Updated Experience of Mycobacterium chimaera Infection: Diagnosis and Management in a Tertiary Care Center

Radiologic Manifestations of Mycobacterium chimaera Infection After Open Heart Surgery

PURPOSE

The objective of this study is to identify and detail the radiologic manifestations of surgical site and disseminated Mycobacterium chimaera ( MC) infection. The aim is to facilitate early identification and diagnosis of MC, considering its indolent nature and the challenges involved in clinically and pathologically establishing the diagnosis.

PATIENTS AND METHODS

This was a retrospective cohort study reviewing computed tomography (CT), positron emission tomography (PET)/CT, and magnetic resonance imaging examinations in patients over the age of 18 years with a history of open heart surgery and a clinical or pathologic diagnosis of MC. Two radiology residents, a fellowship-trained nuclear medicine radiologist, and a fellowship-trained cardiothoracic radiologist performed consensus reads to determine the imaging findings seen in MC infection.

RESULTS

Twenty-five patients were included. Localized, surgical site infection was more common than disseminated disease. Typical CT findings included peristernal soft tissue thickening, sinus tracts often extending to the cutaneous surface, slowly enlarging fluid collections, and sternal osteolysis. PET/CT findings demonstrated hypermetabolic activity in nearly all patients localized to sites of infection. Imaging findings for disseminated infection included hepatosplenomegaly, lymphadenopathy, involvement of the central nervous system, discitis/osteomyelitis, and distant abscesses.

CONCLUSIONS

Imaging plays a vital role in suggesting possible surgical sites and disseminated MC infection acquired from open heart surgery. Radiologists must keep a high index of suspicion given the indolent nature and subtle imaging change over time. PET/CT is most useful in diagnosis and helps in differentiating between a sterile postoperative fluid collection or scarring and active MC infection and helps provide a target for debridement.

Multimodal Imaging in Mycobacterium Chimaera Cardiovascular Infections: The Mayo Clinic Experience

Objective

To review the salient features of multimodality cardiovascular imaging in patients with disseminated Mycobacterium chimaera (MC) infections after exposure to contaminated heater-cooler units during cardiopulmonary bypass.

Patients and Methods

Twelve patients with confirmed MC infection were retrospectively identified after a review from January 1, 2010, to April 30, 2021. The electronic medical records were examined with a focus on transthoracic echocardiography, transesophageal echocardiography, cardiac computed tomography (CT), cardiac magnetic resonance imaging, and positron emission tomography-CT.

Results

Three (27.3%) patients had diagnostic findings of endocarditis on transthoracic echocardiography, with most patients having nonspecific abnormalities including elevated prosthetic valve gradients or prosthetic leaflet thickening. Transesophageal echocardiography identified 4 (36.7%) patients with vegetations and 3 (27.3%) with aortic root abscess or pseudoaneurysm, with more common findings such as mild aortic root or prosthetic leaflet thickening. Six (50%) patients underwent cardiac CT imaging, which found aortic root pseudoaneurysms or abscesses, prosthetic ring dehiscence, and leaflet thickening. Three (25%) patients underwent cardiac magnetic resonance imaging demonstrating prosthetic valve vegetations, leaflet thickening, and abnormal myocardial delayed enhancement in a noncoronary distribution, suggesting myocarditis. Ten (83%) patients underwent positron emission tomography-CT, 4 (40%) had an abnormal fluorodeoxyglucose uptake around the cardiac prosthetic material, and 7 (70%) had a fluorodeoxyglucose uptake in other organs, suggesting concomitant multiorgan involvement.

Conclusion

Multimodality cardiovascular imaging is central to the management of patients with disseminated MC and can help establish a preliminary diagnosis while awaiting confirmatory microbiological data, potentially reducing the time to diagnosis. Imaging findings are subtle and atypical, not always meeting classically modified Duke's criteria for infectious endocarditis. Clinicians should have a high index of suspicion for the disease and a low threshold for repeat imaging when initial testing is equivocal.

Detection of Mpox Virus Using Microbial Cell-Free DNA: The Potential of Pathogen-Agnostic Sequencing for Rapid Identification of Emerging Pathogens

BACKGROUND

The 2022 global outbreak of Monkeypox virus (MPXV) highlighted challenges with polymerase chain reaction detection as divergent strains emerged and atypical presentations limited the applicability of swab sampling. Recommended testing in the United States requires a swab of lesions, which arise late in infection and may be unrecognized. We present MPXV detections using plasma microbial cell-free DNA (mcfDNA) sequencing.

METHODS

Fifteen plasma samples from 12 case-patients were characterized through mcfDNA sequencing. Assay performance was confirmed through in silico inclusivity and exclusivity assessments. MPXV isolates were genotyped using mcfDNA, and phylodynamic information was imputed using publicly available sequences.

RESULTS

MPXV mcfDNA was detected in 12 case-patients. Mpox was not suspected in 5, with 1 having documented resolution of mpox >6 months previously. Six had moderate to severe mpox, supported by high MPXV mcfDNA concentrations; 4 died. In 7 case-patients, mcfDNA sequencing detected coinfections. Genotyping by mcfDNA sequencing identified 22 MPXV mutations at 10 genomic loci in 9 case-patients. Consistent with variation observed in the 2022 outbreak, 21 of 22 variants were G > A/C > T. Phylogenetic analyses imputed isolates to sublineages arising at different time points and from different geographic locations.

CONCLUSIONS

We demonstrate the potential of plasma mcfDNA sequencing to detect, quantify, and, for acute infections with high sequencing coverage, subtype MPXV using a single noninvasive test. Sequencing plasma mcfDNA may augment existing mpox testing in vulnerable patient populations or in patients with atypical symptoms or unrecognized mpox. Strain type information may supplement disease surveillance and facilitate tracking emerging pathogens.

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.

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.

Disseminated Mycobacterium chimaera infection in a patient with adult-onset immunodeficiency syndrome: case report

BACKGROUND

Patients with adult-onset immunodeficiency syndrome due to anti-interferon-γ autoantibodies (AIGAs) are susceptible to disseminated Mycobacterium avium complex (MAC) infections. M. chimaera, a newly identified MAC species, is distinguished from the others due to the reduced virulence. Previous cases of disseminated M. chimaera infection have been linked to cardiothoracic surgery. Reports of disseminated M. chimaera in patients without a history of cardiothoracic surgery are rare.

CASE PRESENTATION

A 57-year-old Asian man, previously healthy, presented with fever, dry cough, exertional dyspnea, and decreased appetite. The delayed resolution of pneumonia despite antibiotic treatment prompted further imaging studies and biopsies from the lung and lymph node. The fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) demonstrated intense uptake in lung consolidations and diffuse lymphadenopathy. Cultures of the specimens obtained from sputum, blood, stool, lung tissue, and lymph node grew M. chimaera. Further immunological evaluation disclosed the presence of neutralizing AIGAs, which possibly led to acquired immunodeficiency and disseminated M. chimaera infection.

CONCLUSIONS

We herein present the first case of adult-onset immunodeficiency due to AIGAs complicated with disseminated M. chimaera infection. Further immunological evaluation, including AIGAs, may be warranted in otherwise healthy patients who present with disseminated mycobacterial infection.

Pharmacologic management of Mycobacterium chimaera Infections: A Primer for Clinicians

Mycobacterium chimaera, a member of the Mycobacterium avium complex, can cause infections in individuals after open heart surgery due to contaminated heater-cooler units. The diagnosis can be challenging, as the incubation period can be quite variable, and symptoms are nonspecific. In addition to aggressive surgical management, combination pharmacologic therapy is the cornerstone of therapy, which should consist of a macrolide, a rifamycin, ethambutol, and amikacin. Multiple second-line agents may be utilized in the setting of intolerances or toxicities. In vitro susceptibility of these agents is similar to activity against other species in the Mycobacterium avium complex. Drug–drug interactions are frequently encountered, as many individuals have chronic medical comorbidities and are prescribed medications that interact with the first-line agents used to treat M. chimaera. Recognition of these drug–drug interactions and appropriate management are essential for optimizing treatment outcomes.