS. However, whether or not PE can reduce the viral load is unclear. We herein report a woman with SFTS who had her SFTSV viral load measured just before and after PE. While the patient recovered, there was no significant difference in the SFTSV viral load after PE. Our results confirmed that PE itself does not reduce the SFTSV viral load.

Single-cell landscape of peripheral immune responses to fatal SFTS

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high fatality. Poor prognosis of SFTS has been associated with dysregulated host immunity; however, the immune patterns associated with pathophysiology involving SFTS exacerbation remain unclear. Here, we show that the single-cell landscape of peripheral immune responses is reprogrammed in SFTS and characterized by monocyte shift to an intermediate type along with complement activation, perturbation of plasmablast composition, and highly exhausted T cells, all correlated with lethal consequences. We identify the overexpression of interferon (IFN)-stimulated genes across most immune cell types after SFTSV infection, which are simultaneously related to older age, high viremia, and a hyperinflammatory response. A retrospective clinical study reveals no efficiency of IFN-α in treating SFTS. These data collectively support the intermediate monocytes and IFN-I-inducible plasmablasts to be major targets for SFTS virus infection, and they indicate the pivotal role of the IFN-I response in exacerbating hyperinflammation and lethal SFTS.

Factors and outcomes in Severe Fever with Thrombocytopenia Syndrome (SFTS): A systematic review

BACKGROUND

An emerging infectious zoonosis known as Severe Fever with Thrombocytopenia Syndrome (SFTS) is discovered mainly in Japan, South Korea and China. SFTS virus (SFTSV) which is recently recognised as bunyavirus is borne by ticks such as Haemaphysalis longicornis. It has the capabilities to spread as develop clusters and become a considerable public health threat as this virus could experience rapid evolution via gene mutation. Case fatality rate has been reported up to higher than 30%. The aim of this review is to determine the associated risk factors of SFTS and its outcome.

MATERIALS AND METHODS

Literature search was conducted using online databases PubMed, ScienceDirect, and Scopus. A total of 517 records were identified from searches in PubMed, ScienceDirect, and Scopus. From the final exclusions, a total of 26 studies were included for final analysis.

RESULTS

Associated risk factors to getting SFTS infection include occupation, history of bite from a tick, biological susceptibility, and owning of domestic animal. Fatality rates apart from single case reports range from 15.1% to 50% and are contributed by various factors including delay in hospital admission, high viral load, older age group and presence of comorbid and complication.

CONCLUSION

A seroprevalence study can be conducted amongst the high-risk occupation group such as farmers and agricultural workers, as well as testing cases where viral fever is suspected but available tests for other diseases turns out negative.

Clinical Update of Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an acute febrile illness characterized by fever, leukopenia, thrombocytopenia, and gastrointestinal symptoms such as diarrhea, nausea, and vomiting resulting from infection with the SFTS virus (SFTSV). The SFTSV is transmitted to humans by tick bites, primarily from Haemaphysalis longicornis, Amblyomma testudinarium, Ixodes nipponensis, and Rhipicephalus microplus. Human-to-human transmission has also been reported. Since the first report of an SFTS patient in China, the number of patients has also been increasing. The mortality rate of patients with SFTS remains high because the disease can quickly lead to death through multiple organ failure. In particular, an average fatality rate of approximately 20% has been reported for SFTS patients, and no treatment strategy has been established. Therefore, effective antiviral agents and vaccines are required. Here, we aim to review the epidemiology, clinical manifestations, laboratory diagnosis, and various specific treatments (i.e., antiviral agents, steroids, intravenous immunoglobulin, and plasma exchange) that have been tested to help to cope with the disease.

The Differential Characteristics Between Severe Fever With Thrombocytopenia Syndrome and Hemorrhagic Fever With Renal Syndrome in the Endemic Regions

An effective differentiation between severe fever with thrombocytopenia syndrome and hemorrhagic fever with renal syndrome was attained by a model considering patients’ age, mouse/tick contact, presence of blush, low back pain, diarrhea, enlarged lymph nodes, and white blood cell count.

Natural severe fever with thrombocytopenia syndrome virus infection in domestic cats in Japan

Severe fever with thrombocytopenia syndrome (SFTS) is a recently discovered emerging infectious disease. A zoonotic disease with a high fatality rate in human beings, clinical information on SFTS virus (SFTSV) infection in animals is important. Since 2017, we have diagnosed 24 client-owned cats living in western Japan with SFTS, by genetic and serological testing. In this study, we characterized the clinical features of SFTS in cats and their associated risk factors, by evaluating the clinical parameters retrospectively. A phylogenetic analysis on SFTSV was also conducted. There were no obvious tendencies in age or sex, outdoor cats were commonly at risk of SFTSV infection. All infected cats showed acute onset of clinical signs including anorexia and lethargy, while 68.2% of the cats showed fever and 41.7% showed vomiting. The case fatality rate was 62.5%. Thrombocytopenia, leukopenia, and elevated serum total bilirubin, serum amyloid A, and creatinine phosphokinase concentration were the characteristic findings in the first clinical blood examination. Phylogenic analysis revealed that regional clustered viruses infect both humans and cats. For pet owners and animal hospitals, SFTS in small animals could be an important public health issue.

A Cluster of Bunyavirus-Associated Severe Fever With Thrombocytopenia Syndrome Cases in a Coastal Plain Area in China, 2015: Identification of a Previously Unidentified Endemic Region for Severe Fever With Thrombocytopenia Bunyavirus

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a typical tick-borne, natural focal disease. The natural foci of SFTS were considered to exist in hilly and mountainous areas before 2015. A cluster of 3 patients exposed to a patient with a fulminant disease consistent with SFTS occurred from July to August 2015 in Dongtai County, which is characterized by alluvial plains; this prompted investigation.

Methods

The epidemiological, clinical, and laboratory features of 4 patients in the cluster were analyzed. Serum samples from the indigenous healthy population and native domesticated animals were collected to conduct laboratory tests, along with small wild animals and ticks.

Results

In 3 secondary case patients, high fever, thrombocytopenia and leukopenia developed within 8-13 days after contact with blood or bloody secretions from the index patient; SFTS was then diagnosed by means of reverse-transcription polymerase chain reaction. Genomic sequencing and analysis of S and L segments of 2 viral strains isolated from 2 secondary case patients showed that they shared 99.8%-99.9% homology in nucleotide sequence. The seroprevalences among indigenous healthy population, native livestock, native poultry, and small wild animals was 0.74%, 17.54%, 6.67%, and 1.12%, respectively. Three questing ticks, 61 feeding ticks, and 178 small wild animals were collected in August 2015. Survey on tick density and seasonal fluctuation in 2016 showed that ticks were active from March to October. All ticks were identified as Haemaphysalis longicornis. Severe fever with thrombocytopenia bunyavirus (SFTSV)-specific RNA was detected in the ticks collected in 2016, and the minimum SFTSV infection rate in these ticks was 0.54% (1 of 185).Wild mammals and ticks collected in August 2015 tested negative for SFTSV-specific RNA.

Conclusions

Aside from hilly or mountainous area, a coastal plain was identified as the natural foci of SFTSV in Dongtai County, China. The involvement of migration in the evolution of SFTSV might lead to a transregional transmission event of SFTSV.

Epidemiological and clinical features of laboratory-diagnosed severe fever with thrombocytopenia syndrome in China, 2011-17: a prospective observational study

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with an increasing case number and extensive geographical expansion, raising concerns locally and globally; however, the description of its clinical features needs to be addressed by large studies. We aimed to determine all the clinical features of SFTS in a large population of patients in an endemic area.

METHODS

In this prospective observational study, data were collected on patients admitted to the People's Liberation Army Hospital in Xinyang, Henan Province, China, with laboratory-diagnosed SFTS. Demographic, clinical, laboratory, and treatment data were collected for each patient, and patients were followed up within 2 weeks after discharge or discontinuation of treatment. The association between each demographic, clinical, and laboratory variable with a fatal outcome was assessed. A clinical scoring model was designed for the early prediction of a fatal outcome, and the effect of treatment on outcome was analysed.

FINDINGS

Between April 1, 2011, and Oct 31, 2017, 2096 patients with laboratory-confirmed SFTS were admitted. Mean age at admission was 61·4 years (SD 12·2) and 1239 (59%) patients were female. The case fatality rate (CFR) was 16·2% (95% CI 14·6-17·8). A higher risk was associated with being male (unadjusted odds ratio [OR] 1·45, 95% CI 1·15-1·83; p=0·002), older age (for a 10-year increase, unadjusted OR 1·82, 95% CI 1·62-2·04; p<0·0001), longer delay in admission (for every extra day taken before admission to hospital, unadjusted OR 1·18, 1·12-1·24; p<0·0001), presence of diarrhoea (adjusted OR 1·44, 1·12-1·87; p=0·005) or dyspnoea (adjusted OR 8·35, 5·97-11·69; p<0·0001), and development of haemorrhagic signs (adjusted OR 2·79, 95% CI 2·18-3·57; p<0·0001) or neurological symptoms (adjusted OR 30·26, 21·39-42·81; p<0·0001). Laboratory variables that were associated with death included abnormal concentrations of lactate dehydrogenase, aspartate aminotransferase, and blood urea nitrogen, and abnormal neutrophil percentage, which together with age and neurological symptoms were combined in the clinical scoring system. A total score of more than 8 was the optimal threshold to predict risk of death for patients who were evaluated within 6 days after symptom onset (area under the curve 0·879, 95% CI 0·855-0·902). For all participants, viraemia was a strong predictor of fatal outcome (all p<0·0001). Ribavirin therapy was effective in reducing CFR from 6·25% (15 of 240 participants) to 1·16% (two of 173 participants), but only in patients with a viral load below 1×10⁶ copies per mL (hazard ratio 9·72, 95% CI 1·30-72·87; p=0·027).

INTERPRETATION

The changing epidemiological features and high CFR of SFTS underscore the necessity of continued surveillance. Early prediction of fatal outcome can be attained by monitoring of clinical and laboratory data. Ribavirin should be applied early, with best results achieved before the viral load reaches 1 × 10⁶ copies per mL.

FUNDING

National Natural Science Foundation of China.

Estimation of the incidence of severe fever with thrombocytopenia syndrome in high endemic areas in China: an inpatient-based retrospective study

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is a severe viral disease caused by SFTSV. It is important to estimate the rate of missed SFTS diagnosis and to further understand the actual incidence in high endemic areas in China.

METHODS

This study was conducted in two high SFTS endemic provinces in 2015. Patients hospitalized in 2014 or within 1 year before investigation were selected after considering their clinical manifestations, specifically, fever, platelet, and white blood cell. During retrospective investigation, sera were collected to detect SFTSV antibodies to assess SFTSV infection. To further understand SFTSV infection, acute phase sera were detected; SFTSV infection rate among a healthy population was also investigated to determine the basic infection level.

RESULTS

In total, 246 hospitalized cases were included, including 83 cases (33.7%) with fever, thrombocytopenia and leukopenia, 38 cases (15.4%) with fever and thrombocytopenia but without leukopenia, and 125 cases (50.8%) without fever but with thrombocytopenia and leukopenia. In total, 13 patients (5.3%) were SFTSV IgM antibody-positive, 48 (19.5%) were IgG-positive. Of the 13 IgM-positive cases, 11 (84.6%) were IgG-positive (9 with titres ≥1:400). Seropositive rates of antibodies were high (8.4% for IgM and 30.1% for IgG) in patients with fever, thrombocytopenia and leukopenia. Furthermore, among IgG-positive cases in this group, 76% (19/25) of patients' IgG antibody titres were ≥1:400. Additionally, 28 of 246 cases were initially diagnosed with suspected SFTS and were then excluded, and 218 patients were never diagnosed with SFTS; the seropositive rates of IgM and IgG in these two groups were 25% and 67.9% and 2.8% and 13.3%, respectively. These rates were 64.3% and 21.4% in 14 sera collected during acute phase of the 28 cases mentioned above. Seropositive rate of SFTSV IgG was only 1.3% in the patient-matched healthy group, and no IgM antibody was detected. A preliminary estimate of 8.3% of SFTS cases were missed in SFTS high endemic provinces.

CONCLUSIONS

The actual SFTS incidence was underestimated. Effective measures such as adding a new SFTS case category - "SFTS clinical diagnosis cases" or using serological detection methods during acute phase should be considered to avoid missed diagnoses.

Kinetics of viral load and cytokines in severe fever with thrombocytopenia syndrome

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SFTS viremia persists until week 3 from the day of symptom onset.

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The concentrations of inflammatory cytokines are elevated in SFTS patients.

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IFN-α, IL-10, and IP-10 are associated with the initial cytokine storm.

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease in China, Japan, and Korea, which is characterized by high fever, thrombocytopenia, and high mortality. It is hypothesized that a cytokine storm plays an important role in the pathophysiology of SFTS. However, limited data have been published on the detailed kinetics of the viral load and cytokine profiles throughout the course of this disease.

Objectives

We investigated the patterns of changes in cytokines and viral load in SFTS patients.

Study design

During the admission period of patients, RNA was extracted from plasma and quantified by reverse transcription polymerase chain reaction. In addition, cytokine bead arrays were performed for the 18 cytokines and chemokines selected for testing.

Results

The median time from admission to the negative conversion of SFTS viremia was 17.0 days. When censored patients were found to be negative for viral load at discharge, the median duration of viral shedding was 13.0 days (95% CI, 5.4–20.6). Interferon (IFN)-α, interleukin (IL)-10, and IFN-γ-induced protein (IP)-10 concentrations significantly increased in the early course of disease and then decreased during the hospital stay. However, the concentrations of tumor necrosis factor-α, IL-1β, IL-12p40, IL-13, IL-17A, Regulated on Activation and Normally T-cell Expressed and Secreted (RANTES), and vascular endothelial growth factor (VEGF) increased during the late course of disease. Initial IP-10 levels during hospital days 1–4 were the most significantly correlated with initial viral load (r = 0.88, P < .01).

Conclusion

SFTS viremia persisted until weeks 2–3 and was highly correlated with initial plasma IP-10 levels. In addition, IFN-α, IL-10, and IP-10 were associated with the initial cytokine storm in SFTS.

A scoring model for predicting prognosis of patients with severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging epidemic infectious disease caused by the SFTS bunyavirus (SFTSV) with an estimated high case-fatality rate of 12.7% to 32.6%. Currently, the disease has been reported in mainland China, Japan, Korea, and the United States. At present, there is no specific antiviral therapy for SFTSV infection. Considering the higher mortality rate and rapid clinical progress of SFTS, supporting the appropriate treatment in time to SFTS patients is critical. Therefore, it is very important for clinicians to predict these SFTS cases who are more likely to have a poor prognosis or even more likely to decease. In the present study, we established a simple and feasible model for assessing the severity and predicting the prognosis of SFTS patients with high sensitivity and specificity. This model may aid the physicians to immediately initiate prompt treatment to block the rapid development of the illness and reduce the fatality of SFTS patients.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by a novel SFTS bunyavirus (SFTSV) with an estimated high case-fatality rate. However, there is no specific antiviral therapy for SFTSV infection. Symptomatic treatment and supportive therapy are the most essential part of case management. It is very important for clinicians to identify critical patients at admission. In this study, we established a simple and feasible scoring system for assessing the severity and predicting the prognosis of SFTS patients with objective parameters. This model may help the physicians to perform intervention measures in advance, control the disease progression and improve the prognosis.

Correlation of cytokine level with the severity of severe fever with thrombocytopenia syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) was an emerging hemorrhagic fever that was caused by a tick-borne bunyavirus, SFTSV. Although SFTSV nonstructural protein can inhibit type I interferon (IFN-I) production Ex Vivo and IFN-I played key role in resistance SFTSV infection in animal model, the role of IFN-I in patients is not investigated.

Methods

We have assayed the concentration of IFN-α, a subtype of IFN-I as well as other cytokines in the sera of SFTS patients and the healthy population with CBA (Cytometric bead array) assay.

Results

The results showed that IFN-α, tumor necrosis factor (TNF-α), granulocyte colony-stimulating factor (G-CSF), interferon-γ (IFN-γ), macrophage inflammatory protein (MIP-1α), interleukin-6 (IL-6), IL-10, interferon-inducible protein (IP-10), monocyte chemoattractant protein (MCP-1) were significantly higher in SFTS patients than in healthy persons (p < 0.05); the concentrations of IFN-α, IFN-γ, G-CSF, MIP-1α, IL-6, and IP-10 were significant higher in severe SFTS patients than in mild SFTS patients (p < 0.05).

Conclusion

The concentration of IFN-α as well as other cytokines (IFN-γ, G-CSF, MIP-1α, IL-6, and IP-10) is correlated with the severity of SFTS, suggesting that type I interferon may not be significant in resistance SFTSV infection in humans and it may play an import role in cytokine storm.

Score risk model for predicting severe fever with thrombocytopenia syndrome mortality

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging epidemic infectious disease with high mortality in East Aisa, especially in China. To predict the prognosis of SFTS precisely is important in clinical practice.

Methods

From May 2013 to November 2015, 233 suspected SFTS patients were tested for SFTS virus using RT-PCR. Cox regression model was utilized to comfirm independent risk factors for mortality. A risk score model for mortality was constructed based on regression coefficient of risk factors. Log-rank test was used to evaluate the significance of this model.

Results

One hundred seventy-four patients were confirmed with SFTS, of which 40 patients died (23%). Baseline age, serum aspartate aminotransferase (AST) and serum creatinine (sCr) level were independent risk factors of mortality. The area under ROC curve (AUCs) of these parameters for predicting death were 0.771, 0.797 and 0.764, respectively. And hazard ratio (HR) were 1.128, 1.002 and 1.013, respectively. The cutoff value of the risk model was 10. AUC of the model for predicting mortality was 0.892, with sensitivity and specificity of 82.5 and 86.6%, respectively. Log-rank test indicated strong statistical significance (ײ = 88.35, p < 0.001).

Conclusions

This risk score model may be helpful to predicting the prognosis of SFTS patients.

Decreased myeloid dendritic cells indicate a poor prognosis in patients with severe fever with thrombocytopenia syndrome

OBJECTIVES

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerging infectious disease caused by a novel bunyavirus in which host immune system suppression is thought to be crucial in the development of disease. This study was designed to study the frequencies and activation status of dendritic cells (DCs) at different stages of SFTS and their association with disease severity.

METHODS

All confirmed SFTS patients (N=115) were recruited from the Wuhan Union Hospital in 2015; routine laboratory parameters were collected. The frequencies, phenotypes, and subsets of circulating DCs, including myeloid and plasmacytoid dendritic cells (mDCs and pDCs), were analyzed by flow cytometry. Serum levels of interleukin (IL)-6, IL-10, and tumor necrosis factor alpha (TNF-α) were detected by ELISA. The laboratory parameters and other clinical events related to mortality were assessed by multivariate logistic regression analysis and receiver operating characteristic (ROC) curves.

RESULTS

The frequency of circulating mDCs, especially from day 9 after disease onset, could serve as a valuable prognostic biomarker for the outcome in SFTS patients (area under the curve=0.929, p<0.0001). In addition, persistent down-regulation of the co-stimulatory molecules CD80/CD86 on the mDCs was observed during the disease process. Moreover, levels of mDCs were inversely correlated with the production of IL-6, IL-10, and TNF-α and with viral load at admission.

CONCLUSIONS

The present results indicate that DCs might be functionally impaired in SFTS. A decreased level of circulating mDCs was closely correlated with the severity of SFTS.