Drug-resistant E. coli in Women with Acute Cystitis in Canada
Abstract & Commentary
By Joseph F. John, JR, MD, MD, FACP, FIDSA, FSHEA
Associate Chief of Staff for Education, Ralph H. Johnson Veterans Administration Medical Center; Professor of Medicine, Medical University of South Carolina, Charleston, Co-Editor of Infectious Disease Alert.
Dr. John reports no financial relationships in this field of study
SYNOPSIS: 330 family physicians assessed 752 women with suspected acute cystitis between 2009 and 2011 in Canada. Physicians documented clinical features and collected urine for cultures for 430 (57.2%) women. The proportion of TMP-SMX-resistant Escherichia coli was 16.0% nationally.
SOURCE: McIsaac WJ, et al. Antibiotic-resistant Escherichia coli in women with acute cystitis in Canada. Can J Infect Dis Med Microbiol 2013;24:143-149.
Canada is a bit like middle America. It is not that the entire landscape escapes metropolis. Yet Canada is a land of vast spaces and smaller towns and cities, like much of America still. So this article about 330 family practices across Canada provides information about a broad middle class. From 2009 through 2011 there were 14,576 family physicians eligible to enroll. Only 4.5% did so but these practices provided 430 cultures from women with a diagnosis of acute cystitis. When complete information on the women was analyzed, 91.4% of the women had acute cystitis; 31% had received antibiotics in the previous 3 months. In 61.2% of women, urine cultures were positive. Escherichia coli was by far the most common pathogen (79.1%). Staphylococcus saprophyticus and Enterococcus species caused 2.3% and 1.9% of cystitis respectively.
The prevalence of antibiotic resistance was the feature of the study. Nationwide, TMP-SMX resistance was 16% compared to only 10.9% back in 2002. Ciprofloxacin resistance jumped from 1.1% in 2002 to 5.5% in the current study. There were regional variations. For example in British Columbia there was a 17.7% resistance to ciprofloxacin compared to only 2.7% nationally. TMP-SMX resistance was higher in premenopausal women than older women. The percentage of resistance to ampicillin, TMP-SMX, or ciprofloxacin did not change statistically over the 3 years of the study. In the entire study only one isolate, an E. coli, produced an extended spectrum beta-lactamase.
Physicians will respond to thresholds, particularly with regard to the use of antimicrobials. When resistance rates hits a certain threshold—and these thresholds may not always be well established—physicians will alter their prescribing patterns. The question of how high a rate of antimicrobial resistance is necessary to alter prescribing preferences is not easy to answer. From my experience a threshold like 20% seems a maximum level that will change perceptions. What may be a minimal rate is a harder question to answer, but physicians become uneasy when 10% of a population has a certain trait.
In applying these biases to the current study, almost all primary care physicians would not use ampicillin as first line therapy of acute cystitis because the national resistant rate is >30%. Many would feel very safe using ciprofloxacin since the resistance in most locations is very low, although it climbs to 17% in British Columbia.
The toughest issue is whether TMP-SMX can be used comfortably in most locations as primary therapy. Nationwide the rate of TMP-SMZ resistance was 16%, but it was higher and a little lower in some locations and in some populations. In an accompanying editorial, Lindsay Nicole, MD, an international scholar in the field of urinary tract infections, felt and I agree that TMP-SMZ can be used as first line therapy in acute cystitis. She cautions that even with the relatively low rates of resistance nationally in Canada, rates of resistance for the commonly used antimicrobials are rising for the most part. We should not generalize too much, as the response rate was only 4.5% of potential family physicians. More surveillance studies like these are needed with larger, perhaps more diverse, populations. For U.S. clinicians, the study is a window into simpler times in a more homogenous world. Gradually, however, the antimicrobial resistance world is changing even in Canada. We all must use our most innovative ideas to halt the snowball of antibiotic resistance and preserve the antimicrobial agents that remain.