This is a generic product. The brand name is by Pfizer and called SoluMedrol. SoluMedrol comes in dry form, with a diluent to add on the spot...I would think this minimizes contamination. Their system is very complex, to reconstitute as well. This generic product is premixed...and that may be a problem.

Sometimes injectables are in short supply, and compounding pharmacies can take up that slack.
If you knew how fastidious it has to be to make infusions, and injectables, you'd understand the problem. The FDA has been after compounding pharmacies for a long time, and this time it looks like something will be done. There are many home infusion places that make chemo injectables, and other things as well.
With a product like this, it could be
1) contaminated raw product (the steroid powder).
2) contaminated ampoules used to put the drug into
3) poor hood maintenance and/or air flow and filter problems
4) sloppy technique, or not following protocols.
You can be sure all will be looked at minutely now.

With epidurals there is another problem. Sometimes the doctor can nick or penetrate the dura by accident. If you search "epidurals" you find the rate of these errors. With this type of contamination, a dura puncture is very serious.

Steroids suppress the immune system giving the fungus more opportunity to become more virulent.

It is a very terrible situation, with several levels of potential
error, and blame.