Impact of the 13-valent pneumococcal vaccine on Streptococcus pneumoniae serotypes and antibiotic susceptibility in children

Abstract

Objective

To examine the impact of the 13-valent pneumococcal vaccine on Streptococcus pneumoniae serotypes and antibiotic susceptibility in children to inform the prevention and treatment of S. pneumoniae infections.

Methods

We analyzed and compared S. pneumoniae serotypes and antibiotic susceptibility between children vaccinated with 13-valent pneumococcal vaccine (vaccinated group) and unvaccinated children (control group).

Results

We collected 167 S. pneumoniae strains that met the study requirements from 60 children (35.92%) in the vaccinated group and 107 (64.08%) children in the control group. The antibiotic susceptibility test revealed no significant difference in susceptibility to oral penicillin (a β-lactam) or penicillin injection between the two groups. Of the third-generation cephalosporins, susceptibility to ceftriaxone and cefotaxime differed significantly among children with meningitis between the two groups (P < 0.05) but not among children without meningitis. In total, 167 strains were susceptible to vancomycin. Neither of the groups were susceptible to erythromycin.

Conclusions

The majority of the S. pneumoniae serotypes isolated from children in Xiamen were covered by the 13-valent pneumococcal vaccine. The isolated S. pneumoniae strains were highly resistant to erythromycin and tetracycline but remained susceptible to vancomycin. Children vaccinated with the 13-valent pneumococcal vaccine may benefit from parenteral third-generation cephalosporins after developing pneumococcal meningitis.

Keywords

Pneumococcal diseases vaccination antibiotic susceptibility testing

Introduction

Streptococcus pneumoniae is a common pathogen that causes infectious diseases in children. Clinical infections caused by S. pneumoniae are collectively known as pneumococcal diseases (PDs). In developing countries, PDs are a leading cause of death and disability in children aged <5 years.¹ In China, S. pneumoniae infections among children aged <5 years account for 12% of total global cases, ranking second in prevalence worldwide.² S. pneumoniae can infect the upper respiratory tract and cause sinusitis and tonsillitis. It also infects other body sites and causes several invasive PDs, such as pneumonia, meningitis, and sepsis. Domestic and foreign studies have confirmed that inoculation of a pneumococcal conjugate vaccine can not only reduce the morbidity and mortality of S. pneumoniae infections but also decrease antibiotic resistance. In 2017, the 13-valent pneumococcal vaccine (PCV13) was introduced in Xiamen. This study focused on the impact of PCV13 on S. pneumoniae serotype distribution in Xiamen and analyzed the S. pneumoniae serotypes and antibiotic susceptibility in children to provide insights into the prevention and treatment of this disease.

Materials and methods

Participants

We selected children hospitalized at Xiamen Children’s Hospital from whom S. pneumoniae was successfully isolated from their sputum, blood, cerebrospinal fluid, alveolar lavage fluid, or pus samples; serotyped; and tested for antibiotic susceptibility between September 2020 and March 2021. We de-identified all patient details. The inclusion criteria were as follows: (a) samples qualified without contamination; (b) strains successfully isolated, serotyped, and tested for antibiotic susceptibility; (c) children with complete data; (d) children vaccinated with PCV13; and (e) those whose parents signed the informed consent form for inclusion in the study. The study was approved by the Ethics Committee of the Institute of Xiamen Children’s Hospital ([2022] No. 38). The studies pooled for these analyses were performed according to the principles of the Declaration of Helsinki. As this study was a retrospective analysis, the need for informed consent from the patient and their family was exempted. Our study followed the relevant EQUATOR guidelines.³

Strain isolation, serotyping, and antibiotic susceptibility testing

Culture sputum, blood, cerebrospinal fluid, and other body fluid samples were collected from certain inpatients at the Xiamen Children’s Hospital between 2020 and 2021. The samples were plated onto Columbia blood agar plates containing 5% sheep blood and cultured at 35°C for 24–48 h under 5%–10% CO₂. The cultured bacterial strains were identified via morphological examination and optochin susceptibility test and were subsequently isolated. The bacterial strains were serotyped using polymerase chain reaction. Based on the gene sequences of each S. pneumoniae serotype in the gene database, serotype/group-specific primers were designed using the relevant primer software. According to the specific binding of the primer of a certain serotype to the DNA of the sample, a small fragment of a certain length was amplified, and the corresponding serotype was determined according to the size of the specific band after electrophoresis. The reagent kit was purchased from Shanghai Zhijiang Biotechnology Co., LTD. We performed antibiotic susceptibility testing using the VITEK 2 AST-GP68 Test Kit and interpreted the results based on the 2010 Clinical and Laboratory Standards Institute antimicrobial susceptibility testing standards.⁴

Statistical analysis

Data were statistically analyzed using IBM SPSS Statistics for Windows (version 26.0; IBM Corp., Armonk, NY, USA). Count data were expressed as percentage (%), and continuous data with normal distribution were expressed as mean ± standard deviation ( $\bar{x} \pm s$ ). Data were compared between the vaccinated and control groups using the chi-squared test, and a P-value of <0.05 was considered to indicate statistical significance.

Results

A total of 167 S. pneumoniae strains that met the study requirements were collected from 167 children, comprising 90 males (53.89%) and 77 females (46.11%), with a male-to-female ratio of 1:1.17. The mean participant age was 29.05 ± 16.64 (2.00–73.00) months. We assigned 60 children (35.92%) to the vaccinated group and 107 (64.08%) to the control group. No significant differences were observed in sex (P = 0.161) and age (P = 0.631) between the two groups (Table 1).

Table 1.

General patient characteristics and serotype distribution of 167 Streptococcus pneumoniae strains (n, %).

Parameter	Name	Group		P
Parameter	Name	Control group	Vaccinated group	P
Age		28.59 ± 16.55	29.88 ± 16.91	0.631
Sex
	Male	62 (57.94)	28 (46.67)	0.161
	Female	45 (42.06)	32 (53.33)	0.161
Serotype
	19F	43 (40.19)	26 (43.33)	0.692
	6B	19 (17.76)	10 (16.67)	0.858
	23A	10 (9.35)	1 (1.67)	0.055
	14	9 (8.41)	1 (1.67)	0.078
	19A	4 (3.74)	4 (6.67)	0.395
	23F	3 (2.80)	5 (8.33)	0.137
	3	6 (5.61)	2 (3.33)	0.713

The 167 strains were isolated from blood (5, 2.99%), alveolar lavage fluid (2, 1.20%), cerebrospinal fluid (1, 0.60%), pus (2, 1.20%), and predominantly sputum (157, 94.01%) samples.

The 167 S. pneumoniae strains identified in this study belonged to 14 serotypes, with serotype 19F being most common, followed by 6B, 23A, 14, 19A, 23F, 3, 15A, 6A, 15B, 11A, 10B, 34, and 7C. Of these, 143 strains were of serotypes 19F, 6B, 23A, 14, 19A, 23F, and 3, accounting for 85.63% of all strains identified. The dominant serotypes were not significantly different between the two groups (Table 1).

Antibiotic susceptibility test

β-lactams

1. Penicillin. Only 12.57% of the strains isolated from children with meningitis were susceptible to oral penicillin or penicillin injection, demonstrating high penicillin resistance. In contrast, 70.66% of the strains isolated from children without meningitis were susceptible to penicillin injection. 2. Third-generation cephalosporins. S. pneumoniae strains isolated from children without meningitis were generally susceptible to cefotaxime (97.60%) and ceftriaxone (97.01%). However, those from children with meningitis exhibited reduced susceptibility to the two antibiotics (31.74% and 37.93%, respectively).

Macrolides

The erythromycin resistance rate was 100%.

Carbapenems

The isolated S. pneumoniae strains were highly susceptible to meropenem (98.20%) and ertapenem (98.80%).

Quinolones

The test results showed that 97.62%, 99.40%, and 100% of the isolated strains were susceptible to ofloxacin, levofloxacin, and moxifloxacin, respectively.

Vancomycin

All 167 S. pneumoniae strains were susceptible to vancomycin (100%).

Tetracycline

The resistance rate was 93.41%.

Comparison of drug susceptibility test results

β-lactams

Resistance to cefotaxime and ceftriaxone was lower among children with pneumococcal meningitis in the vaccinated group than among those in the control group (P < 0.05). However, it was similar among children without pneumococcal meningitis in both groups. In contrast, resistance to penicillin did not differ significantly between the two groups regardless of the presence of meningitis (Table 2).

Table 2.

Antibiotic susceptibility test results (n, %).

Antibiotic	Control group (n = 107, 64.08%)		Vaccinated group (n = 60, 35.92%)		P
Antibiotic	Susceptible	Resistant/Intermediate	Susceptible	Resistant/Intermediate	P
Oral penicillin	12 (11.21)	95 (88.76)	9 (15.00)	51 (85.00)	0.479
Penicillin injection
Meningitis	13 (12.15)	94 (87.85)	8 (13.33)	52 (86.67)	0.825
Non-meningitis	72 (67.29)	35 (32.71)	46 (76.67)	14 (23.33)	0.202
Cefotaxime
Meningitis	28 (26.17)	79 (73.83)	25 (41.67)	35 (58.33)	0.039
Non-meningitis	103 (96.26)	4 (3.74)	60 (100.00)	0 (0.00)	0.298
Ceftriaxone
Meningitis	27 (25.33)	80 (74.77)	44 (73.33)	16 (26.67)	0.047
Non-meningitis	102 (95.33)	5 (4.67)	60 (100.00)	0 (0.00)	0.161
Vancomycin	107 (100.00)	0 (0.00)	60 (100.00)	0 (0.00)	1
Ofloxacin	106 (99.07)	1 (0.93)	57 (95.00)	3 (5.00)	0.133
Levofloxacin	107 (100.00)	0 (0.00)	59 (100.00)	1 (0.00)	0.359
Moxifloxacin	107 (100.00)	0 (0.00)	60 (100.00)	0 (0.00)	1
Ertapenem	105 (98.13)	2 (1.87)	60 (100.00)	0 (0.00)	0.537
Meropenem	104 (97.20)	3 (2.80)	60 (100.00)	0 (0.00)	0.554
Tetracycline	6 (5.61)	101 (94.39)	5 (8.33)	55 (91.67)	0.527
Chloramphenicol	98 (91.59)	9 (8.41)	52 (86.67)	8 (13.33)	0.313
Trimethoprim/sulfamethoxazole	19 (17.76)	88 (82.24)	9 (15.00)	51 (85.00)	0.647
Erythromycin	0 (0.00)	107 (100.00)	0 (0.00)	60 (100.00)	1
Telithromycin	106 (99.07)	1 (0.93)	58 (96.67)	2 (3.33)	0.293

Other antibiotics

Susceptibility to carbapenems, quinolones, erythromycin, and tetracycline remained unchanged (P > 0.05) in children who developed S. pneumoniae infections after PCV13 vaccination.

Discussion

Vaccination with PCV13 had no significant impact on serotype distribution in Xiamen during the same period; however, it may increase the number of nonvaccine serotypes (NVTs). More than 100 S. pneumoniae serotypes have been reported to date.⁵ Men et al.⁶ found that the serotypes 19A, 19F, 14, 23F, and 6B were the dominant S. pneumoniae serotypes causing childhood infections in mainland China. Our study demonstrated that 19A, 6B, 3, 14, and 23F were the major serotypes causing infections in Xiamen between 2020 and 2021. Consistent with the findings reported by Lin et al.,⁷ our subgroup analysis showed no significant changes in serotypes among children with S. pneumoniae infection in the same region during the same period.

In addition, we noted an increase in the number of NVTs such as 15A and 15B. Du et al.⁸ reported that the introduction of PCV13 in China increased the number of S. pneumoniae infections caused by the NVTs 15A and 15B. This increase in NVTs was likely attributed to serotype substitution resulting from vaccination-induced selective pressure^9,10 or serotype diversification¹¹ driven by bacterial capsule switching.⁸

The prevalence of drug resistance in S. pneumoniae is of particular concern, necessitating the rational selection of antibiotics based on the site of infection. Co-vaccination with PCV13 may increase antibiotic resistance.

β-lactams are widely used in the clinical treatment of S. pneumoniae infections in children. Penicillin is a commonly used β-lactam, and its resistance rate has steadily increased in Asian countries.¹² The present study also found an 87.43% resistance rate to oral penicillin and only 12.57% susceptibility to penicillin injection among children with pneumococcal meningitis. This was higher than the 76.4% penicillin resistance rate in Xiamen reported by Huang et al.¹³ in 2015. Furthermore, we found that up to 70.66% of S. pneumoniae strains were susceptible to penicillin injection in children without meningitis. This rate was lower than that reported by Fang et al.¹⁴ in 2018; however, it suggests that penicillin can still be the preferred treatment for patients without meningitis. Cephalosporins, especially third-generation cephalosporins, are β-lactams widely used to treat S. pneumoniae infections due to their excellent blood–brain barrier permeability. Our data revealed that the S. pneumoniae strains isolated from children without meningitis were highly susceptible to cefotaxime and ceftriaxone. In contrast, those isolated from children with meningitis were less susceptible to the two antibiotics (31.74% and 37.93%, respectively). However, the cephalosporin resistance rate was lower in the vaccinated group than in the control group, demonstrating that vaccination may counteract the enhancement of bacterial resistance to a certain extent, which aligns with the findings reported by Obolski et al.¹⁵

In agreement with a previous study,¹² our results showed that all strains were resistant to erythromycin (100%). Therefore, the clinical use of erythromycin should be avoided. Our study confirmed that S. pneumoniae remains highly susceptible to vancomycin, chloramphenicol, and quinolones. However, as these antibiotics are not clinically recommended for use in children, vancomycin combined with cefotaxime or ceftriaxone¹⁶ may be empirically administered before obtaining antibiotic susceptibility results. If susceptibility to β-lactams is confirmed, vancomycin should be discontinued.²

There are some limitations in this study. First, as a single-center retrospective analysis, only cases from Xiamen Children’s Hospital were included. This small sample size may not fully reflect all characteristics of PCV13 against the S. pneumoniae strain in children. Second, the cases originated in Xiamen, Fujian Province, China. Hence, population genetics and prevalent strains may differ from those in the remaining parts of China, which can lead to bias.

As the main pneumococcal vaccine used in Xiamen, PCV13 covered 79.88% of the strains identified in this study, which is consistent with previous findings.² Studies have demonstrated that the titers of immunoglobin G targeting the 13 vaccine serotypes were ≥0.35 µg/mL in >94.7% of children at 1 month after receiving the primary PCV13 immunization and in ≥98.6% of children following the booster dose at 12 months.¹⁷ Furthermore, these protective antibodies persisted for over 2 years.² Therefore, vaccination still plays a crucial role in preventing PD in children.

Footnotes

Acknowledgements

The authors thank the principal investigators, research practitioners, and patients involved in the study.

Author contributions

All authors greatly contributed to the research and preparation of this manuscript. SXZ, LY, YZ, and QL conceived the study and designed the experiments. LC, YZ, and HYL facilitated data collection, and all authors reviewed and approved the final version of the manuscript.

Consent for publication

Not applicable.

Data availability statement

The datasets generated and analyzed during the current study are not publicly available but are available from the corresponding author on reasonable request.

Declaration of conflicting interests

The authors declare that they have no competing interests.

Ethical considerations

The study was approved by the Ethics Committee of the Institute of Xiamen Children’s Hospital. The studies pooled for these analyses were all performed according to the principles of the Declaration of Helsinki.

Funding

This work was supported by the Health Guidance Project of Xiamen Science and Technology Bureau (Xiamen Medical and Health Guidance Project; No3502Z20209216).

ORCID iDs

Yuan Lin

Lou Qing

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