A Look at “Highly Pathogenic Organisms”

Nothing makes my skin crawl more than hearing the term “highly pathogenic organisms.” And it’s not because I’m a germaphobe. I think it’s because the term is so misunderstood. For those of you familiar with the current version of USP <797> (and hopefully that is all of you reading this), the term is used to describe microorganisms that need to be “immediately remedied” if they are recovered on viable air or surface samples, because of their risk to patient safety. The chapter went further and provided examples of the types of microorganisms that could be pathogenic. The examples were meant to be just that, examples. Unfortunately, these examples became the “bad bugs” have had a profoundly negative impact on sterile compounders’ ability to effectively operate while investigating their recovery.

So, what are “highly pathogenic organisms”? According to USP <797> (2008) they “can be potentially fatal to patients receiving CSPs.” I truly believe it was the intention of the Expert Compounding Committee responsible for the 2008 chapter that ALL recovered microorganisms needed to be evaluated for risk, otherwise why would they require identification of all growth recovered? Unfortunately, the list of examples distracted stakeholders from the concept of evaluating all recovered microorganisms and coagulase positive staphylococcus, gram negative rods, yeast, and mold became the enemies of the sterile compounding organization. This list also became the excuse to not care about anything else that was recovered.

You must remember that this is a list of very generic categories of microorganisms, except for the coagulase positive staphylococcus, which is very specific. But if you look at gram negative rods, yeast, and mold, those categories contain thousands of microorganisms, some more pathogenic/virulent than others. And the scary reality about the list in the chapter, is that it doesn’t mention spore-forming bacteria. There are some spore-forming organisms that I would be more concerned about recovering in a sterile compounding environment than those that fall into a category on the chapter’s “highly pathogenic organism” list.  

If we look at this list in its simplest form, it does provide practitioners and inspectors an easy to way to say this organism is bad and this one is not. And contract labs played into it by indicating on their reports that if you recovered one of the organisms in these four categories the sample location fails, or you have to take action, etc. But when it comes to “highly pathogenic organisms” in real life, it isn’t that black and white. In an article by Pirofski and Casadevall titled Q and A: What is a Pathogen? A Question that Begs a Point, they discuss pathogenicity. One mind blowing concept is that many think a microorganism’s ability to cause disease or even death is an inherent microbial property, when in reality this ability can only exist in a susceptible host. Immunity and the immune response play a role here. If the patient receiving a contaminated CSP is immune or is generally healthy, pathogenicity is not expressed. Simply put, pathogenicity is more due to the immune response of the patient rather than the pathogen itself. This is why you’ll hear that any microorganism can be pathogenic given the right circumstances, like route of administration, time/temperature of CSP storage, and microorganism health.

Where does this leave us? To maintain compliance with the current version of the chapter, you need to evaluate the recovery of all microorganisms and not just those on the “highly pathogenic list”. As we hopefully soon move to an updated version of USP <797>, you will only be required to identify microbial growth that exceeded the action level and the “highly pathogenic organism” list goes away. This is a definite benefit; however, a best practice recommendation is to base your identification needs on your risk. Those doing nonsterile to sterile, Category 3 compounding should have a different identification plan than those performing Category 1 compounding.

Evaluating your microbial risk can be overwhelming. Yes, looking up microorganisms online can give you an idea of the source of the contamination, but do not rely on Google to define pathogenicity for you. You want to have a multidisciplinary team in place that includes a pharmaceutical microbiologist and infection preventionists to assist you in the true risk of the recovered microorganism.

Still unsure about how to handle “highly pathogenic organisms”? Pure Microbiology provides consulting services to support you sterile compounding microbiology needs. Contact us!