Presence of atherosclerosis risk factors and inflammation can help predict life-threatening vascular infection associated with non-typhoidal Salmonella bacteremia
Non-typhoidal Salmonella (NTS)—a foodborne bacterium causing gastrointestinal infections—is also known to cause life threatening vascular infections, possibly by invading the damaged aortic vessels in patients with atherosclerosis. Providing evidence in this regard, researchers from NCKU, Taiwan found higher aortic calcification and elevated plasma levels of IL-1β—an inflammatory biomarker—in patients with NTS vascular infection. Their findings suggest the need for early diagnosis of this condition in patients with atherosclerosis risk factors.
Although foodborne bacteria are a common occurrence, some of them can cause serious and life-threatening infections. Non-typhoidal Salmonella (NTS) is one such bacterium, known to cause vascular infections (NTS vascular infections) with serious consequences. According to studies, such vascular infections develop in approximately 9%–40% of patients aged ≥50 years with NTS bacteremia. Clinical evidence points to the occurrence of vascular infection due to bacterial seeding in the damaged atherosclerotic aorta (fat and calcium plaque built-up in large blood vessel) of patients with NTS bacteremia, suggesting atherosclerosis to be a risk factor for developing infection. However, this association of NTS vascular infection and atherosclerosis lacks evidential support from rigorous clinical studies.
To address this gap, a group of researchers from Taiwan led by Dr. Po-Lin Chen, in the Department of Internal Medicine, National Cheng Kung University (NCKU) Hospital, conducted a prospective study to examine this association further. Talking about the study, Prof. Chen says, “We attempted to evaluate the risk of NTS vascular infection with atherosclerosis by examining aortic calcification and serum levels of inflammatory biomarkers in patients with NTS bacteremia. We also tested the validity of the NTS vascular infection score proposed in our previous research for determining infection risk.” This study was made available online on 21 June 2022, and subsequently published in Volume 55, Issue 3 of the Journal of Microbiology, Immunology and Infection.
In this study, 69 patients with NTS bacteremia (mostly comprising males aged ≥50 years) underwent abdominal and/or thoracic CT scan to detect vascular infection. Atherosclerosis severity was measured by obtaining the aortic calcium scores from unenhanced CT calcium scanning.
The NTS vascular infection score (NTSVI) proposed by Prof. Chen and his colleagues in a previous study was calculated based on four risk factors, of which hypertension and coronary artery disease are directly linked to atherosclerosis. Blood plasma levels of important inflammatory markers were also analyzed for this investigation.
The researchers found that calcium scores were higher in patients with NTS vascular infection when compared with those without the infection. As for the NTSVI score, none of the patients with a score less than 1 reported vascular infection. Rather, the prevalence of infection was found to increase with increasing score, validating the score’s predictive ability.
Of the five biomarkers assayed using blood plasma samples, higher concentrations were detected only for interleukin 1 beta (IL-1β)¬–an inflammatory cytokine protein, in patients with vascular infection when compared with those without infection.
Discussing the results, Prof. Chen says, “Higher calcium scores in patients with NTS vascular infection indicates that the risk of developing vascular infections is high with atherosclerotic severity. The NTSVI score, which also determines atherosclerotic severity, can be used with ease in clinical settings to categorize patients based on the risk of vascular infection.”
Moreover, this research also supports the hypothesis about the pivotal role IL-1β plays in Salmonella infections, as suggested by previous studies. Plasma levels of IL-1β among patients with NTS bacteremia have significant clinical relevance as a potential biomarker as well as a therapeutic target among high-risk patients.
Explaining the real-life applications of these results, Prof. Chen says, “With an overall increase in aging and atherosclerosis, susceptibility to NTS vascular infections also increases. Moreover, the mortality rate associated with delayed diagnosis is high. In such a situation, if a patient with NTS bacteremia is found to have risk factors of atherosclerosis, aggressive examination using a comprehensive CT scan for diagnosing coexisting NTS vascular infection is recommended.”
Though further rigorous and exhaustive studies are required to validate the use of NTSVI score and IL-1β as an inflammatory biomarker, this study has set the ball rolling for early detection and appropriate remediation of this life-threatening infection.
