Mycobacterium chimaera infections following cardiac surgery in Treviso Hospital, Italy, from 2016 to 2019: Cases report

Epidemiological and Molecular Investigation of the Heater-Cooler Unit (HCU)-Related Outbreak of Invasive Mycobacterium chimaera Infection Occurred in Italy

BACKGROUND

From 2013 onwards, a large outbreak of Mycobacterium chimaera (MC) invasive infection, which was correlated with the use of contaminated heater-cooler units (HCUs) during open chest surgery, was reported from all over the world. Here, we report the results of the epidemiological and molecular investigations conducted in Italy after the alarm raised about this epidemic event.

METHODS

MC strains isolated from patients or from HCU devices were characterized by genomic sequencing and molecular epidemiological analysis.

RESULTS

Through retrospective epidemiological analysis conducted between January 2010 and December 2022, 40 possible cases of patients infected with MC were identified. Thirty-six strains isolated from these patients were analysed by whole genome sequencing (WGS) and were found to belong to the genotypes 1.1 or 1.8, which are the genotypes correlated with the outbreak. Most of the cases presented with prosthetic valve endocarditis, vascular graft infection or disseminated infection. Among the cases found, there were 21 deaths. The same analysis was carried out on HCU devices. A total of 251 HCUs were found to be contaminated by MC; genotypes 1.1 or 1.8 were identified in 28 of those HCUs.

CONCLUSIONS

To ensure patients' safety and adequate follow-up, clinicians and general practitioners were made aware of the results and public health measures, and recommendations were issued to prevent further cases in the healthcare settings. The Italian Society of Cardiac Surgery performed a national survey to assess the incidence of HCU-related MC prosthetic infections in cardiac surgery. No cases were reported after HCU replacement or structural modification and disinfection and possibly safe allocation outside surgical rooms.

Long-Term Follow-Up after Mycobacterium Chimaera Infection Following Cardiac Surgery: Single-Center Experience

BACKGROUND

Disseminated Mycobacterium chimaera (M. chimaera) infection following cardiac surgery has been associated with a high mortality. The long-term impact of surgery and the appropriate surgical approach are still matters of debate.

METHODS

From 2015 to 2019, seven patients with M. chimaera infection following cardiac surgery were isolated.

RESULTS

The median incubation time was 30 months (IQR 18-38). Echocardiography was unremarkable in three patients (43%). We decided to redo cardiac surgery in all patients and explanted all previously implanted prosthetic material. All explant cultures yielded M. chimaera. One patient (14%) died in-hospital seven months after the redo surgery. After a median follow-up of 59.6 months (IQR 39.1-69.6), we observed three infection relapses among the survivors (43%), presumably due to concomitant extracardiac infection and recurrent cardiac implant infection.

CONCLUSIONS

M. chimaera infection following cardiac surgery is associated with a delayed and unspecific clinical presentation. Echocardiogaphy has a limited sensitivity for prosthetic valve infection with M. chimaera, and negative findings should not preclude the surgical decision. The extraction of all previously implanted material is crucial to achieving the source control, as the re-implantation of prosthetic material as well as uncontrolled extracardiac infection at the time of the redo cardiac surgery appear to be key factors for persisting/relapsing infection.

Advanced Cardiovascular Imaging for the Diagnosis of Mycobacterium chimaera Prosthetic Valve Infective Endocarditis After Open-heart Surgery: A Contemporary Systematic Review

Mycobacterium chimaera is an opportunistic and emerging pathogen, which has been recognized to cause prosthetic valve infective endocarditis and disseminated infection following open-chest cardiac surgery with certain contaminated heater-cooler systems. Diagnostic evaluation of suspected prosthetic valve infective endocarditis due to Mycobacterium chimaera is challenging and requires a very high index of suspicion. This systematic review aims to evaluate prosthetic valve infective endocarditis due to Mycobacterium chimaera. Based on the current literature review, transesophageal echocardiography and 18F-fluorodeoxyglucose positron emission tomography/computed tomography are the most common imaging modalities used to establish the diagnosis. Based on twenty-two published cases, the reported cases of Mycobacterium chimaera endocarditis have occurred almost entirely in males. Within this cohort, the patients developed endocarditis on average 2.7 years after exposure to contaminated heater-cooler systems during cardiac surgery. Mycobacterium chimaera infection is associated with significant morbidity and mortality.

Four decades of experience of prosthetic valve endocarditis reflect a high variety of diverse pathogens

Prosthetic valve endocarditis (PVE) remains a serious condition with a high mortality rate. Precise identification of the PVE-associated pathogen/s and their virulence is essential for successful therapy, and patient survival. The commonly described PVE-associated pathogens are staphylococci, streptococci and enterococci, with Staphylococcus aureus being the most frequently diagnosed species. Furthermore, multi-drug resistance pathogens are increasing in prevalence, and continue to pose new challenges mandating a personalized approach. Blood cultures in combination with echocardiography are the most common methods to diagnose PVE, often being the only indication, it exists. In many cases, the diagnostic strategy recommended in the clinical guidelines does not identify the precise microbial agent and to frequently, false negative blood cultures are reported. Despite the fact that blood culture findings are not always a good indicator of the actual PVE agent in the valve tissue, only a minority of re-operated prostheses are subjected to microbiological diagnostic evaluation. In this review, we focus on the diversity and the complete spectrum of PVE-associated bacterial, fungal and viral pathogens in blood, and prosthetic heart valve, their possible virulence potential, and their challenges in making a microbial diagnosis. We are curious to understand if the unacceptable high mortality of PVE is associated with the high number of negative microbial findings in connection with a possible PVE. Herein, we discuss the possibilities and limits of the diagnostic methods conventionally used and make recommendations for enhanced pathogen identification. We also show possible virulence factors of the most common PVE-associated pathogens and their clinical effects. Based on blood culture, molecular biological diagnostics, and specific valve examination, better derivations for the antibiotic therapy as well as possible preventive intervention can be established in the future.

Mycobacterium chimaera Outbreak Management and Outcomes at a Large Pediatric Cardiac Surgery Center

BACKGROUND

In 2012, a global outbreak of invasive Mycobacterium chimaera (M. chimaera) infection was identified in patients post-cardiopulmonary bypass (CPB) surgery. Investigations revealed the source to be heater-cooler unit (HCU) exhaust, with point-source contamination discovered at the LivaNova HCU manufacturing plant. We report our experience with affected HCUs at a high-volume pediatric cardiac surgery center in the United States.

METHODS

A multi-disciplinary task force was established for outbreak management, including removing contaminated HCUs from service. Patients identified as exposed to affected HCUs were systematically contacted. A call center was created for patient/family inquiries, and symptomatic patients were assessed using an institutional triage protocol, including lab/culture data and infectious diseases consultation.

RESULTS

CPB surgeries were performed in 4,276 patients (median age 2.1 years, range 0-48.4) between October 2010 and October 2016. Call center volume was highest in the first 6 weeks following patient notification, totaling 307 calls and yielding 70 clinical patient assessments. Presenting symptoms included fatigue (60%), fever (49%), night sweats (46%), myalgias (34%), and weight loss (24%). Among the 70 assessed patients, echocardiogram (n=30), cardiac CT (n=2), cardiac MRI (n=1), and pulmonary CT (n=1) did not reveal abnormalities suggestive of active infection. Infectious diseases consultation occurred in 23 (33%) patients. Acid fast bacilli blood cultures were obtained in 30 patients; all were negative.

CONCLUSIONS

Through a highly coordinated outreach effort, no patients have been found to have M. chimaera infection in the six years after exposure to contaminated HCUs. Ongoing vigilance for cases that may yet manifest is needed.

Longest incubation period of Mycobacterium chimaera infection after cardiac surgery

Mycobacterium chimaera infections have been associated with contamination of a heater-cooler unit used during cardiopulmonary bypass procedures since 2006. Mycobacterium chimaera is a slow-growing non-tuberculous mycobacterium responsible for an infection, which is difficult to treat and has often a devastating course. Until now, M. chimaera infection has been shown to occur up to 8 years after operation. We report a patient presenting with an aortic pseudoaneurysm who developed M. chimaera infection 12 years after repair of an acute type A aortic dissection with graft replacement of the ascending aorta and stent-grafting of the arch. As far as we know, this is the case with the longest incubation period of M. chimaera infection. The present experience indicates that all patients who underwent open heart procedures since 2006 with such heater-cooler unit model should be closely followed up regardless of time of index surgery.