Pediatric Ear Culture Antibiogram for British Columbia Communities: A Retrospective Analysis of Outpatient Data (2020–2024)

Abstract

Background: Localized susceptibility data supports development of a pediatric-specific antibiogram to guide empiric therapy for ear infections within the British Columbia community setting. The aim of the current student was to construct an antibiogram from community-collected ear culture isolates to support antibiotic selection for ear infections in communities. Methods: Data were collected from patients <18 years of age with specimens submitted to LifeLabs British Columbia between 2020 and 2024, which included 2338 ear specimens. Organisms with ≥30 isolates undergoing antimicrobial susceptibility testing were included for analysis. Results: The most frequently identified organisms included methicillin-susceptible and methicillin-resistant Staphylococcus aureus (MSSA and MRSA, n = 648 and 80, respectively), Group A Streptococcus (GAS, n = 357), Pseudomonas aeruginosa (n = 316), Streptococcus pneumoniae (n = 105), and Haemophilus influenzae (n = 75). Beta-lactam antibiotics maintained high activity (>90%) against MSSA, GAS, and S. pneumoniae, while clindamycin and erythromycin showed significantly lower sensitivity against both MSSA (84% and 82%, respectively) and MRSA (79% and 50%, respectively) (p < 0.001). Trimethoprim–sulfamethoxazole and tetracycline demonstrated 99% and 97% susceptibility for MSSA, respectively, and 94% and 85% for MRSA, respectively. Conclusions: Beta-lactam antibiotics remain suitable for treatment against the pathogens S. pneumoniae, GAS, and MSSA, while trimethoprim–sulfamethoxazole is more suitable for MRSA.

1. Introduction

Acute otitis media is one of the most common infections in young children, characterized by swelling and infection of the middle ear space. It is estimated that approximately 80% of children will experience at least one episode by school age [1]. Otitis externa, an infection of external auditory canal, is also frequently encountered in children, presenting with similar signs [2]. Children with ear infections are at risk of complications, such as hearing impairment contributing to delayed speech development. Subsequently, there may be long-term implications for learning and childhood development. In more severe cases of otitis media, infections can lead to detrimental effects on the intratemporal and intracranial areas, adding to the importance of timely and appropriate therapy [3].

Despite the clinical significance of these infections, there is a lack of pediatric and community-based antibiogram data. Clinicians may rely on historical patterns or adult data when selecting antibiotics, which may not reflect current susceptibility trends in children. Although hospitals have developed antibiograms for ear infections, acute otitis media and otitis externa are often community-acquired infections [4,5,6]. Recognizing the need for targeted antibiotic prescribing, the Canadian Pediatric Society has advocated for age-specific antibiograms constructed by regional laboratories for use by clinicians to support evidence-based prescribing in selected infections [7]. Although the Canadian Pediatric Society has a position statement on management of ear infections in children, it is unknown whether its guidance is applicable to every community in Canada [8].

Making a community-based antibiogram does come with challenges, such as lack of a centralized laboratory to take on the responsibility and unique testing criteria and small sample size in each outsourced laboratory [9]. LifeLabs British Columbia (BC) is in a good position to undertake this task given its broad coverage of community regions in the province, including 129 patient service centers for specimen collection. The aim of the current study was to construct a novel enhanced antibiogram from community-collected ear culture isolates to support antibiotic selection for ear infections in the community.

2. Materials and Methods

2.1. Data Collection and Analysis

The current retrospective audit was conducted using Microbiology Electronic Worksheet System (MEWS; Version 5.00.267; LifeLabs, Toronto, ON, Canada), a software application that generated data of all reported ear pathogen cultures from 1 January 2020 to 31 December 2024 in LifeLabs BC microbiology regional laboratories, connected with 129 community collection centers. Only data from pediatric patients (age < 18 years) were included. We collected antimicrobial susceptibility testing (AST) results from the LifeLabs laboratory records. As per the Clinical and Laboratory Standard Institute (CLSI) guidelines, only data from patients’ initial visits in the entire study period was included to maximize accuracy of results; a minimum sample size of 30 isolates is needed to create an antibiogram [9]. When multiple microorganisms were identified as pathogens in a patient’s initial visit, all of these potential pathogen AST data were included in the current study analysis. Although viruses could also be causes of ear infections, they were not included in the current study, as antiviral susceptibility testing is not commonly performed in clinical laboratories nor required in clinical practice [8,10]. If viral testing is needed, polymerase chain reaction testing would be required that cannot generate culture and sensitivity results.

Because MEWS does not store full data prior to year 2020, only the most recent 5 years of data were included to generate for each antibiotic-microorganism combination and the most contemporary data [10]. The following microorganisms reached the minimum sample size of 30 isolates: methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, and Streptococcus pneumoniae. Haemophilus influenzae and Group A Streptococcus (GAS) did not meet the minimum sample size but were included in separate analyses. As per the CLSI M100 guidance, AST of Haemophilus influenzae are often unnecessary as empiric therapies with beta-lactams are often sufficient for respiratory infections; similarly, AST with penicillins and other beta-lactams does not need to be performed routinely as non-susceptible isolates have not been reported for Group A Streptococcus [11]. Additionally, not every microorganism isolate underwent AST as per the LifeLabs BC standard operating procedures. For instance, AST was not performed when standardized susceptibility testing was not available based on the CLSI guidance [11]. The current antibiogram project followed the LifeLabs BC ethical standards. No specific ethical board review was needed because the project was a retrospective audit and a quality improvement project that followed the CLSI M39 guidance and SQUIRE checklist (https://www.equator-network.org/wp-content/uploads/2012/12/SQUIRE-2.0-checklist.pdf; accessed on 1 June 2025), and it contained no patient-identifiable information. Creating antibiograms is a professional responsibility of a clinical microbiology laboratory [9].

2.2. Identification of Microorganisms in Ear Culture

The current study was a retrospective audit of ear specimens collected in 2020–2024. The common clinical practice was to use sterile culture swabs to take specimens from the patients’ ears for detection of microorganisms [10]. The ordering clinicians determined the indications for ear culture swabs on a case-by-case basis. The specimen samples were then inoculated on blood agar plates, chocolate agar plates, MacConkey agar plates, and colistin nalidixic acid plates at 35 °C at 5% carbon dioxide levels. The chocolate agar plates enhanced the growth of fastidious microorganisms; the MacConkey agar plates selected for Gram-negative bacilli such as Enterobacterales; and colistin nalidixic acid plates selected for Gram-positive microorganisms. The culture plates were incubated for 18 to 36 h. The identification of microorganism isolates followed a standard procedure using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) (Bruker Daltonics GmbH & Company KG, Bremen, Germany). If MALDI-TOF MS failed to identify the microorganism, the Vitek System (bioMerieux Incorporation, Durham, NC, USA) was also used to aid in the identification. As per the LifeLabs BC standard operating procedures, identification of potential pathogens would be reported, whereas alpha-hemolytic and non-hemolytic cocci, coagulase-negative staphylococci, and diphtheroids would be called normal flora (

Table 1. Common potential pathogens and normal flora microorganisms as per the LifeLabs British Columbia standard operating procedures.

Potential Pathogens

Normal Flora

Beta-hemolytic streptococci Candida albicans/Yeast not C. albicans Corynebacterium diphtheriae Fungus (including Aspergillus spp.) Gram negative bacilli Haemophilus influenzae Haemophilus parainfluenzae Moraxella catarrhalis Pseudomonas aeruginosa Staphylococcus aureus complex Staphylococcus intermedius Staphylococcus pseudintermedius Staphylococcus lugdunensis Streptococcus pneumonia Turicella otitidis

Alpha-hemolytic and non-hemolytic cocci Coagulase-negative staphylococci Diphtheroids

). If in doubt, microbiology technologists consulted microbiologists to determine whether an identified microorganism was a potential pathogen or normal flora.

2.3. Antimicrobial Susceptibility Testing (AST)

AST was reflexively performed for the identified potential pathogens mainly with the Vitek 2 automated AST system. Vitek 2 gave an approximation of minimum inhibitory concentration (MIC) based on real-time measurement of growth kinetics in antibiotic-containing microwells. When Vitek 2 failed to give the MIC, Kirby-Bauer disk diffusion and Epsilometer (E-test) methods were used as alternative methods. The interpretation of the AST results (susceptible, intermediate, resistant) was based on the breakpoints provided by CLSI M100 for the corresponding years [11]. Following the LifeLabs BC-standardized AST protocols, the antimicrobial agents routinely used to test the microorganism isolates were as follows: ampicillin, cephalothin/cephalexin, ciprofloxacin, clindamycin, cloxacillin, erythromycin, levofloxacin, penicillin, trimethoprim–sulfamethoxazole (TMP-SMX), and tetracycline. Cefoxitin and oxacillin AST were used to confirm the presence of MRSA [11]. For selected pathogens, such as MRSA, additional antimicrobials, such as vancomycin and linezolid, would be tested. As per CLSI guidance, selective antimicrobial testing data should be omitted in an antibiogram to prevent selection bias and were therefore not included in the current study analysis [9].

2.4. Statistical Analysis

GraphPad QuickCalcs (https://www.graphpad.com/quickcalcs/; accessed on 1 July 2025) was the software application used to perform statistical analyses. Categorical differences in sensitivity rates between antimicrobial agents were evaluated using two-tailed Chi-squared (χ²) tests and 95% confidence intervals. Statistical analyses were reported with χ² values, degrees of freedom (DF), and p-values; p < 0.05 was determined to be statistically significant. The Chi-squared test was chosen because that is one recommended statistical analysis recommended by CLSI guidance [9].

3. Results

Between 2020 and 2024, 2338 ear specimens with potential pathogens were processed at LifeLabs BC regional microbiology laboratories for culture. The most common microorganisms identified are listed in

Table 2. Incidence of the most common potential pathogens isolated in pediatric ear culture in LifeLabs British Columbia, 2020–2024.

Organism	Specimens (n)	% of Total Specimens
Total number of specimens	2338
Methicillin-susceptible Staphylococcus aureus	648	27.7
Group A Streptococcus	357	15.3
Pseudomonas aeruginosa	316	13.5
Turicella otitidis	111	4.8
Streptococcus pneumoniae	105	4.5
Methicillin-resistant Staphylococcus aureus	80	3.4
Haemophilus influenzae	75	3.2
Other microorganisms *	646	27.6

* Other microorganisms include yeast and filamentous fungus, Moraxella catarrhalis, Staphylococcus lugdunensis, and Enterobacterales. Culture plates with only normal flora and no growth were not considered pathogens and were therefore not captured in this table.

.

Table 3. Pediatric antibiogram for microorganisms that had antimicrobial susceptibility testing performed at least 30 times in LifeLabs British Columbia, 2020–2024. The data presents the mean of the percentage of susceptibility and the total number of isolates tested as the denominators.

	Antimicrobial Agents (% Susceptibility)
Organism	Cephalothin/Cephalexin	Erythromycin	Ciprofloxacin c	Clindamycin	Tetracycline	Trimethoprim/Sulfamethoxazole	Penicillin (Oral) d	Cloxacillin
Methicillin-susceptible Staphylococcus aureus	100% n = 640	82% n = 640	-	84% n = 640	97% n = 640	99% n = 640	-	100% n = 640
Pseudomonas aeruginosa	R b	R b	97% n = 149	R b	R b	R b	R b	R b
Turicella otitidis a	-	-	-	-	-	-	-	-
Streptococcus pneumoniae	-	91% n = 105	-	-	96% n = 105	92% n = 105	93% n = 105	-
Methicillin-resistant Staphylococcus aureus	R	50% n = 80	-	79% n = 80	85% n = 80	94% n = 80	R	R
	85–100% Susceptibility
	51–84% Susceptibility
	0–50% Susceptibility
R	Intrinsic Resistance

^a Susceptibility testing for Turicella otitidis was not routinely performed. Most clinical isolates of T. otitidis are resistant to clindamycin and erythromycin but susceptible to beta-lactams, ciprofloxacin, and tetracycline. ^b Pseudomonas aeruginosa is intrinsically resistant to a variety of antimicrobials including erythromycin, clindamycin, tetracycline, and trimethoprim–sulfamethoxazole. ^c Sensitivity data for ciprofloxacin against methicillin-susceptible Staphylococcus aureus and methicillin-resistant Staphylococcus aureus were not reported, as the number of isolates tested (<30) did not meet the minimum threshold recommended by Clinical and Laboratory Standard Institute for antibiogram-reporting. ^d The oral penicillin susceptible breakpoint (minimum inhibitory concentration of less than 0.06 microgram/milliliter) was used. As per CLSI, Streptococcus pneumoniae with this minimum inhibitory concentration is predictably susceptible to ampicillin and amoxicillin [11].

shows the antibiogram for microorganisms that had AST performed at least 30 times in this study period. Appendix A shows the antibiogram susceptibility data with 95% confidence intervals.

Table 4. Cumulative antimicrobial susceptibility test data of Group A Streptococcus isolated in pediatric ear culture in LifeLabs British Columbia, 2020–2024.

Antibiotics *		Penicillin	Levofloxacin	Clindamycin	Erythromycin
%Susceptible	n = 17	100%	100%	94%	94%

* Group A Streptococcus were only tested and reported if: requested or co-isolated with methicillin-resistant Staphylococcus aureus or penicillin allergy noted or patient on clindamycin or a macrolide. Please interpret the results with caution due to the small sample size (n < 30), which could be prone to selection bias.

and

Table 5. Cumulative antimicrobial susceptibility test data of Haemophilus influenza isolated in pediatric ear culture in LifeLabs British Columbia, 2020–2024.

Antibiotics *		Ampicillin
%Susceptible	n = 10	70%

* Antimicrobial susceptibility testing was not routinely performed for Haemophilus influenzae. Most isolates of H. influenzae are susceptible to cefuroxime, amoxicillin/clavulanate, levofloxacin and ciprofloxacin. Susceptibility to azithromycin and trimethoprim-sulfamethoxazole is variable. Please interpret the results with caution due to the small sample size (n < 30), which could be prone to selection bias.

show the cumulative antimicrobial susceptibility test data for Group A Streptococcus and Haemophilus influenzae, respectively. These microorganisms are not included in the antibiogram (Table 3) because each of them failed to reach the minimum sample size of 30 [9].

4. Discussion

4.1. Summary of the Findings

In this study, methicillin-susceptible Staphylococcus aureus was the most predominant organism found in the ear cultures (27.7%), followed by Group A Streptococcus (15.3%), Pseudomonas aeruginosa (13.5%), Turicella otitidis (4.8%), Streptococcus pneumoniae (4.5%), methicillin-resistant Staphylococcus aureus (3.4%), and Haemophilus influenzae (3.2%) (Table 2). Among the local incidences of organisms for the ear culture, there was a trend towards Gram-positive organisms (MSSA, Group A Streptococcus, Streptococcus pneumoniae, Turicella otitidis and MRSA), compared to Gram-negative organisms (Pseudomonas aeruginosa and Haemophilus influenzae). The high incidence of Staphylococcus aureus emphasized the importance of targeting this pathogen in empiric treatment. Our study also detected 43 Moraxella catarrhalis isolates, which were not among the most common isolates; none of the Moraxella catarrhalis isolates underwent AST and were therefore not included in the antibiogram.

In the antibiogram (Table 3), Streptococcus pneumoniae demonstrated high susceptibility to penicillin (93%), tetracycline (96%), TMP-SMX (92%) and erythromycin (91%). Haemophilus influenzae isolates showed only moderate susceptibility to ampicillin (70%). However, susceptibility testing was not routinely performed for Haemophilus influenzae; therefore, the data might be prone to selection bias. Among MSSA isolates, cloxacillin (100%), cephalothin/cephalexin (100%), TMP-SMX (99%), and tetracycline (97%) each significantly outperformed either clindamycin (84%) and erythromycin (82%). MRSA isolates retained high TMP-SMX susceptibility (94%), despite notable resistance to erythromycin (50%) and clindamycin (79%). Compared to MSSA, MRSA isolates demonstrated significantly lower susceptibility to erythromycin (82% vs. 50%, χ² 41.189, 1 DF, p < 0.0001). For MSSA, TMP-SMX demonstrated significantly higher susceptibility than tetracycline (99% vs. 97%, χ² 24.983, 1 DF, p < 0.05), even though the clinical significance of 2% difference might be trivial. For MRSA, TMP-SMX showed a trend of higher susceptibility than tetracycline (94% vs. 85%) but failed to reach statistical significance (χ² 3.225, 1 DF, p = 0.07)—this difference could be confirmed with a larger sample size in future studies.

Ciprofloxacin susceptibility for both MSSA and MRSA was excluded from the antibiogram due to an insufficient number of isolates tested (n < 30), which limited the reliability of the results. Pseudomonas aeruginosa remained highly susceptible to ciprofloxacin (97%). GAS isolates (n = 17) demonstrated universal susceptibility to penicillin (100%), which was not statistically different compared to clindamycin (94%, χ² 1.030, 1 DF, p = 0.3101) and erythromycin (94%, χ² 1.030, 1 DF, p = 0.3101) susceptibility (Table 4).

4.2. Clinical Significance

Pediatric ear infections represent a significant clinical burden. Acute otitis media is a global health concern, affecting over 200 million children worldwide, with the age-standardized incidence rate showing a slight increase [12]. Similarly, otitis externa also results in a substantial burden to the healthcare system, with the Centers for Disease Control and Prevention last updating the estimated annual rates of ambulatory care visits for acute otitis externa to be highest among children aged 5–9 years (18.6%) and 10–14 years (15.8%) [13]. This finding could be due to children’s weaker immune system and greater difficulty in draining out of fluid from the ear [14].

The results from this study highlighted the need for empiric antibiotic therapy tailored to the most prevalent pathogens in pediatric ear infections. The excellent susceptibilities of GAS (100%) and S. pneumoniae (93%) to penicillin support the use of narrow-spectrum beta-lactams for ear infections in community settings. Non-beta-lactam options such as macrolides (erythromycin) and lincosamides (clindamycin) were shown to be less reliable in the current study. Given these observations, narrow-spectrum beta-lactam antibiotics should remain first-line unless contraindicated. This supports existing guidelines that recommend amoxicillin as first-line therapy for acute otitis media [8]. However, the current study showed that Haemophilus influenza isolates were only 70% susceptible to ampicillin (Table 5). This result is from a selected small sample size (n = 10) and probably from cases with high pretest probability of resistance, because they were mainly performed per requests only for complicated clinical cases. Therefore, a larger sample size with routine testing would be needed to validate the finding.

The significant occurrence of MRSA in pediatric ear culture poses a challenge. Empiric therapy for patients with MRSA risks is complex because of the potential for complications if untreated. MRSA risk factors include recent or prolonged hospitalizations, weakened immune systems, and recent treatment with antibiotics [15]. Children presenting with more complicated or recurrent infections should be assessed for MRSA and treated with appropriate agents such as TMP-SMX due to its >90% susceptibility rate. The high efficacy of TMP-SMX and tetracycline against S. aureus suggested that these oral agents might be preferred where systemic treatment is required. For MSSA, TMP-SMX demonstrated significantly higher sensitivity than tetracycline (99% vs. 97%, χ² 24.983, 1 DF, p < 0.05), reinforcing its use. Tetracycline, despite high activity against S. aureus, is also limited by age-related contraindications of teeth discoloration in children under 8 years [16]. Tetracycline may still be considered in older children and non-severe infections when TMP-SMX is contraindicated. Compared to TMP-SMX, clindamycin and erythromycin demonstrated significantly lower sensitivity against MSSA (84%, χ² 93.197, 1 DF, p < 0.0001, and 82%, χ² 108.441, 1 DF, p < 0.0001, respectively); they even demonstrated lower sensitivity against MRSA (79%, χ² 6.019, 1 DF, p = 0.0142, and 50%, χ² 37.874, 1 DF, p < 0.0001, respectively). The use of clindamycin is further limited by gastrointestinal adverse events, including Clostridioides difficile infection, which can be harmful in young children [17,18]. The Canadian Pediatric Society emphasizes the importance of antibiotic stewardship to reduce C. difficile risk in pediatric patients, encouraging careful consideration before its use in this population [17].

The high prevalence of MSSA in ear culture supported the empiric use of beta-lactams in children without MRSA risk factors. Compared to non-beta-lactam alternatives such as clindamycin or macrolides, beta-lactams are also less likely to promote resistance or contribute to adverse events like C. difficile infection [18].

4.3. Comparison with Other Studies

The microbial profile and susceptibility patterns in this study are largely consistent with evidence from previous investigations of pediatric ear infections. Staphylococcus aureus and Pseudomonas aeruginosa were among the most frequently isolated organisms, aligning with outcomes from international studies. For instance, a Turkish outpatient study identified S. aureus and P. aeruginosa as the predominant pathogens in ear swab cultures, while a Brazilian investigation similarly reported these two organisms as the leading causes of acute otitis externa [19,20]. The same study also found 95% susceptibility of P. aeruginosa to ciprofloxacin and demonstrated activity of cephalosporins against S. aureus, consistent with our results [20].

Regarding MRSA in pediatric ear infections, our findings of >90% susceptibility to TMP-SMX aligned with data from a Korean cohort study exhibiting excellent TMP-SMX activity even in community-associated MRSA strains, while resistance to clindamycin and erythromycin was notably elevated [21]. A retrospective review of children with tympanostomy tube otorrhea attributed to MRSA similarly reported high resistance rates to clindamycin and fluoroquinolones, further supporting TMP-SMX as a preferred oral option [22].

Previous clinical studies have reported approximately 95% susceptibility of community-onset MRSA isolates to tetracyclines for skin and soft tissue infections, also supporting their use as an oral treatment option [23]. In comparison, our study found an 85% susceptibility rate among pediatric ear culture isolates. Additionally, tetracyclines are generally not recommended in young children due to risks such as dental staining and effects on bone growth under 8 years of age [16]. Our study showed that TMP-SMX might be more suitable, with less likelihood of adverse effects in children.

4.4. Strength and Limitations

This study was based on local community-focused pediatric ear culture data, providing real-world insights into the prevalence and antimicrobial susceptibility patterns of key otitis pathogens in BC. This is an area which is generally underrepresented in existing literature. Most antibiogram studies aggregate data across all age groups or focus on solely hospitalized populations, therefore overlooking community-level resistance patterns in children [4,5,6]. By focusing exclusively on a pediatric population, the findings are relevant to clinicians treating ear infections including otitis media and otitis externa in children, a demographic to whom these results most directly apply. Our analysis enables nuanced treatment recommendations and supports the use of narrow-spectrum agents for appropriate infections. Additionally, the study highlights the increasing role of MRSA in ear infections, advocating for more tailored therapeutic options. Although intravenous vancomycin is likely to cover MRSA, it is not always practical in community settings. The current study showed there are feasible oral options for MRSA like TMP-SMX. These results may help inform local prescribing guidelines and improve patient outcomes in pediatric otitis.

The limitations of our research include the underrepresentation of the susceptibility data of certain organisms such as M. catarrhalis and T. otitidis. Due to not being routinely tested at LifeLabs, the limited sample size prevented reliable statistical interpretation about their role in pediatric ear infections. AST methods for Moraxella catarrhalis are listed in CLSI M45 Methods for Antimicrobial Dilution and Disk Susceptibility Testing of Infrequently Isolated or Fastidious Bacteria [24]. This AST is not recommended routinely in clinical laboratories; AST may be useful mainly for treatment of prolonged or severe infections. AST methods of Turicella species are also listed in the CLSI M45. As per the guidelines, Turicella species are coryneform bacteria frequently encountered as contaminants in cultures; testing of isolates from normally sterile sources may be warranted that do not include ear specimens.

Like other published antibiograms, the absence of clinical info also precluded any correlation between microbiologic findings and patient outcomes. We could not be confident about factors such as if patients had drainage or if the microorganisms isolated represented true pathogens or normal flora. As a retrospective analysis, the study might be subject to inherent biases in specimen collection and selection, including the underrepresentation of pathogens not typically cultured in otitis media without perforation. The retrospective nature of the analysis could not allow correlation with clinical efficacy of the antibiotics which patients received. Because of the lack of clinical information available in the test orders, the study could not determine the clinical diagnosis and the details of the anatomical site of collection, which are common limitations of antibiograms. Patients’ past medical history, prior antimicrobial uses, and risk factors for infections with multidrug-resistant microorganisms might have all played a role in the current findings. To minimize these confounder effects, only data from patients’ initial visits in the entire study period was included, as per CLSI guidance [9]. The current study’s analysis of a large sample size of 2338 ear specimens in 5 years might help to reduce selection bias due to random chance.

Furthermore, the study data may not be generalizable to hospital-based settings. The data was derived solely from outpatient samples and thus did not capture pathogen profile in hospitalized children where microbial trends may differ substantially. This study was conducted within a single province, limiting the generalizability of findings to other geographic regions. Different resistance patterns and prescribing in other provinces prevents the extrapolation of our results beyond the local setting. Of note, CLSI provides no minimum inhibitory concentration breakpoints for topical antimicrobials, because drug concentration at target site is unpredictable [11].

4.5. Future Studies

Future research should focus on longitudinal studies to monitor antimicrobial resistance trends over time, especially in the context of the changing epidemiology of ear infections in pediatric populations. We want to encourage other institutions to conduct similar retrospective audits in other geographical areas and monitor the trends of resistance. Prospective, multicenter surveillance would also help to establish whether the resistance patterns observed in this community-based pediatric population are consistent across broader spectrums, or if regional variability exists due to differences in prescribing practices and population demographics. With a larger sample size, analysis could be made to determine the trend of resistance between different years and regions. Ongoing development and application of pediatric-focused antibiograms will be essential to support antimicrobial stewardship and optimize treatment strategies in both outpatient and inpatient pediatric care settings.

5. Conclusions

This study evaluated pathogens and their antimicrobial susceptibility profiles in pediatric ear infections within an outpatient setting. The predominance of Gram-positive organisms, such as S. aureus, GAS, and S. pneumoniae, suggests these are common pathogens in ear infections. The high susceptibility of S. pneumoniae and GAS to beta-lactam antibiotics reinforces the first-line role of these agents in treatment of ear infections. Among S. aureus isolates, MSSA accounted for the majority and demonstrated favorable susceptibility to cloxacillin, first-generation cephalosporins, tetracycline, and TMP-SMX. This establishes the use of narrow-spectrum oral beta-lactams such as amoxicillin for empiric therapy when MRSA is not suspected. TMP-SMX may be considered for patients infected with MRSA.