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What is the larger threat of hospital-associated infection?

Updated: May 22, 2023

COVID-19 is not the pandemic I was predicting. Year after year, for just over 10 years a new class of about 150 young, smart medical students would come to my lectures on medical bacteriology and infection at Oxford. I would explain what things contribute to virulence (what makes pathogens dangerous); most years I would get them to play an online game in which a pandemic was simulated and from which they would learn some key things, with a prize for the person who could take a screen-shot of having killed the whole world population in the shortest time. The key lesson only a few learned was that infection control was the only and most effective intervention (and that the only way to get 100% death was to keep re-starting – assuming everything else was right – until the pandemic started on Madagascar, because otherwise, they would close the borders, and you could never get everyone).

When it got to teaching R0 (at a time when nobody entering the room would have previously heard of it), the discussion would move onto the factors that lower the bar for the pathogens and provide an ever-increasing risk of future new pathogen development and impacts. The factors that tip the equation in favour of the pathogens. Key amongst them are the ones that aid the spread and provide ‘learner populations’ for pathogens to develop their skills at causing disease. It is a general pattern that a pathogen can be made less dangerous by growing it in a different host (this is how the live Polio vaccine was created) and more dangerous by growing it in us (a reason why growing infectious agents from other species in human cells is foolish, or at least an inherently dangerous, thing to do). As people live in higher population densities and mix closely, such as in cities and mass-transit systems, and as the population includes more varieties of people with weakened immunity, whether from various features of old age, drug treatments for various immune-system disorders or transplants, compromising infections such as HIV, poor diets whether Western causing metabolic syndrome and diabetes or vitamin D deficiency or malnutrition associated with poverty, and many others – each of these provide new easier starting points for new pathogens to learn, develop, and cause infection with greater effectiveness. Today’s world and life is the evolutionary selective environment for tomorrow’s new and effective pathogens – and it could literally be tomorrow; it is already happening and developing today. When I told my students that they would have to face these new pathogens and pandemics in their working lives, I have been proven right already – but what I was predicting was much worse than COVID-19.

People are far more aware of zoonotic infections (infections of humans that originate in animals) than they were, but the other potential source of new pathogens: more infectable people, seems hard to find anyone addressing. It is exactly the same idea as passage in cell lines or deliberately in live animals that an organism will progressively become fitter in any environment in which it can survive and replicate. The more the world contains vulnerable people, those in which it is easier for pathogens to grow and survive, the greater the risks. To this can be added the issue of enriched environments, which is what hospitals are. Patients are not only brought together; patients with the same types of illnesses, drugs, and specific susceptibilities are brought together. There is the established example of Pseudomonas strains that transmit between patients in cystic fibrosis clinics, for example, but the reality is that there must be many more hiding amongst the other strains and emerging as future challenges.

Why does this matter? You may ask. Well, because while nosocomial infections currently cause significant harm, prolonged and complicated hospital stays, and substantial and growing numbers of deaths. A failure to contain them as they inevitably and relentlessly adapt and evolve as they are passed from person to person, one day, for sure, without question – will lead to the development of more dangerous pathogens that challenge the world beyond the hospital. We need new solutions to address this, to overcome and contain it as the considerable problem that it is today before it becomes the origin of much more serious infections and challenges tomorrow.

Dr Nigel Saunders, Chief Scientific Officer




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