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From: Food Quality & Safety magazine, April/May 2007

Validating Microbiology

Proficiency Test Standards Aim to Improve Lab Safety, Reduce Public Health Risk and Increase Material Consistency

by Joe Perrone

The H2N2 virus of the late 1950s was fully transmissible among humans. It circulated in humans and caused annual epidemics until 1968, when it vanished after the emergence of influenza A/H3N2 viruses that caused the next pandemic.

A subsequent investigation of the H2N2 strain identified in the lab by Canada’s National Public Health Agency traced the virus to a microbiology proficiency test panel that was sent to the lab as part of routine distribution of blinded samples for testing. At the time the virus was identified, nearly 4,000 panels containing the same H2N2 strain had been shipped to laboratories in the U.S. and Canada, as well as to 61 labs in 16 other countries.

The World Health Organization (WHO) and the U.S. Department of Health and Human Services (DHHS) requested that all samples containing the H2N2 virus be destroyed and the destruction confirmed. No H2N2-related illness was reported in any of the labs where the proficiency panels were sent. But the potential for significant negative public health implications of an infection by the virus was present given that anyone born after 1968 will mostly likely have little or no immunity to H2N2.

The event caused DHHS and the Centers for Disease Control and Prevention (CDC) to analyze the events that led to the inclusion of H2N2 in the proficiency test panels. A complex interplay between existing conditions and specific actions led to the inclusion of the H2N2 virus in the panels (Figure 1). Among the causal factors for the H2N2’s presence in the panel was that labeling and documentation practices for stored influenza isolates did not facilitate easy recognition of isolate strain characteristics. A CDC investigation also revealed that the epidemiologic importance of switching to an H2N2 strain was not considered a major factor, as test providers or manufacturers chose agents for the proficiency test panels. One of the findings from the CDC investigation was that laboratory personnel are not properly informed about the microbes they handle in proficiency panels.

HHS asked American Type Culture Collection (ATCC; Manassas, VA) to develop measures to prevent a similar occurrence in the future. In response, ATCC developed the Proficiency Testing Standards Program to provide authenticated bioreagents for use in the manufacture of laboratory proficiency test panels. The ATCC program offers standard starting materials for proficiency testing panels to service providers and manufacturers to order under a license agreement.

The program operates on an annual cycle as follows: First, proficiency test manufacturers must provide details on the strains or materials to be included in the test panels. The goal is twofold: the manufacturers to communicate what materials they are seeking for the panels and for the ATCC to verify that the materials are in compliance with relevant safety regulations. The second component of the program is production, authentication and characterization by ATCC scientists of the biomaterials to be used in the test panels. Finally, the materials are serially labeled as proficiency test standards and are designated for sole use in test panels.

Current Challenges

Microbiology proficiency testing in clinical laboratories allows ongoing evaluation of performance and improves the accuracy of results. However, the public health risks posed by the inclusion of the H2N2 virus in proficiency panels illustrates only one of the several current challenges that prevent optimal performance of the proficiency testing system.

Several additional challenges arise at various points in the proficiency manufacturing and distribution process. Decision-making about which strains will be included in a panel is problematic because a formalized process does not exist. Strain choices for the test panels are often not vetted for consideration of possible public health implications, which can potentially expose laboratory workers to unnecessary public health risks. Manufacturers largely make decisions, so proficiency test providers are not always aware of exactly what organisms in the panel are sold. Difficulties associated with a lack of defined processes and criteria for selection generate labeling and documentation issues for stored isolates, which often lack information about strain identity, characteristics and safety.

Other challenges revolve around how microorganisms that are intended for test panels are handled and stored. Significant variations exist among manufacturers. Those variations can influence microbe handling and storage, giving rise to possible differences in microorganism properties and characteristics.

Inconsistency also exists with regard to shipping and traceability of the test panel microbes. Further, microorganisms contained in test panels generally are not tested and characterized, eliminating assurances of the cultures’ identity and purity. Because cultures are retained for use in test panels manufactured over multiple years, excessive sub-culturing of microorganisms is possible. This can also contribute to variation and inconsistency in the genotypic and phenotypic characteristics of the microorganisms in the test panels, which confounds efforts to compare test results from year to year.

Incorrectly identified, contaminated, or inconsistent proficiency test materials can affect on test evaluation. Laboratories undertaking proficiency tests are often judged to pass or fail based on their conformity to the majority of responding laboratories rather than on the accuracy of their results.

Aside from reducing the public health risks posed by the proficiency test samples, perhaps the paramount issue facing the clinical laboratory proficiency testing system is improving the validity of the assessment. Stable, well-characterized reference materials are prerequisites for valid quality assessment in clinical labs. Authenticated standard reference microorganisms bring consistency to the tests and allow results to be meaningfully compared among a group of laboratories. These features are absent if such reference material is not available for the panels and clinical isolates are used instead.

Future Improvements

Proficiency test standards will address these challenges and improve lab safety, reduce public health risk, and increase the consistency of the materials. A standards program for proficiency testing will also help increase validity in microbiology proficiency testing programs by ensuring the use of authenticated organisms in test panels.

Implementing such a program would reduce liability for proficiency testing manufacturers, providers and laboratory directors and increase safety for lab workers. The microbiology proficiency testing system benefits by taking advantage of the expertise in handling, storing, authenticating, and distributing microorganisms offered by a biological resource center like ATCC. Specifically, the a proficiency testing standards program aims to improve the current situation in a number of ways:

  • By providing dedicated proficiency testing stocks that are lot- and vial-traceable, accompanied by a detailed certificate of analysis, the chain-of-custody for the microorganisms in proficiency testing panels is established and documented;
  • To improve year-to-year consistency, manufacturers will receive fresh strains each year and destroy remaining material when panel assembly is complete;
  • Proficiency test standard microorganisms will be provided in vials labeled with serial numbers to allow traceability to the level of individual vials;
  • Proficiency test standards intended for PT manufacturers will be lot-specific and will be assigned unique catalog numbers.

Joe Perrone is vice president of standards and certification, American type, for ATCC (Manassas, Va.). Reach him by contacting Scott Jenkins, ATCC’s director of communications, at 703-365-2879.

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