USP < 797 > Viable Air and Surface Sample Reports: 3 common errors

The revision to USP <797> that became official on November 1, 2023, brought more frequent viable surface sampling requirements that affected all sterile compounders. However, those who compound Category 1 and Category 2 sterile preparations are still only required to collect viable air samples in the classified environments every 6 months.

With this infrequent collection, many locations are outsourcing this sample collection to a certification company who, in turn, outsources the incubation and analysis to a contract microbiology laboratory. 

The report generated by the contract microbiology laboratory is highly anticipated because it provides insight into the microbial state of control of the sterile compounding area. Unfortunately, much of the report is skimmed over, especially if all sample counts were below action levels. Errors in testing and reporting are not uncommon, and it is critical for sterile compounders to know what to look for on their viable sampling reports.

Error 1 – Identifications not done to the genus level

USP <797> requires that any viable air or surface sample that exceeds the established action level has all recovered microorganisms identified to the genus level. It is critical that individuals reviewing viable sampling reports understand the difference between a microbial identification and microbial characterisation.

USP <1113> Microbial Characterization, Identification, and Strain Typing defines this difference:

Microbial identification: “The determination of which broad group (e.g., bacteria, yeast, or mold) or narrow group (e.g., genus and/or species) to which a laboratory isolate belongs.”

Microbial characterisation: “The use of colony growth, cellular morphology, differential staining, and key diagnostic features to characterize a laboratory isolate for trending and investigative purposes without identification, e.g., nonpathogenic Staphylococci.”

Notice the difference between these definitions. A microbial identification includes narrowing the microorganism down to the genus and species level, while characterisation does not provide this information. It is critical to review laboratory reports to ensure the laboratory is providing identifications and not simply characterising the recovered colonies.

Notice the difference between these definitions

If the report only contains Gram stain results such as “gram positive cocci” or “gram negative,” this should prompt a discussion with the laboratory, as these are not identifications to the species level and do not meet USP <797> requirements. 

There may be situations where the laboratory cannot attain an identification because a microorganism is no longer viable or cannot be identified on the identification system. This is acceptable according to USP <797> so long as the laboratory attempted to get an identification. 

Error 2 – Incubation parameters are not clear

USP <797> defines incubation parameters for single plate viable air and surface samples. The chapter requires trypticase soy agar (TSA) samples to be incubated at 30 to 35°C for at least 48 hours and then transferred to 20 to 25 °C for at least 5 days.

A common error noted on laboratory reports is that the first incubation is two days. It is not acceptable to report that the first incubation was done for two days. Two days is not necessarily equivalent to 48 hours.

Look for indications on the laboratory report of a two-day incubation period

For example, if a laboratory places samples in the incubator on Monday at 4pm and removes them for analysis on Wednesday at 9am, this does not meet chapter requirements. Yes, the samples were incubated for two days, but they were not incubated for 48 hours.

Additionally, USP <1117> Microbiological Best Laboratory Practices specifics that any analysis that is less than 72 hours is to be reported in hours, while analysis that is greater than 72 hours can be reported in days.

Look for indications on the laboratory report of a two-day incubation period. If it is not clear what was done from looking at the report, request a copy of their standard operating procedure (SOP). If they are unwilling to share their SOP, consider auditing their operation. 

Error 3 – Total microbial count reported as 0 Colony Forming Units

With sterile compounding facilities, many samples will result in 0 Colony Forming Units (CFU). Even though there were no colonies recovered, from a microbiological reporting standpoint, the level of detection is 1 CFU. Therefore, samples with 0 CFU are to be reported as <1, with the appropriate units. CFU/m3 is used for viable air samples and CFU/plate is used for contact plates. The reporting of USP <797> viable samples is defined in the Controlled Environment Testing Association’s (CETA) Application Guide (CAG)-009 titled Viable Environmental Monitoring for Sterile Compounding Facilities.

In closing, many times the certification reports get reviewed thoroughly, while the data in the viable sampling report gets skimmed through. Take the time to review the viable air and surface report. Ensure the laboratory is actually providing identifications, the incubation parameters are clear, and the results are properly reported. 

References

1. United States Pharmacopeial Convention, Inc. General Chapter <797> Pharmaceutical Compounding—Sterile Preparations. 2023.
2. United States Pharmacopeial Convention, Inc. General Chapter <1113> Microbial Characterization, Identification, and Strain Typing. 2022.
3. United States Pharmacopeial Convention, Inc. General Chapter <1117> Microbiological Best Laboratory Practices. 2022.
4. Controlled Environment Testing Association. CAG-009 Viable Environmental Monitoring for Sterile Compounding Facilities. September 2020.