A description of the immune system taken from Wikipedia:
The immune system is a system of many biological structures and processes within us that protects against disease. To function properly, an immune system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms, and distinguish them from the organism’s own healthy tissue.
For me, my immune system is substantially weaker than most people and as such my susceptibility to infection is higher than most. When one system goes down, the rest tend to go with it.
For example, in October 2015 I got a UTI, which soon spread to be a kidney infection. It didn’t just affect my bladder though, my heart and lungs struggled more than usual which made my breathing worse, made me vomit regularly and stop eating. No amount of oral antibiotics had a big enough effect on the infection; where most people could get a prescribed antibiotic and carry on normal life.
After 4 days of IV antibiotics (antibiotics fed through a drip line) it spread into the blood stream and turned into life threatening urosepsis. My care then had to be handed over to the intensive care team.