Vaishnavi Kardale, Bioinformatics Centre, Savitribai Phule Pune University
Over the coming decade, the world population over the age of 60 is expected to increase steadily. Human life expectancy has increased dramatically over the last two centuries owing to the development of modern medicine, vaccination, and surgeries. Surgeries performed under the effect of anesthesia have saved countless lives. However, what if the life-saving procedures the very opposite of what they are supposed to do?
Cardiothoracic surgeries are some of the most complicated and delicate procedures performed. Some procedures like open-heart surgeries require the heart to be stopped completely for the surgeon to work upon. Under such circumstances, the heart-lung machine is connected to the patient. It is this machine that performs the work of the heart and the lungs while the patient is being operated on.
More on the heart-lung machine:
The heart-lung machine exchanges the carbon dioxide with oxygen and cleanses it. It also removes air from the aorta before the heart is made functional again. The Heater-Cooler is an important component of the heart-lung machine. This system is responsible for cooling down the body of the patient. This is required to slow down metabolism throughout the surgical procedure. Once that is done it brings back the temperature to normal. The temperature control is done with the help of water. But water has another quality that we must mention here: water is an excellent resource to breed a variety of bacteria.
What is wrong with the water in the heater-cooler?
Common water contaminants like Mycobacterium avium, Mycobacterium chimaera, and other non-tuberculous mycobacteria (NTM) can be present in the functional component of the heart-lung machine. These opportunistic pathogens cause respiratory illness among immunocompromised patients. In 2013 two patients with prior cardiac surgery were diagnosed with M. chimera infection.
The contaminated water in the heater-cooler machine can sometimes generate aerosols that reach the operational field during surgery, settling on operational situs and implants, thereby causing infections among patients.
A new research:
Schreiber et al. observed that all infections among patients of cardiac surgery were associated with exposure to the heater-cooler device (HCD) of a company called LivaNova in London. In 2016 a study by Haller S et al. was able to grow M. chimera from the samples derived from water at the LivaNova plant. When water samples from HCD of other manufacturers were taken they also grew M. chimera however they did not cause any cardiac surgery-associated infection. To study these findings, the researchers performed a whole genome sequencing (WGS) analysis.
Contamination of machines before shipping:
A high level of genetic similarity was found between the samples taken from the LivaNova production site and cardiac patients that reported infection. This suggested that the LivaNova machine became contaminated with M.chimera during production before they were shipped to hospitals.
The samples taken at the LivaNova production site were sub-grouped into three (1.1, 1.8, and 1.3). Of these three, only subgroup 1.1 was found in diseased open-heart surgery patients. An explanation for this phenomenon is not yet known. However, strain-specific properties like the capacity to replicate, higher virulence, and higher propensity for aerosolization might be responsible for this observation. One patient also got HCD contamination from the hospital.
In conclusion, the genomic analysis suggests that the predominant source of M.chimera infection in cardiac surgery patients is due to contamination at the LivaNova manufacturing site. However, local contamination from a hospital is also possible according to the whole genome sequencing analysis.
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Reference:
- Schreiber, P. W., Kohl, T. A., Kuster, S. P., Niemann, S., & Sax, H. (2021). The global outbreak of Mycobacterium chimaera infections in cardiac surgery – A systematic review of whole genome sequencing studies and joint analysis. Clinical Microbiology and Infection. Published. https://doi.org/10.1016/j.cmi.2021.07.017
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Author info:
Vaishnavi Kardale is a master’s student at the Bioinformatics Centre, Savitribai Phule University. She is interested in protein folding mechanisms and wants to study them further.
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