Septicemia, also referred to as bloodstream infection (BSI), is a major cause of morbidity and mortality worldwide, particularly in critically ill patients, neonates, elderly individuals, and immunocompromised hosts¹. Rapid identification of the causative pathogen is essential for prompt initiation of targeted antimicrobial therapy, which is directly associated with improved patient outcomes and reduced healthcare costs².

Blood culture remains the cornerstone for laboratory diagnosis of septicemia and guides antimicrobial stewardship by enabling pathogen identification and antimicrobial susceptibility testing³. The conventional manual blood culture method has been used for decades and involves inoculation of blood into enrichment media followed by periodic subcultures and visual inspection for turbidity or hemolysis. Despite its widespread use, this method has several limitations, including delayed detection, increased manual handling, higher contamination risk, and reduced sensitivity, particularly in patients receiving prior antibiotic therapy⁴.

Advancements in microbiological diagnostics have led to the development of automated blood culture systems, such as BACTEC, BacT/ALERT, and VersaTREK, which utilize continuous monitoring of microbial growth by detecting metabolic byproducts such as carbon dioxide⁵. These systems allow earlier detection of positive cultures, improved recovery of fastidious organisms, and reduced labor requirements. Additionally, automated systems have built-in alerts and standardized incubation conditions, thereby minimizing human error⁶.

Several studies have demonstrated that automated blood culture systems significantly reduce the time to detection of pathogens compared to conventional methods, which is crucial for early clinical decision-making⁷. Early detection facilitates rapid de-escalation or escalation of antimicrobial therapy, thus reducing the emergence of antimicrobial resistance⁸. Moreover, automated systems have shown better performance in detecting low-level bacteremia and fungemia, conditions that are often missed by conventional techniques⁹.

However, the high initial cost of automated systems and consumables limits their widespread adoption in resource-limited settings, where conventional methods are still predominantly used¹⁰. Therefore, comparative studies evaluating the performance of manual conventional blood culture techniques against automated systems are essential to justify their implementation and to assess their clinical utility in diverse healthcare settings.

The present study aims to compare conventional manual blood culture methods with an automated blood culture system in terms of culture positivity rate, time to detection, spectrum of microbial isolates, and contamination rates in patients with suspected septicemia.

This was a prospective, comparative study conducted over a period of 12 months in the Department of Microbiology of a tertiary care teaching hospital. Ethical approval was obtained from the Institutional Ethics Committee prior to study initiation.

Study Population

Patients of all age groups clinically suspected of septicemia and admitted to intensive care units, medical wards, surgical wards, and neonatal units were included in the study.

Inclusion Criteria

• Patients with clinical features suggestive of septicemia such as fever, hypothermia, tachycardia, hypotension, altered sensorium, or leukocytosis
• Patients with suspected bloodstream infection prior to initiation of antimicrobial therapy
• Patients willing to provide informed consent (or consent from guardians in pediatric cases)

Exclusion Criteria

• Patients already on prolonged antibiotic therapy (>72 hours)
• Inadequate blood sample volume
• Hemolyzed or improperly collected samples
• Repeat samples from the same patient within 48 hours

Sample Collection

Under strict aseptic precautions, 10 mL of blood was collected from adults and 1–3 mL from pediatric patients. The sample was divided equally for inoculation into conventional blood culture bottles and automated blood culture bottles.

Conventional Blood Culture Method

Blood was inoculated into brain heart infusion (BHI) broth in a 1:10 ratio and incubated aerobically at 37°C. Bottles were inspected daily for turbidity, gas production, or hemolysis. Subcultures were performed at 24 hours, 48 hours, 72 hours, and on day 7 onto blood agar and MacConkey agar plates. Cultures were reported negative after 7 days if no growth was observed.

Automated Blood Culture System

Blood samples were inoculated into automated culture bottles and loaded into the automated blood culture instrument, which continuously monitored microbial growth. Positive signals were flagged automatically, and subcultures were performed immediately.

Identification and Antimicrobial Susceptibility Testing

Isolates were identified using standard biochemical tests, and antimicrobial susceptibility testing was performed by Kirby-Bauer disc diffusion method as per CLSI guidelines.

Statistical Analysis

Data were analyzed using statistical software. Culture positivity rates were compared using the chi-square test, and time to detection was expressed as mean ± SD. A p-value <0.05 was considered statistically significant.

Table 1. Demographic Distribution of Study Participants

                                                                       Majority of suspected septicemia cases were observed in adult patients.

Table 2. Culture Positivity Rate

                                                            Automated blood culture system showed a significantly higher positivity rate.

Table 3. Time to Detection of Growth

Automated system significantly reduced time to detection.

Table 4. Distribution of Microorganisms Isolated

Gram-negative organisms predominated in both methods.

Table 5. Detection of Fastidious Organisms

Automated system showed improved detection of fastidious organisms.

Table 6. Contamination Rates

Automated blood culture systems had lower contamination rates.

Gram Positive Organisms isolated include: Staphylococcus aureus, most common, followed by Streptococcus species, CoNS, Enterococcus sp.

Gram Negative organisms isolated include: Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter, Enterobacter sp, Salmonella sp.

Fungi isolated include: Candida albicans, most common, followed by Candida tropicalis and Histoplasma

The present study highlights the superiority of automated blood culture systems over conventional manual methods in diagnosing septicemia. The higher positivity rate observed with automated systems is consistent with previous studies that reported enhanced microbial recovery due to continuous monitoring and optimized growth conditions¹¹–¹³.

A significant reduction in time to detection was noted with automated systems, which is crucial for early initiation of appropriate antimicrobial therapy. Similar findings have been reported by Patel et al. and Banerjee et al., who demonstrated a reduction of up to 48 hours in pathogen detection time¹⁴,¹⁵. Early detection not only improves patient survival but also reduces hospital stay and healthcare costs¹⁶.

Gram-negative bacteria were the predominant isolates in this study, aligning with the changing epidemiology of septicemia in developing countries¹⁷. The improved detection of fastidious organisms by automated systems may be attributed to enriched media and continuous agitation, which support microbial growth even at low inoculum levels¹⁸.

Lower contamination rates observed in automated systems can be attributed to minimal manual handling and standardized protocols, a finding supported by several multicentric studies¹⁹,²⁰. Reduced contamination minimizes false-positive results and unnecessary antibiotic use.

Despite these advantages, the higher cost of automated blood culture systems remains a challenge in resource-limited settings. However, considering the clinical benefits, reduced labor, and improved patient outcomes, their cost-effectiveness in the long term is justifiable²¹,²².

Overall, the findings of this study are in concordance with global literature supporting the transition toward automated blood culture systems as the standard of care for diagnosing septicemia.

Automated blood culture systems outperform conventional manual methods in terms of sensitivity, rapidity, and reliability for diagnosing septicemia. Their adoption in clinical microbiology laboratories can significantly enhance early pathogen detection, guide appropriate antimicrobial therapy, and improve patient outcomes.

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