Abstract
AIM
To provide statistical evidence for the use of antibiotics in ophthalmology by assessing the distribution and antibiotic sensitivity of bacterial isolates from ocular specimens with suspected microbial infections.
METHODS
This study applied a retrospective analysis of 3690 bacterial isolates from ocular specimens, which were obtained from the conjunctiva, cornea, aqueous humor, vitreous body, and other ocular sites of the patients at Shandong Eye Institute in northern China from January 2013 to December 2017. The parameters assessed mainly included the distribution of isolated bacteria and the results of susceptibility tests for antibiotics. In the analysis of antibiotic sensitivities, the bacteria were divided into four groups according to gram staining, and statistical methods were used to compare their antibiotic sensitivities.
RESULTS
Among the 3690 isolated bacterial strains, Staphylococcus epidermidis (2007, 54.39%) accounted for the highest proportion. As for the total isolates, their sensitivity rate to gatifloxacin was up to 90.01%, with four types of gram-stained bacteria being all highly sensitive to it, but their sensitivity rate to levofloxacin was only 51.91%. The sensitivity rate of gram-negative bacilli (G-B) to levofloxacin was 83.66%, significantly higher than the other three types of gram-stained bacteria (P<0.05). Gram-positive cocci (G+C, 97.95%) and gram-positive bacilli (G+B, 97.54%) were more sensitive to vancomycin than gram-negative cocci (G-C, 70.59%) and G-B (68.57%; P<0.05). For fusidic acid, the sensitivity rates of G+C (89.83%) and G+B (73.37%) were significantly higher than that of G-B (29.83%; P<0.05). The gram-negative bacteria's sensitivity rate to cefuroxime was as low as 59.25%, but only G-B was less sensitive to cefuroxime (57.28%), while G-C was still highly sensitive (89.29%). The sensitivity rate of gram-positive bacteria to moxifloxacin was as high as 80.28%, but only G+C was highly sensitive to moxifloxacin (81.21%), while G+B was still less sensitive (32.00%).
CONCLUSION
Staphylococcus epidermidis is the predominant isolate in all ocular specimens with bacteria. Gatifloxacin is more suitable for topical prophylactic use than levofloxacin in ophthalmology when necessary. Vancomycin and fusidic acid both have better effects on gram-positive bacteria than gram-negative bacteria. More accurate antibiotic sensitivity analysis results can be obtained when a more detailed bacterial classification and more appropriate statistical methods are performed.
Keywords: bacteria, ocular infections, pathogen, antibiotic sensitivity
INTRODUCTION
Ocular bacterial infections, which are associated with many risk factors including contact lenses, trauma, surgery, age, dry eye state, chronic nasolacrimal duct obstruction and previous ocular infections[1]–[2], are common in ophthalmology and vary from self-limiting to sight-threatening[3]. In the treatment of bacterial infections, pathogenic bacteria must be identified to ensure appropriate antimicrobial treatment. Broad-spectrum antibiotics have been commonly used to treat ocular infections, but pathogenic bacteria have shown a decreased sensitivity to widely used broad-spectrum antibiotics[4]. Therefore, we retrospectively assessed the bacterial isolates from ocular specimens with suspected microbial infections in northern China, hoping to find more sensitive antibiotics for different kinds of pathogens and help ophthalmologists make effective decisions in treating ocular bacterial infections.
Pathogen distribution and antibiotic sensitivity are constantly changing over time, so it is necessary to summarize regularly. There have been many studies on antibiotic sensitivity, which were conducted according to the classification of gram-positive and gram-negative bacteria or direct enumeration of the sensitivity rates. The question whether further classifying gram-stained bacteria and comparing the sensitivity rate by a statistical analysis can lead to more accurate results in antibiotic sensitivity studies has not attracted enough attention. We did get some notable results when a detailed classification of the tested bacterial isolates and a statistical analysis of the sensitivity rate were conducted in the current study.
SUBJECTS AND METHODS
Ethical Approval
This retrospective study was approved by the Institutional Review Board of Shandong Eye Institute. Because of its retrospective nature, the requirement of informed consent was waived. All study conduct adhered to the tenets of the Declaration of Helsinki.
A retrospective review of the records of ocular isolates was conducted from January 2013 to December 2017 at Shandong Eye Institute, a major tertiary eye center in northern China. Clinical specimens were obtained from the conjunctiva, cornea, aqueous humor, vitreous body, eyelid margin, lacrimal passage, orbital contents, and other ocular sites of the patients in the Inpatient Wards and Outpatient Clinics. Cultures were performed using liquid (nutrient broth) and solid (chocolate agar, blood agar, and MacConkey agar) media. Bacterial isolates were identified, and dilution antimicrobial susceptibility testing was made and interpreted using automated microbiology systems, i.e., VITEK II compact 30 before 2016 and Microscan Walkaway 96 after 2016, at the clinical microbiology laboratory of our institution according to the Clinical and Laboratory Standards Institute's Guidelines. The parameters assessed mainly included the distribution of isolated bacteria and the results of susceptibility tests for antibiotics. Only nonrepetitive isolates that underwent susceptibility testing were included in this study, and not all antimicrobials were tested against each isolate.
Most data were collected from the Laboratory Information System used by our clinical microbiology laboratory. Positive results were inputted into a Microsoft Excel spreadsheet file, which included patient name, patient ID number, patient age, collection date, ward type, collection site, organism isolated and minimum inhibitory concentration values against various antibiotics. For a small amount of uncertain data, such as “intraoperative specimen”, the patients' medical records were checked to ensure the accurate collection site. We also obtained a five-year statistical report on the antibiotic sensitivity from the Laboratory Information System. In the analysis of antibiotic sensitivities, the bacteria were divided into four groups according to gram staining, and statistical methods were used to compare their antibiotic sensitivities.
Statistical Analysis
Data were analyzed using the SPSS (version 19.0; SPSS, Inc., Chicago, IL, USA). The spearman correlation analysis was used to study the correlation between two variables. Comparisons of categorical variables were conducted using the Chi-square test. A P-value <0.05 at 95% CI was considered statistically significant.
RESULTS
A total of 11 530 ocular specimens with suspected microbial infections were submitted for microbiological evaluation. Among these specimens, 3625 (31.44%) showed bacterial growth, and 3690 bacterial strains were isolated. The positivity rates of the bacterial cultures from years 2013 to 2017 were 30.82%, 35.26%, 25.76%, 25.88%, and 36.56%, respectively. The change in the annual culture positivity rate was not statistically significant (P=0.747). Among the patients corresponding to positive bacterial culture specimens, 1513 were male and 2112 were female, with a male-female ratio of 1:1.40. The average age of the patients was 49.65±22.21 (range 4d-102y). Among the 3625 bacterial specimens, 2849 (78.59%) were obtained from the conjunctiva, 569 (15.70%) from the cornea, and 111 (3.06%) from the aqueous humor or vitreous body. The remaining 96 (2.65%) specimens were gathered from the lacrimal passage, eyelid margin, orbital contents and other ocular sites.
The distribution of bacterial genera isolated from ocular specimens with suspected microbial infections between 2013 and 2017 is presented in Table 1. A total of 3690 strains (32 genera and 140 species) were isolated. Among these strains, 3037 were gram-positive cocci (G+C; 82.30%), 407 were gram-negative bacilli (G-B; 11.03%), 221 were gram-positive bacilli (G+B; 5.99%), and 25 were gram-negative cocci (G-C; 0.68%). The most common bacterial genera were Staphylococcus (2706, 73.33%), Corynebacterium (161, 4.36%), Neisseria (19, 0.51%), and Pseudomonas (91, 2.47%) in G+C, G+B, G-C, and G-B, with Staphylococcus epidermidis (S. epidermidis; 2007, 54.39%), Corynebacterium xerosis (160, 4.34%), Neisseria mucosa (7, 0.19%), and Pseudomonas aeruginosa (77, 2.09%) being the main isolates, respectively. The predominant bacterial isolate was S. epidermidis (2007, 54.39%), followed by Staphylococcus aureus (260, 7.05%), C. xerosis (160, 4.34%), Staphylococcus hominis (125, 3.39%), Staphylococcus haemolyticus (115, 3.12%), and P. aeruginosa (77, 2.09%). Neither the annual changes in the proportions of the above major strains nor those in the proportions of G+C, G+B, G-C, and G-B were statistically significant (P>0.05). The distribution of bacteria isolated from different ocular sites between 2013 and 2017 is presented in Table 2. S. epidermidis was the predominant bacterial isolate in the conjunctiva, cornea, aqueous humor or vitreous body, and other ocular sites, respectively. In addition, S. aureus was one of the most common bacteria in the conjunctiva, cornea, as well as aqueous humor or vitreous body.
Table 1. Distribution of bacterial genera isolated from ocular specimens with suspected microbial infections between 2013 and 2017.
| Type of bacterial isolates | Number of isolates (n=3690) | % |
| G+C | 3037 | 82.30 |
| Staphylococcus | 2706 | 73.33 |
| Streptococcus | 141 | 3.82 |
| Enterococcus | 88 | 2.38 |
| Micrococcus | 49 | 1.33 |
| Kocuria | 33 | 0.89 |
| Granulicatella | 11 | 0.30 |
| Others | 9 | 0.24 |
| G-B | 407 | 11.03 |
| Pseudomonas | 91 | 2.47 |
| Serratia | 37 | 1.00 |
| Sphingomonas | 33 | 0.89 |
| Proteus | 29 | 0.79 |
| Escherichia | 28 | 0.76 |
| Klebsiella | 27 | 0.73 |
| Acinetobacter | 25 | 0.68 |
| Enterobacter | 20 | 0.54 |
| Morganella | 19 | 0.51 |
| Haemophilus | 12 | 0.33 |
| Others | 86 | 2.33 |
| G+B | 221 | 5.99 |
| Corynebacterium | 161 | 4.36 |
| Bacillus | 33 | 0.89 |
| Actinomyces | 12 | 0.33 |
| Rothia | 7 | 0.19 |
| Arcanobacterium | 5 | 0.14 |
| Others | 3 | 0.08 |
| G-C | 25 | 0.68 |
| Neisseria | 19 | 0.51 |
| Moraxella | 6 | 0.16 |
| Total | 3690 | 100 |
Table 2. Distribution of bacteria isolated from different ocular sites between 2013 and 2017.
| Bacterial isolates from different ocular sites | Number of isolates (n=3690) | % |
| Conjunctiva | 2892 | 78.37 |
| Staphylococcus epidermidis | 1661 | 45.01 |
| Staphylococcus aureus | 213 | 5.77 |
| Corynebacterium xerose | 130 | 3.52 |
| Staphylococcus hominis | 97 | 2.63 |
| Staphylococcus haemolyticus | 97 | 2.63 |
| Staphylococcus lentus | 57 | 1.54 |
| Enterococcus faecalis | 44 | 1.19 |
| Streptococcus mitis | 27 | 0.73 |
| Pseudomonas aeruginosa | 27 | 0.73 |
| Others | 539 | 14.61 |
| Cornea | 579 | 15.69 |
| Staphylococcus epidermidis | 256 | 6.94 |
| Pseudomonas aeruginosa | 39 | 1.06 |
| Staphylococcus aureus | 34 | 0.92 |
| Corynebacterium xerose | 24 | 0.65 |
| Staphylococcus hominis | 19 | 0.51 |
| Staphylococcus haemolyticus | 16 | 0.43 |
| Micrococcus luteus | 13 | 0.35 |
| Streptococcus mitis | 11 | 0.30 |
| Others | 167 | 4.53 |
| Aqueous humor or vitreous body | 118 | 3.20 |
| Staphylococcus epidermidis | 42 | 1.14 |
| Staphylococcus aureus | 9 | 0.24 |
| Staphylococcus hominis | 6 | 0.16 |
| Bacillus subtilis | 6 | 0.16 |
| Pseudomonas aeruginosa | 5 | 0.14 |
| Bacillus cereus | 5 | 0.14 |
| Others | 45 | 1.22 |
| Other ocular sites | 101 | 2.74 |
| Staphylococcus epidermidis | 47 | 1.27 |
| Pseudomonas aeruginosa | 6 | 0.16 |
| Escherichia coli | 4 | 0.11 |
| Staphylococcus aureus | 4 | 0.11 |
| Others | 40 | 1.08 |
| Total | 3690 | 100 |
“Other ocular sites” included lacrimal passage, eyelid margin, orbital contents and so on.
The sensitivities of the bacterial isolates to the antibiotics available in our institution are shown in Table 3. The sensitivity rate of the total isolates to gatifloxacin was up to 90.01%, with G+C, G+B, G-C, and G-B being all highly sensitive. For levofloxacin, the sensitivity rate of the total isolates was only 51.91%, whereas that of G-B was 83.66%, significantly higher than that of G+C, G+B, and G-C (P<0.05). For vancomycin, the sensitivity rate of gram-positive bacteria was as high as 97.92% (3112/3178), while that of gram-negative bacteria was only 68.97% (60/87). Moreover, the sensitivity rates of G+C and G+B to vancomycin were significantly higher than those of G-C and G-B (P<0.05). For fusidic acid, the sensitivity rate of gram-positive bacteria was as high as 88.91% (2702/3039), whereas that of gram-negative bacteria was only 32.00% (64/200). In addition, the sensitivity rate of G+C to fusidic acid was significantly higher than that of G-C and G-B, and the sensitivity rate of G+B was significantly higher than that of G-B (P<0.05). For cefuroxime, the sensitivity rate of gram-negative bacteria was as low as 59.25% (269/454), but it was only G-B whose sensitivity rate was 57.28%, while the sensitivity rate of G-C was 89.29%, significantly higher than that of G-B (P=0.001). For moxifloxacin, the sensitivity rate of gram-positive bacteria was as high as 80.28% (2121/2642), but it was only G+C whose sensitivity rate was 81.21%, while the sensitivity rate of G+B was just 32.00%, significantly lower than that of G+C (P=0.000). The sensitivity ranking results of these antibiotics are shown in Table 4, and any sensitivity rate with a denominator number less than 15 was not included in this statistical analysis. Antibiotic sensitivities of fusidic acid and ciprofloxacin increased year by year (Rs=0.900, P=0.037), whereas the changes in other antibiotics were not statistically significant (P>0.05).
Table 3. Sensitivities of the antibiotics available in our institution.
| Antibiotics | Total | G+C | G+B | G-C | G-B |
| Tigecycline | 99.59 (1700/1707) | 99.59 (1681/1688) | 100.00 (11/11) | - | 100.00 (8/8) |
| Vancomycin | 97.15 (3172/3265) | 97.95 (2914/2975) | 97.54 (198/203) | 70.59 (12/17) | 68.57 (48/70) |
| Rifampicin | 94.48 (2876/3044) | 94.90 (2718/2864) | 90.84 (119/131) | 90.00 (9/10) | 76.92 (30/39) |
| Gatifloxacin | 90.01 (3044/3382) | 92.69 (2548/2749) | 91.12 (195/214) | 81.48 (22/27) | 71.17 (279/392) |
| Cefuroxime | 89.28 (3058/3425) | 94.35 (2603/2759) | 87.74 (186/212) | 89.29 (25/28) | 57.28 (244/426) |
| Fusidic acid | 85.40 (2766/3239) | 89.83 (2578/2870) | 73.37 (124/169) | 52.63 (10/19) | 29.83 (54/181) |
| Ceftazidime | 81.99 (1498/1827) | 84.41 (1056/1251) | 69.62 (110/158) | 90.91 (20/22) | 78.79 (312/396) |
| Amikacin | 81.61 (324/397) | 5.00 (2/40) | 100.00 (6/6) | 100.00 (1/1) | 90.00 (315/350) |
| Moxifloxacin | 80.30 (2123/2644) | 81.21 (2105/2592) | 32.00 (16/50) | 100.00 (1/1) | 100.00 (1/1) |
| Ofloxacin | 67.40 (2402/3564) | 66.63 (1911/2868) | 64.22 (149/232) | 78.57 (22/28) | 73.39 (320/436) |
| Gentamicin | 66.59 (2455/3687) | 65.96 (2004/3038) | 64.95 (139/214) | 56.52 (13/23) | 72.57 (299/412) |
| Tobramycin | 64.13 (2271/3541) | 63.50 (1823/2871) | 62.87 (149/237) | 75.00 (21/28) | 68.64 (278/405) |
| Levofloxacin | 51.91 (1941/3739) | 46.28 (1430/3090) | 71.30 (154/216) | 60.87 (14/23) | 83.66 (343/410) |
| Ciprofloxacin | 44.61 (1793/4019) | 43.36 (1329/3065) | 26.86 (137/510) | 60.00 (15/25) | 74.46 (312/419) |
“-” means no antibiotic susceptibility testing was conducted.
%
Table 4. Sensitivity ranking results of the antibiotics.
| Stains | Sensitivity ranking (P<0.05) |
| Total | TGC>VAN>RIF>GAT, CXM>FDA>CAZ, AMK, MFX>OFX, GEN>TOB>LVX>CIP |
| G+C | TGC>VAN>RIF, CXM>GAT>FDA>CAZ>MFX>OFX, GEN>TOB>LVX>CIP |
| G+B | VAN>GAT, RIF, CXM>FDA, LVX, CAZ, GEN, OFX, TOB>MFX, CIP (FDA>TOB) |
| G-C | CAZ>LVX, CIP, GEN, FDA |
| G-B | AMK>LVX, CAZ, RIF, CIP, OFX, GEN, GAT, TOB, VAN, CXM>FDA (LVX>CIP>CXM) |
Any sensitivity rate with a denominator number less than 15 was not included in this statistical analysis. TGC: Tigecycline; VAN: Vancomycin; RIF: Rifampicin; GAT: Gatifloxacin; CXM: Cefuroxime; FDA: Fusidic acid; CAZ: Ceftazidime; AMK: Amikacin; MFX: Moxifloxacin; OFX: Ofloxacin; GEN: Gentamicin; TOB: Tobramycin; LVX: Levofloxacin; CIP: Ciprofloxacin. “A>B, C” means the sensitivity of A was significantly higher than that of B and C (P<0.05), and no statistically significant difference was noted in the sensitivity of B and C (P>0.05).
DISCUSSION
Ocular infections are potentially blinding diseases[5], and bacteria are the most frequently encountered pathogens affecting ocular structures. Bacteria can cause many types of ocular infections such as conjunctivitis, keratitis, blepharitis, orbital cellulitis, dacryocystitis and endophthalmitis[6]. In this retrospective study, 3690 bacterial strains from a tertiary eye center over a period of 5y were analyzed. From January 2013 to December 2017, the positivity rate of bacterial culture in ocular specimens with suspected microbial infections was 31.44%, similar to the result reported by Beijing Tongren Hospital, one of the major eye centers in northern China (29.0%)[7]. Such similarity of findings may be partially explained by the reason that the two hospitals are both in northern China.
In the present study, G+C (82.30%) were prominent in the total bacterial isolates, and Staphylococcus accounted for the highest proportion (73.33%). S. epidermidis (54.39%) was the predominant bacterial isolate in the conjunctiva, cornea, aqueous humor or vitreous body, and other ocular sites, respectively. This finding is similar to those obtained in Britain[8], America[9], Australia[10], and Chinese minorities[11]. S. epidermidis was considered to be the most common bacterial isolate in the normal conjunctival sac[12]–[13] and one of the main pathogens of bacterial conjunctivitis[14]–[15]; it was also reported to be the main cause of bacterial keratitis[16]–[17] and postoperative endophthalmitis[18]–[19]. In this study, the predominant bacterial isolates were S. epidermidis (2007, 54.39%), S. aureus (260, 7.05%), C. xerosis (160, 4.34%), S. hominis (125, 3.39%), S. haemolyticus (115, 3.12%), and P. aeruginosa (77, 2.09%), which was different from a report in northern Ethiopia[20], where S. aureus (40, 21.5%), coagulase-negative staphylococci (31, 16.7%), P. aeruginosa (21, 11.3%), and E.coli (15, 8%) were the most common isolates. Differences in the regions and environment may be the reason of the discrepancy[21].
The use of effective broad-spectrum antibiotics for treatment of ocular bacterial infections before the availability of results of pathogen identification and antibiotic susceptibility tests is advocated in many studies[5],[22]. Empirical therapy relies on the susceptibility patterns of common bacteria isolated from eye specimens[23]. In the current study, the sensitivity rate of the total isolates to gatifloxacin was up to 90.01%, with G+C, G+B, G-C, and G-B being all highly sensitive to it, indicating that gatifloxacin is a broad-spectrum antibiotic with high sensitivity and is suitable for topical prophylactic use in ophthalmology. Levofloxacin has been the most frequently prescribed preoperative ophthalmic antibiotic for years, but our study showed that the sensitivity rate of the total isolates to it was low (51.91%), whereas that of G-B was high (83.66%). In an earlier study of 319 inpatients (319 eyes) diagnosed with infectious endophthalmitis at our institute[24], the sensitivity rates of bacteria to levofloxacin, tobramycin, gentamicin and ciprofloxacin were listed. Antibiotic sensitivities from two different studies at our institute are shown in Table 5. There was an obvious decline in the sensitivity of levofloxacin in the past few years. Meanwhile, Alabiad et al[25] argued that the resistance of fluoroquinolone including levofloxacin was common among all patient groups. According to the report by Huang et al[26] from our institution in 2009, G+C and G-B retained a high sensitivity to levofloxacin, but this current study showed that G+C were not as sensitive to levofloxacin (46.28%) as in the past (94.8%). Thus, levofloxacin may be no longer suitable for prophylactic use before eye surgery, but can be used to treat ocular infections caused by G-B.
Table 5. Antibiotic sensitivities form two different studies at our institute.
| Parameters | IES | OBIS |
| Study time | 2003-2010 | 2013-2017 |
| Gentamicin susceptible | 71.15 (74/104) | 66.59 (2455/3687) |
| Tobramycin susceptible | 77.22 (61/79) | 64.13 (2271/3541) |
| Levofloxacin susceptible | 81.82 (45/55) | 51.91 (1941/3739) |
| Ciprofloxacin susceptible | 69.52 (73/105) | 44.61 (1793/4019) |
IES: Infectious Endophthalmitis Study; OBIS: Ocular Bacterial Infections Study.
%
In previous reports, no resistance to vancomycin was identified among bacteria isolated from all types of ocular infections, and the sensitivity to this drug was confirmed[27]–[28]. In our study, however, the sensitivity rates of G+C and G+B to vancomycin were significantly higher than those of G-C and G-B (P<0.05), which is consistent with the results reported by Schimel et al[9] For fusidic acid, the sensitivity rate of gram-positive bacteria was high (88.91%), contrary to that of gram-negative bacteria (32.00%), with the rate of G+C being significantly higher than that of G-C and G-B, and the rate of G+B being significantly higher than that of G-B. Thus, fusidic acid is recommended to treat gram-positive bacterial infections.
The sensitivity rate of gram-negative bacteria to cefuroxime was as low as 59.25%, but it was only G-B whose sensitivity rate was 57.28%, while the sensitivity rate of G-C was 89.29%, significantly higher than that of G-B. For moxifloxacin, the sensitivity rate of gram-positive bacteria was as high as 80.28%, but it was only G+C whose sensitivity rate was 81.21%, while the sensitivity rate of G+B was just 32.00%, significantly lower than that of G+C. These findings remind us that further classifying bacteria and comparing the sensitivity rate by a statistical analysis would lead to more accurate results when analyzing antibiotic sensitivity. Tigecycline is a new type of active intravenous broad-spectrum antibiotic, which was reported to be used for treating bacterial keratitis resistant to current antimicrobials[29] and corneal neovascularization[30]. Tigecycline (99.59%), vancomycin (97.15%), and rifampicin (94.48%) exhibited a high efficacy on the total isolates, and the sensitivity of tigecycline was significantly higher than that of vancomycin in our study. By ranking the sensitivities of the different gram-stained isolates to the antibiotics (Table 4), we can select antibiotics with higher sensitivity rates to obtain better therapeutic effects when needed.
The findings of this study may help ophthalmologists make more appropriate decisions for the treatment of ocular bacterial infections. However, the retrospective nature of this study and limitation of research time, which determined our sample size, ultimately restricted our analyses on the variation trend of the pathogen distribution and antibiotic sensitivity. Further investigations on ocular bacterial infections with larger sample sizes, longer time, and more advanced techniques will be conducted in the future.
In conclusion, our 5-year study found that S. epidermidis was the main isolate of all ocular specimens with bacteria. As a broad-spectrum antibiotic with high sensitivity, gatifloxacin is more suitable than levofloxacin for topical prophylactic use in ophthalmology, and levofloxacin is an effective drug for treating G-B. Vancomycin and fusidic acid both have better effects on gram-positive bacteria than gram-negative bacteria. More accurate antibiotic sensitivity analysis results can be obtained by further classifying gram-stained bacteria and comparing their sensitivities through statistical analysis.
Acknowledgments
Foundations: Supported by the National Natural Science Foundation of China (No.81670839); the Shandong Medical and Health Science and Technology Development Program (No.2016WS0265); the Qingdao People's Livelihood Science and Technology Project (No.16-6-2-14-nsh).
Conflicts of Interest: Gao W, None; Xia T, None; Chen HB, None; Pan XJ, None; Huang YS, None; Wang X, None; Dong YL, None; Xie LX, None.
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