FDA Cautions in Interpretation of Antimicrobial Resistance Data
April 22, 2013
Recently, the Environmental Working Group issued a report of its interpretation of the 2011 Retail Meat Annual Report of the National Antimicrobial Resistance Monitoring System (NARMS). While FDA is always concerned when we see antimicrobial resistance, we believe the EWG report oversimplifies the NARMS data and provides misleading conclusions. We do not believe that EWG fully considered important factors that put these results in context, including:
- whether the bacterium is a foodborne pathogen. The report highlights resistance to Enterococcus, but this is not considered a major foodborne pathogen. Instead, we include it because its behavior is helpful in understanding how resistance occurs.
- which drug(s) the bacterium is naturally resistant to. For example, most Enterococcus faecalis is naturally resistant to the antibiotic class of lincosamides. Because we know and expect to see this resistance, we are not as concerned with resistance in this species the way we would be with resistance in true pathogens like Salmonella and Campylobacter.
- why NARMS includes certain drugs in its testing design. We include some antibiotics for epidemiology purposes-- to track the spread of certain bacteria or certain genes. But resistance to these antibiotics doesn’t reflect a danger to public health.
- whether the antibiotics that are commonly used to treat patients are still effective. NARMS data indicates that first-line treatments for all four bacteria that we track (Salmonella, Enterococcus, Escherichia coli and Campylobacter) are still effective.
- what the 2011 data indicate relative to similar data reported for prior years.
Additionally, we believe that it is inaccurate and alarmist to define bacteria resistant to one, or even a few, antimicrobials as “superbugs” if these same bacteria are still treatable by other commonly used antibiotics. This is especially misleading when speaking of bacteria that do not cause foodborne disease and have natural resistances, such as Enterococcus.
When taking such factors into account, FDA believes the notable findings in the 2011 NARMS Report include:
- In the critically important class of antimicrobials, the 2011 data showed no fluoroquinolone resistance in Salmonella from any source. This is the drug of choice for treating adults with Salmonella.
- Trimethoprim-sulfonamide is another drug used to treat Salmonella infections and resistance remains low (0% to 3.7%).
- Fluoroquinolone resistance in Campylobacter has stopped increasing and remained essentially unchanged since the FDA withdrew the use of this drug class in poultry in 2005.
- Macrolide antibiotic resistance in retail chicken isolates remains low, with 2011 results at 0.5% of Campylobacter jejuni and 4.3% of Campylobacter coli. The macrolide antibiotic erythromycin is the drug of choice for treating Campylobacter infections.
- Multidrug resistance is rare in Campylobacter. Only nine out of 634 Campylobacter isolates from poultry were resistant to 3 or more antimicrobial classes in 2011. However, gentamicin resistance in Campylobacter coli markedly increased from 0.7% in 2007 (when it first appeared in the NARMS retail meat report) to 18.1% in 2011. Gentamicin has been suggested as a possible second-line therapy for Campylobacter infections, although it is not commonly used.
- Resistance to third-generation cephalosporins, which are used to treat salmonellosis, has increased in Salmonella from chicken (10 to 33.5%) and turkey (8.1 to 22.4%) meats when comparing 2002 and 2011 percentages. FDA noted this development in previous years and has already taken action by prohibiting certain extra-label uses of cephalosporins in cows, pigs, chickens and turkeys, and is continuing to closely monitor resistance to these drugs.
Antimicrobial resistance is a serious and challenging issue. It is critically important that we continue our efforts to minimize antimicrobial resistance, including promoting appropriate and judicious use of antimicrobials in both humans and animals.
Based on a thorough review of the available scientific information, FDA has created a strategy for the judicious use of medically important antimicrobials in food-producing animals that states their use should be limited to situations where the drugs are necessary for ensuring animal health, and done so under veterinary guidance. It is the non-judicious use – for growth promotion and feed efficiency – that is of particular concern to FDA. This collaborative strategy is intended to provide the quickest way to achieve the greatest degree of public health protection, but it does not prevent FDA from initiating regulatory action in the future, if the agency finds it necessary. FDA welcomes all contributions in helping to understand and address the challenge of antibiotic resistance. However, it is very important to look at the NARMS data in the proper context, with a good understanding of the microbiology, epidemiology and genetics of antibiotic-resistant foodborne pathogens and their clinical management.