Coatings & surface treatment
to keep pathogenic microbes at bay. Although there’s some evidence of infectious disease awareness in ancient and medieval history – isolating lepers in colonies and quarantining those with bubonic plague – Hungarian physician Ignaz Philipp Semmelweis was the first to highlight the role that physical touch could play in transmitting disease. His analysis, carried out in Vienna between 1840– 47 at the height of the puerperal fever epidemic is now seen as a milestone in the history of infection control. In it he drew the conclusion that the high mortality rate of 98.4 deaths per 1000 births in a maternity clinic run by medical students was caused by them conducting post-mortem examinations of women who had died of puerperal fever and then performing vaginal examinations on live patients as part of their training. By contrast, the midwives in a second maternity clinic engaged in neither activity, and had a much lower mortality rate of 36.2 deaths per 1000 births. Semmelweis theorised that the culprit was the transmission of what he called ‘decomposing animal organic matter’, and in the last year of his analysis he instituted disinfectant handwashing within both clinics. The result was a dramatic drop in the mortality rates, 12.7 deaths per 1000 births for the students, 13.3 deaths per 1000 births for the midwives. Semmelweis, of course, had no knowledge of microbes and the mechanisms through which they spread and cause disease, but his analysis laid the groundwork for innovations that help to prevent the spread of pathogens – including antimicrobial coatings.
Combatting HAIs
The development of these coatings is intertwined with the history of hospital-acquired infections (HAIs) – the name given to infectious diseases that occur due to pathogen transmission while patients are in hospital. While physicians and healthcare providers noticed patterns of infections that occurred in healthcare environments before and after the observations made by Semmelweis, it wasn’t until the late 19th century, with the advent of germ theory that the microbial causes of infectious diseases, including HAIs, began to be systematically understood. The two main contributors of germ theory were Louis Pasteur (of pasteurised milk fame) and Robert Koch. Pasteur proposed that specific microorganisms such as bacteria were responsible for causing diseases, meanwhile Koch’s postulates set out a framework for establishing a causal relationship between specific microorganisms and particular diseases, such as Mycobacterium tuberculosis and tuberculosis, Vibrio cholerae and cholera and Bacillus anthracis and anthrax. The influence of germ theory was wide reaching. Although still in their infancy, the ideas of Pasteur
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influenced the work of British surgeon Joseph Lister, who in the 1860s introduced antiseptic agents to sterilise surgical instruments. The acceptance of antiseptic techniques and hand hygiene practices in surgical and clinical settings grew slowly, prodded along by the growing body of evidence supporting germ theory, and by 1910 the mortality rate of major operations had reduced from about 40% to less than 3%. Infection caused by HAIs was seemingly being brought under control, and the 1928 discovery of penicillin by Alexander Fleming gave clinicians a weapon against disease caused by bacteria. With penicillin being so effective at treating HAIs – the majority of which were and still are caused by bacteria – it enjoyed liberal use within hospitals. But with this widespread use came a problem that still plagues clinics to this day: antibiotic-resistant bacteria. The emergence of strains of bacteria resistant to penicillin, streptomycin and several other antibiotics of the time, led to a resurgence in the importance of hand hygiene, sterilisation and disinfection, marked by earliest formal infection control programs. By the 1960s, hospital-based infection control efforts had been established in scattered hospitals throughout the US. The number of hospitals with HAI control programmes increased substantially during the 1970s, and such programmes were established in virtually every US hospital by the early 1990s. Pharmaceutical companies attempted to keep pace with the antibiotic resistance of bacteria until the early 1980s. At this point the search for new antibiotics was mostly abandoned due to the high cost of development and approval; how quickly resistance developed; and a growing awareness that the drugs had to be used sparingly – all of which meant a poor return on investment. Antimicrobial stewardship has developed to provide scientific rigour to the decision of when and when not to use certain antibiotics, through the use of antimicrobial susceptibility testing (AST). But HAIs have remained a major problem in all corners of the world. The WHO reports out of every 100 patients in acute-care hospitals today, seven in high- income countries and 15 in low- and middle-income countries will acquire at least one HAI; of these patients, one in every ten will die from their infection. There’s a recognition among the healthcare community that infection control procedures need to be maintained to avoid HAIs, but even with superbugs like methicillin-resistant Staphylococcus aureus (MRSA) or antibiotic-resistant Clostridium difficile (C.diff) remaining as common causes of infection, hand hygiene, sterilisation and disinfection procedures can vary from hospital to hospital. The Covid-19 pandemic added another reason for hospitals to stay on top of infection control procedures, but it also highlighted the role that
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