A hospital-based cross-sectional study was conducted over a period of 18 months at the Department of Medicine and Microbiology in a tertiary care teaching hospital in India. The study aimed to determine the prevalence of subclinical bacteremia among patients with prosthetic heart valves during routine follow-up.

Study Population: Patients aged 18 years and above who had undergone prosthetic heart valve replacement (either mechanical or bioprosthetic) at least 6 months prior and were attending the cardiology outpatient department for routine follow-up were included in the study.

Inclusion Criteria:

• Adults (≥18 years) with a documented history of prosthetic heart valve implantation.
• Asymptomatic at the time of enrollment (i.e., absence of fever, malaise, or clinical signs of infective endocarditis).
• Provided informed written consent.

Exclusion Criteria:

• Patients on antibiotic therapy within the past two weeks.
• Known or suspected active infection at any site.
• History of hospitalization or invasive dental/surgical procedures in the preceding four weeks.
• Immunocompromised patients (e.g., HIV-positive, on chemotherapy, or long-term steroids).

Sample Collection and Microbiological Analysis: From each participant, two peripheral venous blood samples (5–10 mL each) were collected aseptically and inoculated into brain-heart infusion broth for aerobic and anaerobic culture. The blood cultures were incubated and monitored using an automated culture system for up to 7 days. Positive cultures were subcultured on blood and MacConkey agar, and organisms were identified using standard biochemical tests and automated identification systems. Antibiotic sensitivity was performed following Clinical and Laboratory Standards Institute (CLSI) guidelines.

Data Collection and Analysis: Demographic details, clinical history, type of prosthetic valve, time since surgery, and comorbid conditions were recorded using a pre-structured proforma. Data were analyzed using SPSS. Descriptive statistics were used to determine the prevalence of subclinical bacteremia. Chi-square or Fisher’s exact test was applied to explore associations between bacteremia and patient characteristics. A p-value of <0.05 was considered statistically significant.

This cross-sectional study was conducted in 100 patients from the Cardiology OPD & Heart failure Clinic of ABVIMS and Dr. RML Hospital, New Delhi from September 2022 to December 2023.

Inclusion criteria were age > 18 years and LVEF < 40%.Exclusion criteria were no hospitalisation for decompensated heart failure in last 6 months,Class IV NYHA patients,chronic kidney disease stage 4 and 5,pregnancy and preexiting chronic  lung disease on treatment.

Detailed history and clinical examination were done. Data of demographic characteristics, comorbidities,body mass index, smoking status and functional capacity assessed by New York Heart Association (NYHA) functional classification were done for all patients.

All patient undergone routine blood tests, X-ray chest, electrocardiogram and 2D Echocardiography.

The transthoracic echocardiographic study was conducted according to the recommendations from the American Society of Echocardiography. LV ejection fraction was calculated from the LV end-diastolic volume and end-systolic volume estimates by biplane Simpson method.

Pulmonary function test was performed using spirometry according to the American Thoracic Society standards.After a 5-minute rest in a seated position, spirometric parameters were measured.The predicted values were calculated using validated spirometric prediction equations, and  FVC, and forced expiratory volume in the first second (FEV1) are presented as the percentage of their relevant predicted values. The ventilatory abnormalities were further categorized into 3 types: obstructive type is defined as FEV1/FVC <70% and FVC ≥80% of the predicted value; restrictive type is defined as FEV1/FVC ≥70% and FVC <80% of the predicted value; mixed type is  defined as FEV1/FVC <70% and FVC <80% of the predicted value.The severity of respiratory abnormality was graded as per American Thoracic Society Grades for Severity of a Pulmonary Function Test Abnormality[8].

Statistical Analysis

Descriptive statistics were reported in the form of means/standard deviations and medians/IQRs for continuous variables and frequencies and percentages for categorical variables. Group comparisons for continuously distributed data were performed using an independent student "t" test when comparing two groups. If data was found to be non-normally distributed, appropriate non-parametric test in the form of Wilcoxon Test was used. Three or more group comparisons done with ANOVA(parametric) or Kruskal Wallis test(non-parametric).

Chi-squared test was used for group comparisons for categorical data. If the expected frequency in the contingency tables was found to be <5 for >25% of the cells, Fisher's exact test was used instead.

Linear correlation between two continuous variables was examined using Pearson's correlation (if data were normally distributed) and Spearman's correlation (for non-normally distributed data).All the reported p-values are two-sided and p-values <0.05 were considered to indicate statistical significance. SPSS v28 (IBM Corp.) was used for data analysis.

The present cross-sectional study evaluated 120 patients with prosthetic heart valves to assess the prevalence and associated factors of subclinical bacteremia. The demographic and clinical characteristics are summarized in Table 1. The majority of participants were aged between 46 and 60 years, with a slight male predominance. Most patients had mechanical valves, and mitral valve replacements were more common than aortic or double valve replacements. Notably, over 40% of patients had undergone valve replacement surgery more than three years prior. A significant proportion also had comorbid conditions, particularly hypertension and diabetes mellitus.

As shown in Table 2, the prevalence of subclinical bacteremia in the study population was 10%. While the majority of patients had no evidence of bacteremia, a non-negligible proportion demonstrated positive blood cultures despite being asymptomatic, highlighting the potential risk of silent bloodstream infections in this high-risk group.

Table 3 details the microbiological spectrum observed in patients with positive blood cultures. Coagulase-negative Staphylococci were the most frequently isolated organisms, followed by Streptococcus viridans and Enterococcus faecalis. These findings are consistent with the skin and oropharyngeal flora, indicating potential routes of bacteremia in prosthetic valve recipients.

Table 4 presents the analysis of clinical variables associated with bacteremia. There was a statistically significant association between bacteremia and a shorter interval since valve replacement surgery (p = 0.045), as well as the presence of diabetes mellitus (p = 0.028). No significant association was observed between the type of prosthetic valve and bacteremia. These findings suggest that patients with recent surgery and comorbid diabetes may require closer monitoring for subclinical infections.

Table 1: Demographic and Clinical Profile of the Study Participants (N = 120)

Table 2: Prevalence and Pattern of Subclinical Bacteremia (N = 120)

Table 3: Microorganisms Isolated in Positive Blood Cultures (n = 12)

Table 4: Association between Clinical Variables and Bacteremia (N = 120)

*Significant at p < 0.05

Figure 1: Microorganisms Isolated from positive blood cultures

This study documents a 10% prevalence of subclinical bacteremia among asymptomatic patients with prosthetic heart valves, highlighting the potential for occult bloodstream infection even in the absence of clinical symptoms. While data on subclinical bacteremia in prosthetic-valve recipients is limited, our findings align with existing literature demonstrating that coagulase-negative staphylococci (CoNS), Streptococcus viridans, and Enterococcus species are common isolates in prosthetic valve endocarditis and silent bacteremia alike [6,7]. These organisms flourish in the biofilm-rich environment of prosthetic material and may persist without overt infection according to registry data [7].

Patients with recent valve surgery (<1 year) and diabetes mellitus were significantly more likely to demonstrate positive cultures. This echoes observations that early postoperative bacteremia and comorbid diabetes increase the risk of prosthetic valve endocarditis (PVE) and subclinical infection [6]. Recognizing these associations is critical for guiding surveillance strategies in high-risk groups, as these silent infections may progress to overt PVE with high morbidity and mortality [8,9].

Prior studies have reported PVE prevalence ranging from 1% to 6% of all prosthetic valve recipients, with culture-negative cases particularly prevalent in developing settings due to prior antibiotic use and fastidious pathogens [10,11]. Our study adds to this body of evidence by identifying asymptomatic bacteremia in clinically stable patients, emphasizing the need for better microbial detection techniques—including prolonged incubation or molecular diagnostics—especially in resource-constrained settings [12-14].

While most detected organisms were low-virulence CoNS, their presence on prosthetic valves—even in subclinical form—can serve as a nidus for future infection or embolic events. Therefore, surveillance blood cultures may be considered in certain high-risk individuals, and a high index of suspicion should be maintained even in the absence of symptoms. Prospective studies incorporating echocardiographic follow-up and molecular assays could clarify the prognostic significance of subclinical bacteremia

This study highlights a notable prevalence of subclinical bacteremia among patients with prosthetic heart valves, even in the absence of overt clinical symptoms. The identification of common low-virulence pathogens such as coagulase-negative staphylococci and Streptococcus viridans underscores the potential for silent microbial colonization of prosthetic material. Significant associations with recent valve surgery and comorbid diabetes emphasize the importance of targeted surveillance in high-risk groups. These findings suggest a need for enhanced microbiological monitoring and possibly prophylactic strategies to prevent progression to overt prosthetic valve endocarditis. Further research employing advanced diagnostics and long-term follow-up is warranted to determine the clinical significance and outcomes of subclinical bacteremia.

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