Clinical Characteristics, Antimicrobial Resistance, and Outcomes of Patients with Invasive Pneumococcal Disease in Ningxia Hui Autonomous Region, China, 2013–2021

Objectives This study aimed to analyze the clinical features, antibiotic susceptibility profiles, and outcomes of patients with invasive pneumococcal disease (IPD) at a hospital in Ningxia Hui Autonomous Region, to provide the basis for improving the clinical treatment effect. Methods Patients with IPD were retrospectively collected from 2013 to 2021. Clinical manifestations, laboratory tests, antimicrobial susceptibility, antibiotic treatment, and outcomes of the disease were analyzed. Results In this study, we identified 127 IPD cases, of whom 49 (38.6%) had meningitis and 78 (61.4%) had bacteremia. The median ages of pediatric cases and adult cases were 2 years (IQR: 0–5) and 52.5 years (IQR: 35–62), respectively. There were 27 and 45 males in the pediatric and adult groups, and no significant gender difference in the different age groups (p = 0.584) was found. Of 75 cases with underlying diseases, pneumonia (11%), malignancy (11%), hypertension (9.4%), and hepatic cirrhosis (7.9%) were the most common. The incidence of underlying diseases was even higher in the adult group (67.1%) than in the pediatric group (47.1%) (p = 0.028). The frequency of fever, cough, and seizures was significantly higher in the pediatric group than in the adult group, with p-values of 0.004, 0.004, and 0.001, respectively. The percentage of neutrophils in the blood was significantly higher in the adult cases than in the pediatric cases (p  <  0.001). Furthermore, there was a significantly higher WBC count (p  <  0.001), percentage of neutrophils (p = 0.012), and protein level (p = 0.019) in the CSF samples in the adult patients compared to pediatric patients. The susceptibility rates of S. pneumoniae isolates to vancomycin, linezolid, and levofloxacin were 100%. The susceptibility rates of penicillin were 98.7% and 34.1% in bacteremia and meningitis patients, respectively. Most isolates were resistant to erythromycin, clindamycin, tetracycline, and azithromycin. The most common antibiotic treatment was β-lactams. Seven (5.5%) patients died during hospitalization, and 38 (29.9%) patients' health deteriorated. Conclusion These results may provide a reference basis for the diagnosis and empiric treatment of IPD in the region.


Background
Streptococcus pneumoniae (S. pneumoniae) is a Grampositive opportunistic pathogen that colonizes the upper respiratory tract of humans. S. pneumoniae is carried by up to 27%-65% of children and 10% of adults [1,2]. Tis asymptomatic colonization can progress to a broad spectrum of diseases ranging from mild noninvasive disease to life-threatening invasive pneumococcal disease (IPD) [3,4]. IPD refers to the isolation of S. pneumoniae from normally sterile sites such as blood and cerebrospinal fuid [5]. Te most severe form of IPD mainly includes meningitis and bacteremia. Infected people were mainly children, the elderly, and people with various underlying illnesses. Pneumococcal meningitis and bacteremia are important causes of high morbidity and mortality in the world [6]. Coronas et al. reported that the IPD incidence ranged from 2.4 to 3.0/ 100,000 in children under 18 years of age and from 9.5 to 15.9/100,000 in children under 2 years of age [7]. Meanwhile, it has been reported that IPD has a high mortality rate from 9.6% for those aged 17-54 years to 31.7% for those aged ≥ 75 years [8]. Te Global Invasive Bacterial Vaccine-Preventable Diseases (IB-VPD) Surveillance Network group reported that the case fatality ratio of pneumococcal meningitis was 12.2% for children < 5 years of age [9]. An eleven years study in India showed that the overall fatality rate of IPD was 17.8%, and 24.3% and 18.4% for meningitis and septicemia, respectively [10]. In 2015, there were estimated to be 83,900 cases and 37,900 deaths in children caused by pneumococcal meningitis worldwide [11].
An analysis showed that prognostic factors for mortality in IPD in adults were age, nosocomial infection, septic shock, underlying chronic diseases, solid organ tumors, immunosuppressed status, and alcohol abuse [12]. Despite the wide adoption of pneumococcal conjugate vaccination reducing the incidence of IPD, the overall mortality rate from IPD has remained high, and the antibiotic resistance in S. pneumoniae is increasing [13]. A study conducted in diferent cities in northern China reported the percentage of penicillin-resistant S. pneumonia (PRSP) from invasive pneumococcal isolates was 56.7% [14]. A multicenter study from China revealed that 67.7% of the isolates were classifed as PRSP based on meningitis (R ≥ 0.12 μg/ml) breakpoint [15]. A study of children with IPD in Beijing, China between 2012 and 2017 showed the nonsusceptibility rates of penicillin among nonmeningitis patients increased from 31.3% in 2012 to 68.2% in 2017, and the nonsusceptibility rates of meningitis isolate fuctuated by year [16]. Tese fndings suggest that the antibiotic resistance of S. pneumoniae in China is a serious public health problem.
However, there are few studies reported the clinical characteristics of patients with meningitis and bacteremia to S. pneumoniae, and the antibiotic resistance of S. pneumoniae in Ningxia Hui Autonomous Region (NHAR), which is a small landlocked autonomous region in northwestern China. Te purpose of this study was to investigate the clinical characteristics, the outcomes of patients with pneumococcal meningitis and bacteremia, and antibiotic resistance of S. pneumonia isolates at a teaching hospital in NHAR.

Patients and Defnition.
Te clinical records of all patients with positive blood and/or cerebral spinal fuid (CSF) cultures for S. pneumoniae at the General Hospital of Ningxia Medical University in NHAR from January 2013 to December 2021 were reviewed retrospectively. Isolate from both blood and CSF was classifed as meningitis. Tis study was approved by the ethics committee of the General Hospital of Ningxia Medical University.

Data Collection.
Te medical records were reviewed to collect the data of patients. Te study data included the following variables: demographic characteristics (age and gender), underlying diseases, clinical symptoms, length of stay in the hospital, antimicrobial treatment, and outcome. Routine laboratory tests such as peripheral white blood cell (WBC) count, neutrophil percentage, and procalcitonin (PCT) were collected. CSF WBC count, glucose level, total protein content, and chloride ion (Cl − ) level were recorded.

Statistical Analysis.
Categorical variables were presented as the number of cases and percentages and compared using Fisher's exact test. Continuous variables that did not follow a normal distribution were described as median with 25th and 75th percentiles (IQR, 25th-75th percentile), and compared using the Mann-Whitney U test. Statistical analysis was performed using GraphPad Prism software version 8 (GraphPad Software Inc., San Jose, CA, USA); a two-tailed p value <0.05 was considered to be statistically signifcant. Antimicrobial susceptibility test results were analyzed using WHONET 5.6 software.

Antibiotics Susceptibility
Testing. S. pneumoniae was isolated from blood alone in 78 patients, CSF alone in 36 patients, and both blood and CSF in 13 patients. Antimicrobial susceptibility testing results are shown in Table 3.
According to the breakpoint of CLSI guideline, no isolate was resistant to vancomycin, linezolid, and levofoxacin with 100% susceptibility rates. Te susceptibility rates of penicillin were 98.7% and 34.1% in bacteremia patients and meningitis patients, respectively. Meanwhile, 91.9% and 59.1% of isolates were sensitive to ceftriaxone in bacteremia and meningitis patients, and 87.5% and 50% to cefotaxime, respectively. Most isolates (more than 85%) were resistant to erythromycin, clindamycin, tetracycline, and azithromycin.

Antimicrobial Terapy and Outcome.
Of forty-nine patients with meningitis, 47 (95.9%) received initiated antibiotic treatment before the isolates were identifed. Te most common antibiotic was β-lactams, which was used for 46 (97.8%) patients. Tere were 20 (42.5%) patients who were treated with two kinds of antibiotics, the most common pattern is a combination of β-lactams and vancomycin. Tirty-one patients had changed antibiotics according to the susceptibility of the pathogen. Among these patients, 19 (61.29%) were treated with vancomycin in a combination with ceftriaxone or meropenem. One patient received vancomycin in combination with ceftazidime. Four patients had vancomycin or ceftriaxone alone, respectively. Of 78 patients with bacteremia, 76 (97.44%) received empiric treatment, and the antibiotics mainly included β-lactams, vancomycin, and teicoplanin. Among them, 34 patients were given the same antibiotics after the antimicrobial susceptibility test. Forty-three patients had changed antibiotics according to the susceptibility of the pathogen. Twenty-three patients were treated with two kinds of antibiotics, the most common pattern is a combination of third-generation cephalosporin or carbapenems in a combination with vancomycin or teicoplanin. Of all the 127 cases, 82 (65%) patients were treated, and 38 (29.9%) deteriorated. Te main reason for the deterioration of the disease was that patients gave up treatment. Seven patients died in the hospital, and the total mortality rate was 5.5%. Te mortality rates of bacteremia and meningitis were 6.4% and 4.08%, respectively.

Discussion
Despite the prevention efectiveness of pneumococcal conjugate vaccines having been reported in more than 50 countries [18], the high prevalence of IPD and the increasing rates of penicillin and other antibiotic resistance are still global problems. Of note, clinical presentation and antimicrobial susceptibility patterns of S. pneumoniae vary geographically. In this study, we described the clinical characteristics and treatment outcomes of patients with S. pneumonia bacteremia and meningitis and examined the antimicrobial resistance of S. pneumonia isolates from 2013 to 2021 in a teaching hospital in the northwestern region of China. Our results showed males with pneumococcal bacteremia and meningitis had a higher occurrence than females, with a male/female ratio of 1.5 : 1, whereas there was no signifcant diference among gender. Tis result is consistent with a previous study [19]. However, Geng et al.
reported that there were signifcantly more male patients than female patients [20]. In this study, the median age of all patients was 31 years and the percent of patients between <16 years and 16-60 years groups are similar (40.16% vs 40.94%), while the percentage of patients older than 60 years old is low (18.9%). Many previous studies have described a higher level of pneumococcal disease among adult patients over the age of 65 and children younger than 5 years old [21][22][23]. Tis could be explained by the fact that our hospital is a comprehensive teaching hospital that houses various specialist wards to accept more adults with underlying diseases. When we compared the subgroup in group <16 years old, we found 38 (74.5%) patients were younger than 5 years old. Te minimum age of patients in this study is 1 day, however other studies reported the minimum age was 60 days or 6 months [24,25]. Underlying diseases have been reported as the risk factors for IPD [21,26], and reported underlying diseases including myocardial infarction, cerebrovascular disease, diabetes mellitus, malignancy, and so on. Our fndings showed that 75 (59%) patients had some form of underlying diseases. Te most common underlying conditions were malignancy (11%), pneumonia (11%), hypertension (9.4%) and cirrhosis (7.9%). In parallel with previous studies, cancer patients are especially susceptible to severe pneumococcal infections, because of their weakened immune systems [27,28]. Cirrhosis is a well-known predisposing factor for IPD and cirrhosis afected 7.9% of the patients in our study. A multicenter study reported that cirrhosis increased the risk of death from IPD more than any other condition analyzed [29,30]. Te reasons for this observation have not been elucidated. Propst-Graham et al. [31] showed that increased mortality from pneumococcal pneumonia in cirrhotic rats is related to impairments in both preneutrophil-mediated and later neutrophil-mediated innate pulmonary killing of the S. pneumoniae. Moreover, the incidence of underlying diseases was signifcantly higher in the adult group than in the pediatric group. Tis can be explained by the fact that adult patients with underlying diseases have weak immune systems. Hence, researchers hypothesized that control of underlying diseases is a measure to decrease cases of pneumococcal infections [32,33].
Of the 24 (47.1%) pediatric patients with underlying diseases, the most common conditions were pneumonia and anemia. Tis fnding is inconsistent with previous studies which reported that the main underlying disease was leukemia for children with IPD [16,34]. Te underlying disease rate of children in our study was higher than in other studies in China [16,35]. While in 67.1% of adult patients who had underlying diseases, hypertension was most frequent, followed by malignancy and cirrhosis. Tsuchiya et al. reported a similar result that 15.1% of adult IPD patients had liver diseases [36].
In the present study, presenting symptoms mainly included fever, cough, vomiting, consciousness obstacle, and headache. Among all the symptoms, fever, cough, and seizures were signifcantly diferent in the two age groups,  occurring more commonly in pediatric patients. Tis fnding is in line with several previous studies in which fever was present in almost all cases of pneumococcal meningitis [37,38]. Another study has shown that a delay in the initiation of therapy introduces the potential for increased morbidity and mortality of communityacquired bacterial meningitis [39]. Tus, these fndings may suggest that patients presenting with fever and another mental status should be given empirical antibiotic therapy before the blood or CSF culture results were reported. Elevated blood WBC count and neutrophil percentage are traditionally reported to be a reliable indicator of bacterial infection. In the present study, blood WBC was elevated in 60% of pediatric cases and 52% of adult cases, respectively. Te neutrophil percentage was elevated in 46% of pediatric cases and 80% of adult cases. Nevertheless, it is important to highlight that 40% and 54% of the children, and 40% and 54% of the adults did not have elevated blood WBC counts and neutrophil percentages, suggesting that more laboratory tests should be combined to help diagnose IPD before S. pneumoniae identifcation. Bacterial meningitis is characterized by high levels of CSF WBC counts and CSF protein and decreased levels of CSF glucose [40]. Forty-nine patients with pneumococcal meningitis included in this study had routine CSF analysis. Overall, 95.9%, 93.9%, and 83.7% of patients had elevated levels of WBC counts and CSF protein and decreased levels of glucose, respectively. Inconsistent with our result, Wang et al. [38] reported that 11.5% of the children had normal CSF cell counts. Tese results emphasize the importance of a comprehensive analysis of CSF cell counts, CSF protein, and glucose levels. Additionally, WBC count, neutrophil percentage and protein level in the CSF samples were signifcantly higher in the pediatric group than in the adult group. Tis fnding may be explained that adults mount stronger immune responses than children to prevent or limit infection.
Since the clinical resistance to penicillin in S. pneumoniae was frst reported in 1965 [41], antibiotic resistance among S. pneumoniae continues to increase and become a severe problem worldwide [42]. Te high resistance rates for penicillin have been reported in many countries, such as the United States, Tunisia, France, and Spain [43][44][45]. A previous study reported that the resistance trend of S. pneumoniae was regionally diferent [46]. Te nonsusceptibility rates of penicillin in bacteremia and meningitis isolates (1.3% and 65.9%) were lower than in a study conducted in Beijing China (8.5% and 71.9%) [16]. Consistent with many studies [47][48][49], S. pneumoniae in the present study is generally sensitive to vancomycin, linezolid, and levofoxacin, with 100% susceptibility. Erythromycin, clarithromycin, and azithromycin are the three most widely used macrolide antibiotics in the clinic. In the current study, the high resistance rates to macrolide ranged from 88.9% to 91.9%, which were either similar to or higher than those reported in previous studies. A study from the Asian Network for Surveillance of Resistant Pathogens (ANSORP) revealed that resistance rates to macrolides in pneumococcal isolates ranged from 64.7% to 67.2% in Asian countries [50]. Te resistance rates of erythromycin, clindamycin, azithromycin, and tetracycline were 92%, 81.33%, and 90.67% in Shanghai, China [51]. Due to the high resistance to macrolide, the clinical utility of macrolide against infections caused by S. pneumoniae is low.
In this study, antimicrobial treatment was frequently initiated with 3-generation cephalosporin (44.88%), followed by carbapenems, vancomycin, and latamoxef. Seventy-four patients had changed antibiotics according to the susceptibility of the pathogen. Vancomycin, meropenem, and ceftriaxone were the most common antibiotics. In our study, the total mortality was 5.5%. Tis rate is lower than those described in other studies, showing a higher 30-day mortality rate, ranging from 16%-46.2% [37,38,52,53]. Tis may be because 29.9% of patients deteriorated in the hospital and gave up treatment, but we did not follow up with patients and observe the 30-day mortality rate. Our study has some limitations. Firstly, it was performed with data from only one hospital with a limited number of patients in adult and pediatric groups. Hence, data from this study may not refect the clinical characteristics of IPD in the NHAR. Due to the nature of the retrospective study, we could not confrm the information on the vaccination history of individuals and identify the capsule type of S. pneumoniae isolates. Similarly, we could not observe a 30day mortality rate, and this may result in the mortality rate in this study being lower than in other studies.

Conclusion
In conclusion, IPD is a serious infectious disease that is still endemic in the NHAR. Our results showed that IPD can occur at any age, especially the children and adults with underlying diseases. Te clinical characteristics of IPD varied with age.
Te antibiotic resistance rates are of serious concern in patients with pneumococcal meningitis, and this emphasizes the need for rapid initiation of using appropriate empiric antibiotic therapy if meningitis is suspected. Tese results may provide a reference basis for the diagnosis and empiric treatment of IPD in the region. However, due to a limited number of patients from only one hospital, large-scale multicenter surveillance of IPD should be implemented in the future.

Data Availability
Te data in this study are available from the corresponding author upon reasonable request.

Ethical Approval
All study was permitted by the ethics committee of the General Hospital of Ningxia Medical University.

Conflicts of Interest
Te authors declare that they have no conficts of interest.