European Journal of Cardiovascular Medicine

Staphylococcus aureus (S. aureus) predominantly colonizes sites such as the anterior nares, axillae and perineum and is present in approximately 20-40% of adults which clearly highlights its ubiquity and potential as a reservoir for infection.[1,2] Globally, it causes a spectrum of diseases from skin and soft-tissue infections to severe conditions like sepsis and toxic shock syndrome.[3] Its pathogenesis is facilitated by various cell-surface and secreted virulence factors, along with its remarkable adaptability to antibiotic resistance.[4,5] Initially, penicillin was effective for treating S. aureus infections; however, with the evolution of β-lactamase-producing strains, resistance to penicillin became widespread.[6,7] This resistance pattern continued to escalate with the introduction of methicillin-resistant S. aureus (MRSA) strains in the 1960s.[8] Since then, MRSA has become a formidable public health concern, with multidrug-resistant strains necessitating the use of last-resort treatments like vancomycin.[9]

In recent years, MRSA has been classified into two epidemiological categories: HA-MRSA and CA-MRSA.[10] HA-MRSA infections are typically acquired in healthcare settings and are associated with risk factors like prolonged hospital stays, invasive procedures, and previous antibiotic exposure.[11] Conversely, CA-MRSA infections occur in otherwise healthy individuals without healthcare exposure and tend to exhibit susceptibility to a broader range of antibiotics compared to HA-MRSA.[12] CA-MRSA strains frequently harbor genes encoding the Panton-Valentine leukocidin (PVL), a virulence factor that promotes aggressive tissue destruction.[13] The genetic divergence between HA-MRSA and CA-MRSA underpins their differences in virulence and antibiotic susceptibility patterns, with CA-MRSA often displaying limited multidrug resistance relative to HA-MRSA.[13]

The incidence of MRSA infections in India, particularly in tertiary care hospitals, underscores the public health threat posed by this pathogen.[14] Reports from various Indian states indicate a high prevalence of both HA-MRSA and CA-MRSA.[15,16] However, local comparative data on the prevalence and susceptibility patterns of HA-MRSA and CA-MRSA in West Bengal remain limited, reflecting a critical gap in the knowledge necessary for formulating targeted antimicrobial policies. This gap underscores the need for localized data to facilitate clinical and public health decisions, especially as multidrug-resistant MRSA isolates continue to emerge.

This study aimed to comprehensively compare the prevalence and antimicrobial susceptibility patterns of HA-MRSA and CA-MRSA in a tertiary care hospital in West Bengal. By characterizing these patterns, this cross-sectional study using laboratory-based susceptibility testing will help identify the most effective antibiotics and guide local MRSA management strategies. 

Study setting

This study was conducted at the Microbiology Department of Burdwan Medical College and Hospital in West Bengal, India. The hospital serves a diverse population in both rural and urban settings, offering a broad clinical spectrum of patients. Geographically, the region has a humid subtropical climate, which may influence the prevalence of skin and soft tissue infections, including Staphylococcus aureus colonization. The hospital handles both community-based and healthcare-associated infections and provides a comprehensive platform to compare the two MRSA strains. This regional context is crucial for interpreting and extrapolating results to similar healthcare settings in India.

Study design

We conducted a hospital based cross-sectional study.

Study population

Inpatients and outpatients, regardless of age and sex, across various medical and surgical departments of Burdwan Medical College and Hospital in West Bengal, India, submitted clinical samples to our department from which Staphylococcus aureus was isolated.

Sample size

The study, which was conducted over a nine-month period comprised of 694 unique isolates of Staphylococcus aureus.

Study procedure

In this study, detailed patient information, including the duration of hospital admission, presenting symptoms, and any prior hospitalizations or surgeries, was carefully recorded before sample collection. Antimicrobial susceptibility testing was performed of all clinical isolates of  Staphylococcus aureus using the Kirby-Bauer disk diffusion method using azithromycin (10 μg), ciprofloxacin (5 μg), levofloxacin (300 μg), clindamycin (2 µg), cotrimoxazole (25 μg ), doxycycline (30 μg ) amikacin (30 µg), netilmicin (30  μg), gentamicin (10 μg), ceftriaxone (10 μg) vancomycin (30 µg), linezolid (30 µg), teicoplanin (30 µg), amoxicillin clavulanic acid (20/10 μg), and nitrofurantoin (300 µg).[17]

Detection of MRSA

MRSA was detected using a cefoxitin (30 µg) disc. An inhibition zone of 22 mm or greater indicated cefoxitin susceptibility, classifying the Staphylococcus aureus isolate as methicillin-sensitive. Isolates with inhibition zones of 21 mm or smaller were classified as methicillin-resistant.[17]

Characterization of MRSA

The MRSA isolates were classified as community-acquired or hospital-acquired based on the patient’s history. All infections occurring among the out patients or inpatients with an MRSA isolate earlier than 48 hours of hospitalisation, would be considered as CAMRSA and HA-MRSA is called when MRSA was isolated from a patient after 48 hours of hospitalisation or from a patient with a history of hospitalisation for surgery or dialysis, or of a residence in a long term care facility within 1 year of the MRSA culture date.[18]

Data collection

Clinical data, including patient demographics, medical and surgical history, duration of admission, and infection site, were recorded using standardized case report forms. Laboratory data were recorded using this form.

Data entry was conducted using Microsoft Excel, and the entered data were cross-verified by a second researcher for accuracy.

Data validation involved automated checks within the database to flag outliers or missing data and ensure completeness and consistency. In addition, double-entry verification was performed in 5% of the records.

These structured tools and techniques for data collection, entry, and validation were integral to achieving robust and reproducible findings that are essential for the accurate comparative analysis of healthcare-associated and community-associated MRSA isolates.

Data analysis

Demographic characteristics and symptom profile were summarized as frequencies and percentages. All statistical analyses were done using SPSS v.16.0 software (SPSS Inc., USA). The antimicrobial susceptibilities of CA- and HA-MRSA strains were compared using the chi-square test. A p value < 0.05 was considered statistically significant.

Human participant protection

This study was approved by the Institutional Human Ethics Committee (IHEC) of the Burdwan Medical College, West Bengal. Informed consent was obtained from all participants to ensure privacy and confidentiality. The study strictly adhered to the approved protocol with no deviations.

Demographic characteristics

A total of 285 MRSA isolates were analyzed, with 94 (33%) classified as community-associated MRSA (CA-MRSA) and 191 (67%) as healthcare-associated MRSA (HA-MRSA). The median age of patients was comparable across groups, with CA-MRSA patients having a median age of 42 years (range: 21–73) and HA-MRSA patients 47 years (range: 20–74) (p = 0.79).

Regarding sex distribution, male patients predominated overall, accounting for 179 (62.8%) of the total MRSA cases. Among the CA-MRSA cases, 67 (71.3%) were male, compared to 112 (58.6%) in HA-MRSA (p = 0.0502). Of the total MRSA cases, 106 (37.2%) were female, with a higher proportion in the HA-MRSA group (79/191; 41.4%) than in the CA-MRSA group (27/94; 28.7%) (Table 1).

Table 1: Demographic characteristics of patients having MRSA isolates

Distribution of MRSA from different clinical samples

Of the 285 MRSA isolates, the most common sample source was pus, accounting for 92 cases (32.3%), with a similar distribution of CA-MRSA (31/94; 32.97%) and HA-MRSA (61/191; 31.9%) (p < 0.05). Wound swabs were the second most frequent source, contributing to 88 isolates (30.9%). This trend was consistent across CA-MRSA (30/94, 31.9%) and HA-MRSA (58/191, 30.4%) (p < 0.05).

Blood samples yielded 56 isolates (19.6%), with 17 (18.1%) in the CA-MRSA group and 39 (20.4%) in the HA-MRSA group (p < 0.05). Urine samples accounted for 49 cases (17.2%), which was nearly equally distributed between CA-MRSA (16/94; 17.02%) and HA-MRSA (33/191; 17.3%) (p < 0.05) (Table 2).

Table 2: Distribution of MRSA in different clinical samples

Antimicrobial susceptibilities of HA -MRSA and CA- MRSA isolates

Antimicrobial susceptibility patterns revealed notable differences between healthcare-associated MRSA (HA-MRSA, n=191) and community-associated MRSA (CA-MRSA, n=94). Vancomycin, Linezolid, and Teicoplanin showed universal efficacy (100% susceptibility in both the groups). Clindamycin was more effective against HA-MRSA (91.6%, 175/191) than CA-MRSA (79.7%, 75/94, p<0.05). Similarly, Amikacin demonstrated higher susceptibility to CA-MRSA (61.7%, 58/94) than to HA-MRSA (17.3%, 33/191, p<0.05). In contrast, ciprofloxacin showed limited activity, with 35.1% (33/94) susceptibility in CA-MRSA and 6.3% (12/191) in HA-MRSA (p<0.05).

Although Nitrofurantoin and Gentamicin displayed comparable susceptibility in both groups (p>0.05), ceftriaxone exhibited significantly lower effectiveness, particularly against HA-MRSA (3.6%, 7/191, p<0.05) (Table 3).

Table 3. Antimicrobial susceptibilities of HA-MRSA and CA-MRSA isolates.

S^1: Sensitive, R²: Resistant. ³P value: The resistance rates of antibiotics among CA-MRSA compared with those among HA-MRSA

We analyzed the prevalence and antimicrobial susceptibility patterns of 285 MRSA isolates, distinguishing between healthcare-associated (HA-MRSA) and community-associated (CA-MRSA) strains. We observed differences in sample sources and antimicrobial resistance profiles between the two groups. These findings align with existing literature, which reports varying prevalence rates and resistance patterns across different regions and settings.[19] Notably, the universal efficacy of vancomycin, linezolid, and teicoplanin against both MRSA types underscores their continued relevance in treatment protocols. The observed differences in susceptibility to other antibiotics, such as clindamycin and amikacin, warrant further investigation to inform targeted therapeutic strategies.[20]

Prevalence and Demographics

HA-MRSA accounted for 67% (191/285) of the isolates, whereas CA-MRSA comprised 33% (94/285). This higher prevalence of HA-MRSA aligns with studies from other regions in India, indicating a substantial presence of HA-MRSA in hospital settings.[20]The median ages of the CA-MRSA and HA-MRSA patients were 42 and 47 years, respectively, with no statistically significant difference (p = 0.79). Male patients predominated in both groups, particularly in the CA-MRSA cohort, where 71.3% were male compared with 58.6% in the HA-MRSA group (p = 0.0502). This male predominance is consistent with other studies reporting higher MRSA infection rates among males.[19]

Sample Sources

Pus samples were the most common source of MRSA isolates (32.3%), with similar distributions of CA-MRSA (32.97%) and HA-MRSA (31.9%) (p < 0.05). Wound swabs were the second most frequent source (30.9%), followed by blood (19.6%) and urine (17.2%) samples, with comparable distributions between the two groups. The predominance of pus and wound swab isolates suggests that skin and soft tissue infections are major manifestations of MRSA, corroborating findings from other studies.[21]

Antimicrobial Susceptibility Patterns

Both CA-MRSA and HA-MRSA isolates exhibited 100% susceptibility to vancomycin, linezolid, and teicoplanin, underscoring their continued efficacy against MRSA infection. Clindamycin was more effective against HA-MRSA (91.6%) compared to CA-MRSA (79.7%) (p < 0.05), a finding that contrasts with some studies reporting higher clindamycin resistance in HA-MRSA.[22] Amikacin showed a higher susceptibility to CA-MRSA (61.7%) than to HA-MRSA (17.3%) (p < 0.05), which is consistent with reports that CA-MRSA strains are generally more susceptible to non-β-lactam antibiotics. [23] Ciprofloxacin exhibited limited activity, with only 35.1% susceptibility in CA-MRSA and 6.3% in HA-MRSA (p < 0.05), reflecting widespread resistance to fluoroquinolones among MRSA isolates.[20] Nitrofurantoin and gentamicin displayed comparable susceptibility in both groups (p > 0.05), whereas ceftriaxone was notably ineffective, particularly against HA-MRSA (3.6%) (p < 0.05), which is consistent with the significant resistance of MRSA to β-lactam antibiotics.

Implications of the findings

The comparable median ages and male predominance in both groups suggest that MRSA infections affect a broad demographic, necessitating targeted infection control measures across all age groups and sexes. The predominance of pus and wound swab isolates indicates that skin and soft tissue infections are the major manifestations of MRSA, highlighting the need for effective wound care management. The observed differences in antimicrobial susceptibility patterns between CA-MRSA and HA-MRSA underscore the importance of the accurate classification of MRSA strains to guide appropriate antibiotic therapy. The unexpected finding of higher clindamycin susceptibility in HA-MRSA than in CA-MRSA warrants further investigation to understand the underlying mechanisms and potential implications for treatment strategies.

Strengths of the study

This study was conducted in a tertiary care hospital in West Bengal, and included healthcare-associated (HA-MRSA) and community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA). This research was feasible owing to its single-centre design, which ensured controlled data collection. It provided updated insights specific to West Bengal, addressing a gap in localized epidemiological data, especially given the region's high MRSA prevalence of 43%. [19] The findings are pertinent for informing local infection control policies and treatment protocols, considering the significant burden of MRSA infections in India.[24]

Limitations of the study

The limitations of this study include its single-centre design, which may restrict the applicability of the findings to other settings. A small sample size could have undermined the statistical power, affecting the reliability of the results. Temporal factors, such as data collection during a specific period, may not capture evolving MRSA prevalence and resistance patterns. Additionally, the lack of molecular typing prevents differentiation between MRSA clones, limiting insights into the transmission dynamics and resistance mechanisms. Future studies should address these limitations by expanding the sample size, incorporating multicenter data, and utilizing advanced methodologies for greater validity.

Our study revealed a higher prevalence of healthcare-associated MRSA (HA-MRSA) than community-associated MRSA (CA-MRSA) in our tertiary care hospital in West Bengal. Both HA-MRSA and CA-MRSA isolates exhibited significant resistance to multiple antibiotics, underscoring the need for ongoing surveillance and development of targeted infection control strategies to effectively manage MRSA infections. This conclusion aligns with findings from other studies in India that reported varying prevalence rates of MRSA across different regions. For instance, a systematic review and meta-analysis highlighted the endemic nature of MRSA in India, emphasizing the importance of early detection and tailored treatment strategies.[19] Additionally, research from a rural hospital in Bankura, West Bengal, reported a higher prevalence of HA-MRSA than CA-MRSA, with both types showing considerable resistance to commonly used antibiotics. [21]These findings highlight the critical need for continuous monitoring of MRSA prevalence and antimicrobial susceptibility patterns, particularly in tertiary care settings. Implementing effective infection control measures and developing region-specific treatment guidelines are essential steps toward mitigating the impact of MRSA infections in healthcare facilities. This study highlights HA-MRSA's higher resistance and nosocomial prevalence, while CA-MRSA has distinct epidemiological and clinical traits, emphasizing the need for tailored prevention and treatment strategies in different healthcare and community settings.

Conflicts of Interest

The authors have no conflicts of interest to declare.

Acknowledgement

I express my heartfelt thanks and gratitude to the administration, faculty members and staffs of department of Microbiology, Burdwan medical college and hospital for allowing and supporting me to conduct the study.

Funding

The study was funded by the authors.

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