Of course, there were other factors at play. For example, the patient had self-administered prednisone for some reason (an immunosuppressant) and was an extremely heavy drinker and drug user. So his immune system was most likely not functioning properly.
I'm wondering if any users here can provide insight on how often this sort of thing happens and if I should be worried about it were I to get HA.
Infections from elective procedures are an established risk. No procedure, not even modifying one's own nose isn't without risk. In the article itself it even states that facial dermal fillers have an established 1% chance of acute or delayed infection.
What needs to be understood are that the fillers in it of themselves aren't the problem, and thousands (maybe hundreds of thousands if you count Botox) of people around the world get injections daily, for a variety of reasons. What ends up happening is that you get a pathogen introduced into the body unintentionally or accidentally, and for some, it can wreak havoc.
Take a look at what I consider the most telling part of this report: "In this case, subcutaneous invasion of bacteria likely occurred during sexual intercourse through the abrasion (Fig. 1A) or a herpetic sore, which then invaded the hyaluronic acid fillers. It was considered less likely to be a delayed infection from the initial insertion of penile fillers, due to the onset of symptoms following unprotected intercourse."
The lesson here is to practice safe sex and good hygiene. This is why medical settings that perform these kinds of procedures emphasize a sterile work environment (and even then rare cases of slipups can happen). This is also why some Clinics will give you antibiotics after a procedure as a preventative measure.
The moral of the story here is that Hyaluronic Acid (HA), something naturally produced by your body, is relatively safe. Reports of complications this severe from the penile fillers we talk about here are not only rare, but almost never the fault of the filler itself. Just be mindful that if you choose to get medical work done, hell even dentistry, it isn't without risk.