Understanding pathogenesis in man : a proof of concept study

Introduction: The current understanding of the significance of circulating pathogen DNA in infection is limited. Blood cultures are the current gold standard for pathogen detection. The administration of antibiotics can confound pathogen detection by blood cultures. Polymerase chain reaction assays of circulating pathogen DNA has the potential ability for rapid diagnosis of infection and may be potentially useful in a clinical setting. However, the use of this technology has only recently been used in the study of sepsis.Animal models for the study of sepsis have added to our understanding. The failure to translate results from animals to humans has been attributed to the disease characteristics of sepsis (complexity and heterogeneity), inappropriate clinical trials (study of ineffective drugs, inadequate clinical trial designs), and animal models that do not fully mimic human sepsis. Therefore, the finding of an easily reproducible in vivo human model for pathogenaemia may provide a platform for exploring the host’s immune response to circulating pathogen material.Infection and urosepsis are common complications in diagnostic and therapeutic urological procedures. Urological interventional procedures for the removal of renal stones are commonly done in a controlled operating environment and may potentially be an in vivo model for investigating the host immune response to detected pathogen. Antibiotic prophylaxis is routinely given across the world for these urological procedures even though the evidence for their use is weak. If the presence of pathogen is seen to generate an immune response in these in vivo human models, it could be argued that there may be a potential benefit to antibiotic prophylaxis.Aim: To investigate interventional urological stone removal as a model of pathogenaemia in man and, therefore, test the following hypotheses:1. The detection of circulating pathogen DNA by SeptiFast® PCR is an indicator for the infection associated with urological procedures.2. The presence of circulating pathogen DNA correlates with the host immune and physiological response, supporting the notion that antibiotics prophylaxis is important in urological procedures.Method: In a prospective group of patients undergoing stone removal, blood samples were taken at five time points, peri-operatively to assess: The presence of pathogen by blood culture and pathogen DNA by SeptiFast® PCR; Circulating IL - 6 and IL - 10 levels to assess activation of host inflammatory response.Routine peri - operative observations were recorded throughout as measures of physiological responses.Results: Collected historical data on urological procedures by Salford Royal Foundation Trust urology services show that the SeptiFast® assay gave full coverage for pathogens seen in this clinical setting. While positive blood culture was rare, 50% of patients tested positive for pathogen DNAemia and this was associated with increased circulating IL-6 compared to patients with no circulating pathogen DNA. Linkage between pathogen DNA positivity and patient outcome was not established.Conclusion: These data provide novel evidence that pathogen DNAemia is a common feature of routine urological procedures correlating with an increased systemic8inflammatory response. Endourological stone removal interventions may be a useful model for understanding the role of pathogen DNA in triggering inflammatory responses to infection in man