Immune reconstitution inflammatory syndrome is a rare condition where the presence of an infection, or even the presence of a past infection, causes an overwhelming inflammatory response in a patient whose immune system has been compromised and has been allowed to recover. It can happen when a patient recovers from a condition such as radiation sickness or stops using immunosuppressants such as steroids.
In most cases, it is preferable to let the illness run its course as it will often help to fight off the underlying illness. Steroids are contraindicated as they can cause severe immunosuppression and allow the infection to run unabated.