Medical Device Link.

Originally Published IVD Technology September 2004

INDUSTRY NEWS

OIVD recommends that AST systems be supplemented with manual testing methods, such as the Vancomycin screen agar by BD Diagnostics (Franklin Lakes, NJ), when screening for VRSA.

Manufacturers of antimicrobial susceptibility tests (AST) must keep on their toes. Microbes continuously evolve to new and potentially drug-resistant strains, and test manufacturers must keep pace with these changes in order to keep their automated test systems up-to-date.

Recently, a third clinical isolate of vancomycin-resistant Staphylococcus aureus (VRSA) was discovered. Studies of this isolate found that IVD test systems were inconsistent in their detection of the strain, raising concerns that additional VRSA infections may occur and be missed when these systems are used for reporting S. aureus-resistance and susceptibility profiles. 

In response to these studies, the Office of In Vitro Diagnostic Device Evaluation and Safety (OIVD; Rockville, MD) warned manufacturers of AST systems of the potential shortcomings of these systems. OIVD requested that these manufacturers distribute warning labels, notify their customers of the need for additional testing, and update package inserts. Further, the office recommended that clinicians should supplement these systems with methods that have been shown to reliably detect this isolate, such as nonautomated minimum inhibitory concentration methods such as broth microdilution or agar dilution. 

What can IVD manufacturers do to stay aware of such developments and keep their AST systems up-to-date? Dade Behring (Deerfield, IL) manufactures the MicroScan overnight and rapid tests. To keep abreast of the latest developments in AST, the company participates in the NCCLS (Wayne, PA) Subcommittee on Antimicrobial Susceptibility Tests and helps to develop applicable NCCLS standards.
The company uses technical bulletins and continuing education seminars to keep its customers informed of product updates. In addition, it provides software that can be customized by users to alert them to unusual results. According to Dade Behring spokesperson Melissa Ziriakus, “It was through [software alert] processes such as these that two of the three VRSA strains were initially identified as unusual, resulting in further testing and ultimately in the identification [of the new strain] by the CDC.”

IVD manufacturers play an important role in keeping AST tests effective, according to representatives at Trek Diagnostic Systems (Cleveland) manufacturer of the Sensititre AST. “Vigilance through ongoing surveillance testing is still a necessary component. Not only industry, but also government and our customers, must continue to invest in research to push [AST] systems to higher levels of accuracy and precision,” says Les Stutzman, director of global marketing for Trek.

Representatives from BD Diagnostic Systems (Sparks, MD), manufacturer of the Phoenix AST system, agree that OIVD’s warning will ultimately benefit manufacturers. “On an ongoing basis, manufacturers need to continue challenging their systems with new, emerging resistant phenotypes. This is accomplished by supporting routine clinical evaluations as well as performing internal-challenge testing with known atypical microorganisms when available,” says John Meduri, who works in microbial identification and resistance diagnostics for BD.

Many AST manufacturers have applied to receive the strain from FDA so that they can examine how effective their systems are at detecting it. However, it may be quite some time before manufacturers can officially claim that their systems can reliably detect the new strain.

According to Meduri, “FDA has stated that manufacturers must receive 510(k) clearance to claim detection of VRSA. However, at this time, the three known VRSA strains are not sufficient [i.e., FDA has not yet identified the minimum number of strains necessary] for commercial AST systems to demonstrate their ability to detect VRSA.”

Nonetheless, FDA deems the combination of automated testing and manual backup testing to be adequate for performing VRSA testing. OIVD sent a follow-up letter to this end, informing AST manufacturers that they will not need to submit recall, correction, or removal reports for their systems.

More information on antimicrobial susceptibility testing is available from CDC’s Multilevel Antimicrobial Susceptibility Testing Educational Resources Web site at www.phppo.cdc.gov/dls/master/default.asp.  

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