Distribution and Antibiotic Resistance Trends of Staphylococcus aureus : A 10-Year Retrospective Study

Abstract

Background and Objectives:

Staphylococcus aureus infection and its antibiotic resistance (ABR) situation are topical concerns. To formulate an effective response strategy tailored to our hospital and provide clinicians with a reliable basis for empirical antimicrobial use in the early phases of treatment.

Method:

Between 2014 and 2023, a total of 11,886 S. aureus isolates and 3,417 methicillin-resistant S. aureus (MRSA) isolates were enrolled. The distribution of these isolates over the 10-year period was analyzed, along with trends in ABR among all S. aureus isolates, those from respiratory tract specimens, those from pediatric patients, and MRSA isolates.

Results:

The detection number of S. aureus and MRSA strains showed an increasing trend over the 10-year period. However, while the proportion of S. aureus among Gram-positive strains (G+) remained stable, its proportion among all bacterial pathogens (BPS) decreased. S. aureus and MRSA strains were primarily isolated from respiratory tract specimens, wound pus, and blood specimens. The top three departments with the highest detection rates of S. aureus were Pediatrics, Pediatric Surgery, and Orthopedics, in order. Resistance rates to oxacillin and penicillin G were nearly universal, approaching 100%. In contrast, resistance to gentamicin, rifampicin, ciprofloxacin, levofloxacin, moxifloxacin, cotrimoxazole, clindamycin, erythromycin, and tetracycline showed different downward trends across the four study groups.

Conclusion:

In conclusion, the prevalence of S. aureus infections within our hospital remains a significant concern. It is imperative to closely monitor the epidemiological distribution and ABR patterns of this pathogen to facilitate early intervention and guide appropriate therapeutic strategies.

Keywords

MRSA antibiotic resistance distribution trend

Introduction

Antibacterial resistance is a serious global public health concern, accounting for 4.95 million deaths in 2019, primarily in low- and middle-income countries (LMIC). Infections with antibiotic resistance (ABR) pathogens cause a considerable worldwide illness burden. The World Health Organization (WHO) has issued the 2024 Bacterial Priority Pathogens List (BPPL), which builds on the 2017 BPPL and contains 15 ABR pathogen families classified as critical, high, and medium.¹ Methicillin-resistant Staphylococcus aureus (MRSA) remains in the BPPL high-priority pathogen category, consistent with its high estimated burden.²

S. aureus is regarded as one of the most common bacteria responsible for both community- and noncommunity-acquired infections, and it has been linked to high morbidity and mortality rates, rising from 103,000 attributable deaths in 1990 to 196,000 attributable deaths in 2021.³ Vigilant surveillance of antimicrobial resistance (AMR) trends is fundamental to global control efforts. It directly supports resistance containment by generating essential epidemiological data that guide prevention initiatives and optimize treatment protocols.^4,5

Serving as the regional medical center for northwestern Sichuan, our institution is uniquely positioned to contribute relevant data on AMR. This retrospective analysis provides a 10-year (2014–2023) epidemiological portrait of S. aureus infections in a general tertiary hospital, detailing prevalence, distribution, and temporal trends of ABR. Thus, this work aims to inform evidence-based clinical decision-making and antibiotic stewardship policies.

Materials and Methods

Source of strains

In our retrospective study, S. aureus strains were isolated from specimens collected from outpatients and inpatients who had enrolled in a general tertiary hospital in southwest China between January 2014 and December 2023. After duplicate strains were eliminated in accordance with the principle of keeping the first strain of the same germs in the same patient, a total of 11,886 S. aureus strains were identified. See Fig. 1 for the process diagram of this study.

FIG. 1.

Study flow diagram.

Bacterial identification and susceptibility testing

Upon collection, patient specimens were transported to the clinical microbiology laboratory. According to standard protocols, microorganisms were isolated and cultured. Subsequently, preliminary identification of the cultured isolates was performed by laboratory technologists to determine the necessity of further purification or definitive identification. The VITEK^®2 Compact automatic microbiological analyzer (BioMérieux, Marcy l’Etoile, France) was used to identify bacterial species and conduct antibiotic susceptibility tests. Since 2019, the VITEK-MS system (BioMérieux, Marcy l’Etoile, France) has also been applied to identify bacterial species. The antimicrobial susceptibility tests were interpreted in accordance with the Clinical and Laboratory Standards Institute’s (CLSI) criteria, and the intermediate was attributed as resistant in this study.

Statistical analysis

In this study, the ABR profiles were obtained by WHONET 5.6 software and reported as percentages. This study categorized S. aureus isolates into four distinct groups for longitudinal analysis of ABR trends. The objective was to delineate source- and type-specific ABR characteristics. The general group, representing the overall ABR profile and infection epidemiology within the whole hospital, served as the baseline control for intergroup comparisons. Given that the majority of S. aureus isolates were recovered from respiratory tract specimens, analyzing this subgroup provides critical insights into ABR patterns associated with respiratory tract infections. The pediatric group was examined separately to address the unique therapeutic challenges and stricter antibiotic requirements in children, thereby generating evidence to guide pediatric antimicrobial stewardship. Finally, given the significant increase in mortality associated with MRSA, dedicated analysis of its ABR trends is essential for developing effective strategies to combat resistant infections.

The statistical analysis of data was performed using SPSS 26.0 software (SPSS Inc., Chicago, USA). Means and standard deviations were determined for continuous variables with a normal distribution. Non-normally distributed continuous variables were measured using medians and interquartile ranges (IQR). The χ² test was used for comparison between groups. The Mann–Kendall test was used to compare proportions and trends across years, and the Z-value was utilized to examine the trend of drug resistance rates. A p value <0.05 was defined as statistically significant.

Results

This study analyzed the number and proportion of S. aureus strains isolated at our hospital over a 10-year period, from January 1, 2014, to December 31, 2023. A total of 11,886 S. aureus strains were enrolled, of which 7,108 (59.8%) were obtained from male patients and 4,778 (40.2%) from female patients. Based on clinical setting, 273 (2.3%) isolates were from outpatients and 11,613 (97.7%) from inpatients. Over the decade, the mean age of patients with S. aureus infection showed a V-shaped trend (Fig. 2), declining from 38.9 years in 2014 to a nadir of 30.4 years in 2016, before rising again to 44.6 years by 2023.

FIG. 2.

Mean age of patients infected with Staphylococcus aureus by year.

Strains changes by year

Figure 3 demonstrates that the total number of isolated bacterial pathogens (BPS), Gram-positive bacteria (G+), and S. aureus increased annually over the study period, with the exception of G + and S. aureus in 2020. In contrast, the proportions of both S. aureus/BPS and G+/BPS showed a downward tendency. S. aureus/BPS decreased from 11.1% in 2014 to 9.4% in 2023, while G+/BPS decreased from 24.7% to 20.1% over the same period. In comparison, S. aureus/G + remained relatively stable, fluctuating between 42.0% and 47.7%. The consistent upward trend in BPS indicates a growing clinical burden of bacterial infections.

FIG. 3.

The changes of strains by year.

Distribution of S. aureus by specimen type

Of 11,886 S. aureus strains, 51.7% were recovered from respiratory tract specimens, followed by wound pus (31.6%), blood (12.3%), and urine (5.6%) (Fig. 4A). Respiratory tract showed a fluctuating trend over time, rising from 44.8% in 2014 to 57.5% in 2017, then declining to 45.5% in 2022 before increasing again to 57.4% in 2023 (Fig. 4B). Wound pus isolates were lowest in 2016 (19.5%), and they lingered between 30% and 40% in subsequent years. Urine isolates remained consistently low. In contrast, the proportion of blood isolates exhibited an upward trend, increasing from 2.6% in 2014 to 8.2% in 2022, before decreasing to 2.9% in 2023.

FIG. 4.

Distribution of Staphylococcus aureus by specimen types. (A) The distribution of 11,886 S. aureus strains in various specimens. (B) Proportion of S. aureus in primary specimens, 2014–2023.

Distribution of S. aureus by departments

Between 2014 and 2023, the departments with the highest detection rates of S. aureus were as follows: pediatric department (3,492 strains, 29.4%), otolaryngology department (1,016 strains, 8.5%), intensive care unit (ICU; 919 strains, 7.7%), orthopedic department (768 strains, 6.5%), dermatology department (698 strains, 5.9%), burn and plastic surgery department (556 strains, 4.7%), pediatric surgery department (458 strains, 3.9%), neurosurgery department (443 strains, 3.7%), and pneumology department (353 strains, 3.0%). After 2019, the proportion of isolates from the pediatric department dropped below 30%, but rebounded to 30.0% by 2023. Notably, the highest proportion of S. aureus isolates in the ICU was observed between 2020 and 2022. In other departments, the prevalence of S. aureus exhibited wavelike fluctuations with no marked variation across the years, as illustrated in Fig. 5.

FIG. 5.

Distribution of Staphylococcus aureus by departments.

Distribution of MRSA

A total of 3,417 MRSA strains were isolated. Both the number and proportion of MRSA isolates increased annually, reaching a peak in 2023 (539 strains, 34.7%) (Fig. 6C). The distribution of MRSA across hospital departments was as follows: pediatric department (1,001 strains, 29.3%), ICU (295 strains, 8.6%), orthopedics department (256 strains, 7.5%), otolaryngology department (223 strains, 6.5%), burns and plastic surgery department (168 strains, 4.9%), dermatology department (163 strains, 4.8%), infectious diseases department (143 strains, 4.2%), neurosurgery department (113 strains, 3.3%), nephrology department (84 strains, 2.5%), and cerebral surgery department (81 strains, 2.4%) (Fig. 6B). The top six departments with the highest MRSA counts were the same as those with the most S. aureus isolates overall, although their relative rankings varied. Notably, the pediatric department ranked first in both lists. The majority of MRSA strains were isolated from respiratory tract specimens (1,787 strains, 52.3%), followed by wound pus (1,018 strains, 29.8%), blood (226 strains, 6.6%), stool (76 strains, 2.2%), and ear specimens (58 strains, 1.7%) (Fig. 6A). As urine specimens were not included in this analysis, these findings differ slightly from the primary sources reported for overall S. aureus.

FIG. 6.

Distribution of MRSA. (A) Distribution of 3,417 MRSA by specimens. (B) Distribution of 3,417 MRSA by departments. (C) Distribution of MRSA by year. MRSA, methicillin-resistant Staphylococcus aureus.

Antibiotic resistance of S. aureus by year

In this study, ABR trends in S. aureus were assessed from four different perspectives (Tables 1–4): overall S. aureus, respiratory tract specimens, pediatric department, and MRSA. Penicillin G resistance remained consistently high across all categories, with rates of 98.4%, 98.2%, 97.2%, and 100%, respectively.

Table 1.

Changing Resistance Rates of Staphylococcus aureus to 16 Antimicrobial Agents, 2014–2023

Antimicrobial agent	2014N = 661	2015N = 805	2016N = 1,124	2017N = 1,182	2018N = 1,243	2019N = 1,236	2020N = 1,220	2021N = 1,372	2022N = 1,490	2023N = 1,553	Z	p
Penicillin G	95.0	92.1	94.1	95.3	93.7	94.4	94.1	92.9	95.2	98.4	0.805	NS
Oxacillin	19.7	21	22.6	26.5	26.5	29.1	36.3	33.6	36.2	33.8	3.130	<0.01
Gentamicin	14.4	13.9	12.5	13	9.4	9.5	10.9	6.6	7.5	5.4	−3.041	<0.01
Rifampicin	2.1	2.4	1.3	2.1	1.8	2.4	3.0	0.7	0.5	0.6	−1.252	NS
Ciprofloxacin	13.0	12.6	11.7	15.0	13.2	12.7	13.6	14.3	14.1	12.7	0.805	NS
Levofloxacin	13.2	12.4	11.1	15.0	13.0	12.5	13	14.0	13.9	12.7	0.447	NS
Moxifloxacin	8.8	10.8	8.2	10.1	10.6	9.7	9.8	10.1	11.0	9.0	0.447	NS
Cotrimoxazole	23.0	21.5	19.0	19.1	16.7	15.6	16.0	14.9	15.6	14.6	−3.309	<0.01
Clindamycin	68.1	66.1	40.8	40.2	39.0	33.9	34.8	36.2	32.8	33.0	−3.220	<0.01
Erythromycin	70.7	67.8	68.5	67.9	64.7	65.9	60.7	64.4	60.8	59.4	−3.041	<0.01
Nitrofurantoin	0.2	0	0	0	0.1	0	0.1	0.1	0	0.2	0.537	NS
Linezolid	0	0	0	0	0	0	0	0	0	0	0	NS
Vancomycin	0	0	0	0	0	0	0	0	0	0	0	NS
Quinupristin/dalfopristin	27.2	26.1	0	0	0	0	0	0.1	0	0.1	−0.537	NS
Tetracycline	32.2	28.6	26.7	25.8	24.2	24.4	21.1	21.4	22.7	19.1	−3.220	<0.01
Tigecycline	0	0	0	0	0	0	0	0	0	0	0	NS

Mann–Kendall test t showed linear upward trends for resistance to oxacillin, while linear downward trends for resistance to gentamicin, cotrimoxazole, clindamycin, erythromycin, and tetracycline from 2014 to 2023.

Data are presented as % unless otherwise specified.

NS, not significant.

Table 2.

Changing Resistance Rates of Staphylococcus aureus to 16 Antimicrobial Agents in Respiratory Tract Specimen, 2014–2023

Antimicrobial agent	2014N = 296	2015N = 436	2016N = 634	2017N = 680	2018N = 686	2019N = 586	2020N = 606	2021N = 656	2022N = 678	2023N = 891	Z	p
Penicillin G	93.9	92.1	94.7	94.6	94.8	93.5	93.1	93.0	95.0	98.2	0.894	NS
Oxacillin	19.5	20.9	23.7	27.2	30.1	32.1	32.4	38.0	39.0	36.8	3.578	<0.01
Gentamicin	14.3	13.8	12.8	13.7	9.9	8.2	10.0	6.7	6.9	5.5	−3.220	<0.01
Rifampicin	2.0	2.2	1.2	0.7	1.5	1.6	2.5	0.7	0.2	0.3	−1.521	NS
Ciprofloxacin	12.8	12.5	12.3	14.0	11	12.3	15.4	14.7	16.1	11.9	0.447	NS
Levofloxacin	13.1	12.2	11.5	13.8	10.9	12.1	15.2	14.5	16.1	11.9	0.716	NS
Moxifloxacin	8.7	10.6	10.1	9.1	8.9	9.4	11.6	8.8	13.0	8.5	0	NS
Cotrimoxazole	22.7	21.3	17.7	21.1	17.5	14.0	14.0	14.1	15.5	15.0	−2.236	<0.05
Clindamycin	67.8	66.0	37.1	41.7	42.6	34.2	29.1	37.0	33.0	33.6	−2.504	<0.01
Erythromycin	70.8	67.7	66.7	67.8	65.9	62.3	51.4	63.2	59.9	57.3	−2.862	<0.01
Nitrofurantoin	0.2	0	0	0	0	0	0	0.2	0	0.3	0.537	NS
Linezolid	0	0	0	0	0	0	0	0	0	0	0	NS
Vancomycin	0	0	0	0.2	0	0	0	0	0	0	−0.179	NS
Quinupristin/dalfopristin	27.1	26.0	0	0	0	0	0	0.2	0	0	−1.163	NS
Tetracycline	32.3	28.5	27.2	26.1	23.2	25.7	22.0	21.9	23.1	18.2	−3.399	<0.01
Tigecycline	0	0	0	0	0	0	0	0	0	0	0	NS

Data are presented as % unless otherwise specified.

Table 3.

Changing Resistance Rates of Staphylococcus aureus to 16 Antimicrobial Agents in Pediatric Department, 2014–2023

Antimicrobial agent	2014N = 200	2015N = 268	2016N = 370	2017N = 409	2018N = 454	2019N = 333	2020N = 270	2021N = 379	2022N = 343	2023N = 466	Z	p
Penicillin G	93.8	92.2	94.7	94.8	94.1	94.0	90.7	91.4	93.8	97.2	0	NS
Oxacillin	19.5	19.9	24.2	30.2	31.5	32.8	34.1	35.5	39.6	35.4	3.578	<0.01
Gentamicin	8.8	9.0	7.8	7.9	6.8	8.7	5.9	8.3	1.8	3.9	−2.147	<0.01
Rifampicin	0.6	0.5	0.7	0.5	0	0	0	0.6	0.4	0	−1.431	NS
Ciprofloxacin	6.8	6.5	6.0	7.6	6.5	7.0	7.8	6.1	7.7	5.8	0	NS
Levofloxacin	7.1	6.8	6.0	7.6	6.5	6.7	7.3	6.1	7.7	5.6	−0.358	NS
Moxifloxacin	3.6	3.7	3.5	3.7	5.3	4.0	5.4	4.8	6.2	4.2	2.236	<0.05
Cotrimoxazole	17.1	16.5	16.1	14.3	18.1	11.9	12.7	13.7	11.0	11.7	−2.504	<0.01
Clindamycin	65.3	60.3	38.0	40.3	47.2	38.1	36.6	33.9	30.0	31.8	−3.041	<0.01
Erythromycin	72.2	70.4	69.6	66.8	71.5	66.6	64.9	59.7	56.0	59.6	−3.220	<0.01
Nitrofurantoin	0.1	0	0	0	0	0	0	0	0	0	−0.718	NS
Linezolid	0	0	0	0	0	0	0	0	0	0	0	NS
Vancomycin	0	0	0	0	0	0	0	0	0	0	0	NS
Quinupristin/dalfopristin	25.2	23.5	0	0	0	0	0	0.3	0	0	−1.163	NS
Tetracycline	28.6	25.9	21.0	22.4	18.1	22.1	24.4	18.8	20.5	15.0	−2.147	<0.05
Tigecycline	0	0	0	0	0	0	0	0	0	0	0	NS

Mann–Kendall test t showed linear upward trends for resistance to oxacillin and moxifloxacin, while linear downward trends for resistance to gentamicin, cotrimoxazole, clindamycin, erythromycin, and tetracycline from 2014 to 2023.

Data are presented as % unless otherwise specified.

Table 4.

Changing Resistance Rates of MRSA to 16 Antimicrobial Agents, 2014–2023

Antimicrobial agent	2014N = 184	2015N = 219	2016N = 262	2017N = 325	2018N = 357	2019N = 369	2020N = 364	2021N = 385	2022N = 413	2023N = 539	Z	p
Penicillin G	100	100	100	100	100	100	100	100	100	100	0	NS
Oxacillin	100	100	100	100	100	100	100	100	100	100	0	NS
Gentamicin	21.1	19.5	13.4	11.7	12.3	8.6	13.5	3.9	6.5	4.9	−2.683	<0.01
Rifampicin	8.5	9.3	9.1	8.3	8.0	7.0	7.7	2.0	0.6	1.2	−3.220	<0.01
Ciprofloxacin	20.3	19.4	18.9	17.5	18.1	13.6	20.3	12.0	18.6	15.9	−1.700	<0.05
Levofloxacin	19.5	18.7	19.3	20.4	16.5	13.3	19.0	10.9	18.2	16.3	−1.789	<0.05
Moxifloxacin	13.4	13.8	14.9	15.6	13.7	11.1	14.7	8.0	15.6	10.9	−0.447	NS
Cotrimoxazole	8.3	8.6	10.8	11.5	9.1	6.5	15.6	9.2	16.7	11.3	1.610	NS
Clindamycin	79.8	77.5	74.3	71.6	70.2	68.1	63.7	69.3	60.2	59.8	−3.578	<0.01
Erythromycin	89.5	87.6	88.4	85.7	83.9	84.2	72.0	80.9	82.2	72.0	−2.952	<0.01
Nitrofurantoin	0.6	0	0.5	0	0.1	0	0.2	0.2	0	0.6	0.089	NS
Linezolid	0	0	0	0	0	0	0	0	0	0	0	NS
Vancomycin	0	0	0	0	0	0	0	0	0	0	0	NS
Quinupristin/dalfopristin	40.8	38.8	0.2	0.2	0	0	0	0.2	0	0.2	−1.610	NS
Tetracycline	42.5	41.6	40.7	40.5	41.0	40.3	32.3	29.3	29.9	27.8	−3.399	<0.01
Tigecycline	0	0	0	0	0	0	0	0	0	0	0	NS

Mann–Kendall test t showed linear downward trends for resistance to gentamicin, rifampicin, ciprofloxacin, levofloxacin, clindamycin, erythromycin, and tetracycline from 2014 to 2023.

Data are presented as % unless otherwise specified.

MRSA, methicillin-resistant Staphylococcus aureus.

Table 1 shows the trend in overall S. aureus resistance from 2014 to 2023. Oxacillin resistance increased steadily from 19.7% in 2014 to 33.8% in 2023 (Z = 3.130, p < 0.01). In contrast, resistance to gentamicin, cotrimoxazole, clindamycin, erythromycin, and tetracycline decreased significantly, from 14.4% to 5.4% (Z = −3.041, p < 0.01), 23% to 14.6% (Z = −3.309, p < 0.01), 68.1% to 33.0% (Z = −3.220, p < 0.01), 70.7% to 59.4% (Z = −3.041, p < 0.01), and 32.2% to 19.1% (Z = −3.041, p < 0.01), respectively. Rifampicin resistance declined from 2.1% in 2014 to 0.6% in 2023, peaking transiently at 3% in 2020. Quinupristin/dalfopristin resistance exhibited the most pronounced decline from 27.2% in 2014 and 26.1% in 2015 to near absence after 2016. Ciprofloxacin resistance maintained between 11.7% and 15.0%, while levofloxacin and moxifloxacin resistance rates ranged from 11.1% to 15.0% and 8.8% to 11.0%, respectively. No resistance to linezolid, vancomycin, and tigecycline was detected throughout the study period, affirming their utility as last-resort treatments for S. aureus infection. Regretfully, intermittent nitrofurantoin-resistant strains were detected in 2014, 2018, 2020, 2021, and 2023.

Overall, the ABR profiles and trends observed in the respiratory tract specimens were comparable with those of the general S. aureus population, with no discernible differences (Table 2).

Table 3 presents the resistance rates among pediatric isolates. The prevalence of oxacillin resistance increased from 19.5% in 2014 to 35.4% in 2023 (Z = 3.578, p < 0.01), whereas moxifloxacin resistance fluctuated between 3.5% and 7.7% (Z = 2.236, p < 0.05), with both exhibiting overall upward trends. Resistance to gentamicin (Z = −2.147, p < 0.05), cotrimoxazole (Z = −2.504, p < 0.01), clindamycin (Z = −3.041, p < 0.01), erythromycin (Z = −3.220, p < 0.01), and tetracycline (Z = −2.147, p < 0.01) was slightly lower in the pediatric department compared with the general group and demonstrated a declining trend. Notably, gentamicin resistance remained around 8% until 2021, then decreased sharply to 1.8% in 2022 and 3.9% in 2023. Rifampicin resistance consistently remained below 1%, and levofloxacin resistance stabilized at approximately 6.5%. Cotrimoxazole resistance ranged from 14.3% to 18.1% between 2014 and 2018 and remained around 11% after 2019. Clindamycin resistance decreased markedly from 65.3% in 2014 to 31.8% in 2023. However, erythromycin consistently remained a high resistance over 56.0%. Tetracycline resistance rate showed a fluctuating downward trend. No resistance to linezolid, vancomycin, and tigecycline was detected.

Table 4 summarizes the ABR profiles of MRSA strains. Compared with overall S. aureus, the MRSA group exhibited generally higher resistance rates to the antibiotics, with the exception of cotrimoxazole. Significantly declining trends in resistance were observed for gentamicin (Z = −2.683, p < 0.01), clindamycin (Z = −3.578, p < 0.01), erythromycin (Z = −2.952, p < 0.01), tetracycline (Z = −3.399, p < 0.01), and rifampicin (Z = −3.220, p < 0.01), as well as for ciprofloxacin (Z = −1.700, p < 0.05) and levofloxacin (Z = −1.789, p < 0.05). Notably, no resistance to linezolid, vancomycin, or tigecycline was detected among the MRSA isolates.

Discussion

Demographics

Since 2016, the average age of patients with S. aureus infection has consistently increased, yet remains below 45 years. A significant male predominance (59.8% vs. female 40.2%) was observed. These findings indicate that younger adults constitute a key affected population in this region. Unlike studies focusing on specific disease-related manifestations such as S. aureus bacteremia (SAB), this study collected data from all individuals diagnosed with S. aureus infection over a 10-year period. This demographic pattern diverges from reports in other settings. For instance, the average age of S. aureus-infected patients in Denmark was 64 years, with incidence rising with age.⁶ Similarly, aggregated data from 29 European countries indicated a mean age exceeding 60 years,⁷ while other investigations have been confined to pediatric populations.⁸ As age is a recognized factor influencing MRSA epidemiology, its consideration is crucial for shaping effective preventive strategies against resistant infections.⁹ Regarding sex disparities, a modest correlation with bacterial resistance has been confirmed.⁷ Although incidence is lower in women and their clinical management may differ, mortality risk following SAB is comparable between sexes.¹⁰ Therefore, further elucidating the role of sex in S. aureus infection—including incidence, infection site, resistance patterns, outcome, and prognosis—represents an important direction for future research.

According to CHINET 2023 data,¹¹ S. aureus accounted for 9.2% of BPS in 2023, ranking third among all pathogens. From 2005 to 2023, G+/BPS ranged from 27.0% to 34.3%. In the present study, S. aureus/BPS exceeded 9.2% in all years except 2020 (9.0%) and 2021 (8.7%), which is higher than the 6.6% reported by Chang et al. for 2021.¹² Additionally, this study calculated the ratio of S. aureus/G+, which remained above 42.0% throughout the study period—significantly exceeding the 18.7% reported by Chang et al. for 2021.¹² Encouragingly, our investigation indicates a gradual decline in the S. aureus/BPS ratio, from 11.1% in 2014 to 9.4% in 2023. However, given the clinical significance of S. aureus infections in hospitals, ongoing annual surveillance of S. aureus/BPS and S. aureus/G+ ratios, along with timely intervention strategies in response to epidemiological shifts, remains essential.

Specimen trends

The distribution of S. aureus varies by specimen type, departments, and hospital. In this study, S. aureus was primarily isolated from respiratory tract specimens, wound pus, blood, and urine specimens. Its distribution and sequencing across departments were generally consistent with previous studies.¹³ In general, S. aureus was most frequently detected in respiratory tract specimens and was most commonly associated with the pediatric department, indicating that it has emerged as the primary pathogen of pediatric respiratory tract infection in our hospital. This finding aligns with other published studies. For instance, researchers in Wuxi City also reported S. aureus as the most common pathogen in sputum cultures from children, with prevalence rates of 27.21% in children aged 1 month to 3 years and 25.81% in those aged 3–6 years.¹⁴

According to our research, the rate of S. aureus in respiratory tract specimens remained below 50% between 2020 and 2022 but increased markedly to 57.4% in 2023. This surge may be attributed to public health measures implemented during the COVID-19 pandemic. The second most common source of S. aureus isolates was wound pus. Appropriate wound care and medication can effectively prevent nosocomial S. aureus infections.¹⁵ SAB is a common condition associated with high morbidity and mortality. Surprisingly, SAB was associated with 30-day mortality only when the time to positive culture exceeded 24 hours,¹⁶ and coinfection with other pathogens may lead to more severe outcomes.¹⁷ Despite novel rapid diagnostic methods for SAB have been developed,^18,19 blood culture remains the gold standard in our hospital. Therefore, efforts should focus on improving the positivity rate of blood culture while shortening the time to positivity.

MRSA burden

The emergence and spread of MRSA are associated with increased mortality and prolonged hospitalization.²⁰ However, the burden of MRSA exhibits considerable geographic disparities due to factors such as transmission, genetic diversity, evolution, and differences in local surveillance and treatment practices. In the present study, MRSA rates remained below 30% until 2022, lower than the national level of 30.5%²¹; however, in 2023, the MRSA rate rose to 34.7%, exceeding the national level of 29.6%.¹¹ Further research is needed to ascertain the cause of this notable increase. The pediatric department demonstrated the highest MRSA detection rate of 29.3%, which was slightly lower than the national rate of 31.2%.²² This may be attributable to strict adherence to pediatric antibiotic stewardship guidelines at our institution. Additionally, the MRSA detection rate in stool specimens was 2%, lower than the fecal carriage rate of 4.5% among pediatric patients in Guangzhou.⁸ Nevertheless, ongoing surveillance remains essential. Effective management of MRSA infections requires prompt identification of infection sites, culture and susceptibility testing, evidence-based treatment, and appropriate infection control measures.

Antibiotic resistance patterns

The prevalence and trends of ABR in S. aureus vary by region, underscoring the necessity of continuous surveillance to guide the rational use of antibiotics in clinical practice.²³ This study reveals that although resistance rates vary among the four groups examined, the overall pattern remains consistent. With the exception of cotrimoxazole, MRSA strains demonstrated higher resistance rates to the same antibiotics compared with the other three groups within the same year. The pediatric group showed the lowest resistance rate, while no significant difference was observed between the respiratory tract specimen group and the general S. aureus group. Our findings indicate that the resistance rate of S. aureus to oxacillin increased annually but remained <40%, in contrast to a previously reported rate exceeding 80% in 2018.²⁴ Moreover, unlike domestic reports, resistance to gentamicin, clindamycin, erythromycin, and tetracycline across the four groups showed a declining trend over time.^24–27

Upon retrospective analysis, the early warning system for rational drug use implemented in 2019, coupled with a hierarchical management strategy for clinical antimicrobials (e.g., reclassifying ciprofloxacin from “unrestricted” to “restricted”), has yielded substantial benefits. Additionally, in compliance with the “Administrative Measures for the Clinical Application of Antibiotics,” mandatory regular training on antimicrobial stewardship has been enforced for physicians and pharmacists since 2021, with corresponding prescribing and dispensing privileges contingent upon successful completion of standardized assessments. These interventions have collectively contributed to a reduction in ABR rates observed at our hospital. Concurrently, strategies such as combination antibiotic therapy and the adoption of novel agents have been employed to counter the spread of resistance.^28,29

Conclusions

S. aureus isolates were primarily from the pediatric department and respiratory tract specimens. The annual increase in both total S. aureus isolates and MRSA incidence highlights the need for identifying root causes and implementing solutions. Except for cotrimoxazole, resistance rates to the same drug descended in the order of: MRSA group, general S. aureus group, respiratory tract group, and pediatric department group. Resistance to gentamicin, rifampicin, ciprofloxacin, levofloxacin, clindamycin, erythromycin, and tetracycline declined yearly. A vancomycin-resistant strain was detected in a respiratory tract specimen in 2017, but no linezolid- or tigecycline-resistant strains have been isolated.

In conclusion, the S. aureus infection status in our hospital remains an ongoing challenge. Continuous surveillance of the distribution and resistance trends of S. aureus is essential to guide early intervention and optimize infection treatment.

Authors’ Contributions

Y.L.: Collected and assembled the data. M.Z.: Was responsible for data analysis. Y.W.: Drafted the original article; all the authors endorsed the final article.

Footnotes

Ethics Approval and Consent to Participate

The study was approved by the Ethics Committee Office, Mianyang Central Hospital, Mianyang City, Sichuan Province, China (No. 2S202403146-01). The requirement for informed consent was waived due to the study’s retrospective nature.

Consent for Publication

All authors have agreed to the submitted version of the article.

Availability of Data and Materials

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Disclosure Statement

No competing financial interests exist.

Funding Information

This research received no external funding.

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