Yes, this is O157:H7, not ExPEC. Bully for you.
One thing regarding popular accounts of antibiotic resistance I’ve noticed is that there is an overemphasis on the evolution of resistance, and an underemphasis on the spread of resistant bacteria. While the evolution of resistance is important, most of what we see in a hospital is not the de novo change of a sensitive strain into a resistant one (i.e., evolution), but, instead, the survival and spread of already resistant bacteria in this antibiotic-laden environment.
What this means is that changes in the frequency of resistant organisms, for better or for worse, depend not only on antibiotic use, but also on other ecological dynamics–that is, because of clonal spread. In other words, a resistant strain might not become more common because it is resistant, but because it does something else better than most other strains (e.g., it might be hard for the immune system to recognize and attack it).
A recent paper about antibiotic resistance in E. coli that cause urinary tract infections (‘UTI’) indicates that clonal spread is driving antibiotic resistance. The researchers collected a total of 780 isolates of E. coli from every referred patient at a university health center with UTI during a 14-week period for four consecutive years.
What they found was that there was no trend (up or down) in the frequency of resistance to trimethoprim-sulfamethoxazole, ciprofloxacin, cephalothin, or nitrofurantoin. Only ampicillin (amoxicillin) decreased significantly from year three to year four. Shortly before the study began, the health center switched treatment of UTI from trimethoprim-sulfamethoxazole to either nitrofurantoin or ciprofloxacin, yet the prevalence of resistance to all three of these drugs remained unchanged.
The authors also looked at the genetics of these strains. Most of the UTI were caused by a limited number of genotypes (genetic lineages), some of which are drug resistant. The odds of women without common exposures would be infected with this limited subset of genotypes is quite small. In fact, if drug use were generating novel resistant strains, we would expect to see many more resistant genotypes. Instead, what we see is the ‘sorting’ of pre-existing resistant UTI E. coli, and this sorting appears to be independent of antibiotic use.
So what does this mean for public health policy?
Trying to treat a particular problem, such as a drug resistant UTI-causing E. coli will not work in isolation. Like within-household transfer, where it might be necessary to treat asymptomatic family members and pets (who carry these resistant organisms), we have to ’embiggen’ (to use Madame Wev‘s phrase) the scale on which we envision the problem–this is not a problem that starts at the hospital door. We also need to determine what the reservoirs of these resistant UTI strains are (i.e., where else they live), and attempt to limit the spread from those reservoirs.
Cited article: Smith SP, Manges AR, Riley LW. Temporal changes in the prevalence of community-acquired antimicrobial-resistant urinary tract infection affected by Escherichia coli clonal group composition. Clin Infect Dis. 2008 Mar 1;46(5):689-95.