Mycobacterium chimaera: a report of 2 new cases and literature review

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.

Mycobacterium chimaera chorioretinitis preceding central nervous system lesions: a case report and review of the literature

Background

Mycobacterium chimaera ocular infection is a rare disease that is linked to bypass devices used during cardiothoracic surgeries. Reported cases in the literature of ocular involvement preceding CNS involvement are based on clinical exam with no neuroimaging. Here we present a case of M. chimaera ocular infection with no CNS M. chimaera lesions on brain magnetic resonance imaging (MRI).

Case presentation

A 59-year-old female presented with altered mental status and blurred vision in February 2021. Her past medical history was significant for aortic valve replacement and ascending aortic aneurysm repair in 2017 complicated by known M. chimaera infection. She had been receiving azithromycin, ethambutol, rifampin, and amikacin as systemic anti-mycobacterium treatment. Her dilated fundus exam showed numerous yellow placoid circular lesions scattered throughout the macula and peripheral retina in both eyes with associated vitritis. Systemic workup, including brain MRI showed no acute infectious lesions. Her infections workup was unremarkable except for a positive toxoplasma IgM, for which she was treated with sulfamethoxazole/trimethoprim. One month later, a head computed tomography showed new numerous scattered round foci of hyperdensity throughout the cerebrum and brainstem thought to be foci of M. chimaera infection. Clofazimine was added per culture and sensitivity. MRI brain 1 month later showed mild decrease in conspicuity and number of these intensities while on anti-mycobacterium treatment. Her cognition had improved at that time as well. She was seen in retina clinic 2 months later where her exam showed similar retinal lesions with no associated vitritis or anterior chamber cell in bilateral eyes, suggesting a lack of active infection. Optical coherence tomography macula showed parafoveal cystoid macular edema bilaterally. She was started on steroidal and non-steroidal anti-inflammatory eye drops.

Conclusions

To the best of our knowledge, this is the first case in the literature to report M. chimaera chorioretinitis with concomitant negative neuroimaging. Chorioretinal M. chimaera lesions should motivate high suspicion of CNS involvement prompting early neurological work up.

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.

An Unfavorable Outcome of M. chimaera Infection in Patient with Silicosis

Mycobacterium chimaera is a slow-growing, nontuberculous mycobacterium (NTM) belonging to the Mycobacterium avium complex (MAC). It was identified as a unique species in 2004. Since 2013 it has been reported as a cause of disseminated infection in patients after cardiac surgeries. Only a few cases associated with underlying lung diseases have been noted. M. chimaera infection is characterized by ambiguous symptoms. There is no treatment with proven effectiveness, and it has a poor prognosis. Silicosis is a disease that can predispose to mycobacterial infection. Silica damages pulmonary macrophages, inhibiting their ability to kill mycobacteria. We present a case of M. chimaera infection in a patient with silicosis and without other comorbidities. To our knowledge, it is the first case of silicosis associated with M. chimaera disease. A 45-year-old man presented with a persistent low-grade fever. Based on the clinical and radiological picture, positive cultures, and histological examination, the nontuberculous mycobacterial disease was diagnosed. First, multidrug therapy according to the treatment guidelines for MAC was implemented, then antibiotics were administrated, based on drug sensitivity. Despite the treatment, eradication was not achieved and the patient died. The analysis of M. chimaera infection cases could contribute to developing recommendations and thus improve the prognosis.