Clinical features and etiology of patients with community-acquired pneumonia in southern China

Background: The aim of this study was to investigate the clinical features and etiology in patients with community-acquired pneumonia (CAP) in southern China. Methods: A total of 342 patients who presented community-acquired pneumonia (CAP) from January 2019 to December 2019 were enrolled in this study. The respiratory pathogens in nine test and loop-mediated isothermal amplication (LAMP) detection were used to identify pathogens. Results: The mean age of this study population was 60.89 ± 18.87 years. The total incidences of CAP were more prevalent in males (60.5%, 207/342) than females (39.5%, 135/342), and the percentage was 65.8% (225/342) CAP patients in summer and autumn. The main causative pathogens were identied in 96/342 (28.1 %) patients. Of these, 14 (14.6 %) were MP infection, the most frequently isolated microorganism. Bacterial infection in the single infection was present in 47 (47/96, 49.0%). Mixed infections were demonstrated in 26 (26/96, 27.1%). MRSA infection was close to patients with systemic diseases (P = 0.001). Factors that were associated with systemic disease was the age >65 (OR 5.555, 95%CI 3.402-9.071, P<0.001). Conclusions: MP is common organisms isolated in community-acquired pneumonia. The year of above 65, the count of WBC and mixed pathogens infections may be associated with an increased risk of CAP patients with systemic disease. for


Background
Community-acquired pneumonia (CAP) is a common clinical disease that ranked as the fth leading cause of mortality global [1]. It is reported that there are about 3.2 million people die from CAP each year globally, surpassing other infectious diseases, such as tuberculosis, HIV and malaria [2]. A prospective multicenter study in Asia reported that the mortality rate of CAP in Asia was as high as 7.3% [3]. Several factors are associated with the risk of CAP mortality, including in ammatory response, cardiovascular complications, and etiology [4][5][6]. Some studies identi ed age and male sex increases the incidence of CAP [7,8]. Identi cation the etiology of CAP patients remains challenging, 30-65% of patients do not have a certain pathogen isolated [9]. Streptococcus pneumoniae(S. pneumoniae) is the most frequently identi ed CAP pathogen [10]. The etiology of a large number of CAP patients is triggered by bacterial and viral microorganisms, 20-50% of CAP cases are cause by bacterial pathogens [11,12]. Viral CAP pathogens such as In uenza, respiratory syncytial virus are the most common [13]. CAP also has impact on national economic development for high consumption rates of therapy in both inpatient and outpatient. CAP patients have not been su ciently evaluated, leading to almost all patients are treated empirically because of the lack of speci cs diagnostic methods to rapidly isolate the pathogen [14].
The bacterial culture and smear microscopy are the detection of bacterial pathogen most extensively used [15]. In recent years, loop-mediated isothermal ampli cation (LAMP) have become a useful alternative to the effective detection of pathogenic micorganism. LAMP-based PCR is detection of thirteen common respiratory pathogens in patients with CAP [16,17].
Microbial cause varies by host factors and geographic location. The aim of this study is to analysize the pathogens and clinical features of patients that were diagnosed of CAP in southern China.

Methods
Study patients 342 hospitalized patients with CAP were recruited from inpatient of Meizhou People's Hospital between January 2019 to December 2019. All participants age from 13 to 99 years old in this study. Patients were diagnosed as CAP if they met one of the following clinical characteristics: (1) typical characteristics of pneumonia, which were de ned by a new in ltrate on a chest X-rays or computed tomography (CT) scan examined by radiologists. (2) one or more respiratory symptoms, including new cough, exacerbated cough with or without sputum production, fever (> 37.8 °C) or hypothermia (< 35.6 °C) [18]. Statistical analysis SPSS 21.0 software(SPSS Inc., Chicago, USA) was used for statistical analyses of the data. Descriptive data are presented as frequencies (percentages). Categorical variables were compared with the Pearson Chi-square test. Two-group comparisons of continuous variables were compared with independent samples t-test. The level of statistically signi cant was P ≤ 0.05.

Study population and clinical characteristics
In Table 1, of the 342 patients with CAP, 207 patients (60.5%)were male and 135 patients (39.5%) were female. The average age of study population was 60.89, including 197 cases were nonelderly with a mean age of 48.38 (≤ 65 years), and 145 cases were elderly with a mean age of 77.90 ( 65 years). A total of 169 patients (49.42%) had at least 1 systemic diseases disease, including coronary artery disease, cerebral infarction, diabetes, hypertension. Laboratory parameters of the white blood cell (WBC) counts (> 9.5 × 10 9 cells/L) was found in 145 cases (42.4%). Summer and autumn have more patients with CAP (108/342, 31.6%; 117/342, 34.2%) in this study.  Table 2 shows the number of every causal microorganisms.

Logistic Regression Analysis
In multivariable logistic regression analysis, > 65 years but not gender, was found to be signi cant risk factors for the patients with CAP associated with systemic disease (p < 0.001). Moreover, multiple pathogens and the counts of WBC were identi ed as independent risk factor for patients with CAP associated with systemic disease (OR 2.894, 95% CI 1.015-8.253, P = 0.047; OR 1.067, 95% CI 1.009-1.127, P = 0.022). No signi cant interaction was found between gender and smoking (P = 0.398, P = 0.654). Table 5 shows all ORs and 95% CIs.

Discussion
CAP is a predominant threat to public health worldwide. In this study of 342 hospitalized CAP patients, 28.1% CAP cases were identi ed the etiology, lower than other regions is reported [9]. Maybe some patients included in this study were treated before go to the hospital. Furthermore, some patients may have received prior antibiotics that were consistent with the guidelines, but that failed. The potential bacterial may be obscured for patients use of antibiotics prior because of comorbidities [19]. Previous studies showed that etiology remains unknown in the most of cases, indicating that identi cation of a precise pathogen diagnosis for CAP patients is challenging [20].
The characteristics of CAP pathogens distribution in different regions are different, and with the passage of time, population distribution, seasonal alternation, the use of antibiotic and other factors, the antiinfection should be based on accurate diagnosis of pathogens, but due to the precise etiology testing has not been achieved in most patients, and there is currently no consistent antibiotic treatment plan [21]. In addition, alcoholism, smoking, chronic obstructive pulmonary disease (COPD), immunode ciency, tumors, diabetes, cerebrovascular diseases and others have become risk factors of CAP, and the increase of age is closely related to the severity of CAP, which should be attached great importance to the prevention of CAP [22]. MP was the most frequently identi ed pathogens in our study. MP is a prokaryotic pleuropneumonia-like microorganism between bacteria and viruses that contains DNA and RNA and lacks the cell wall. Gram staining is negative, the diameter is 50-300 nm, the structure is simple, and it has various shapes such as sphere, rod, and lament that can pass through the bacteria lter. It is spread through close contact with infected patients with an incubation period of 1-3 weeks. It occurs more frequently in summer and autumn in the south, and more frequently in autumn and winter in the north. The prevalence of school-age children is 5-15 years old. It shows a downward trend after puberty and gradually disappears after adulthood. 25% of cases have extrapulmonary complications known as mucosal skin lesions [23].
MRSA was the most common bacterial etiology, followed by K. pneumoniae and P. aeruginosa in our identi ed cases. CAP caused by MRSA was the largest groups in our study group, with proportions of 11.5% and 15.6% in ≤ 65 years and 65 years, respectively. In addition, the percentages of bacterial pathogen infection with MRSA patients have systemic disease (21.9%) was relatively higher than patients without systemic disease group (P = 0.001). MRSA is the most common bacterial pathogen infection that gives rise to a high burden of signi cant healthcare costs, morbidity, and mortality for patients every year [24][25][26]. The percentages of bacterial pathogen infection with P. aeruginosa tested positive made up 9.4% among patients with systemic disease group (P = 0.029). We aimed to identify CAP patient characteristics associated with causative microorganisms in southern China. We found > 65, multiple pathogens and WBC are associated with a higher mortality rate; especially, above 65 years (OR 5.555, 95%CI 3.402-9.071, P < 0.001) was close associated with increased CAP patients with systemic disease mortality. Our study found that age was similar to the ndings of previous studies [27][28][29].
There are some limitations deserve consideration in our study. One was that we did not investigate a larger sample size from the same population due to the data collection limited to one year. Second, we used only two different assays for different pathogens but did not clarify the differences in detection performance between these microbiological techniques. Third, some of the individuals in this population selfmedicated with antibiotics may not be generalized to CAPs. Therefore, further studies will be needed to con rm our ndings.

Conclusions
MP is common organisms isolated in community-acquired pneumonia.