National and Regional United States Antibiotic Resistance to Helicobacter pylori Resistance to Helicobacter pylori. Lessons from a Clinical Trial

Introduction

Although antimicrobial resistance to H. pylori has increased globally, resistance patterns have been shown to differ in relation to sex, age, ethnicity, life style habits, socioeconomic status, geographical distribution and particularly with national antibiotic consumption rates ¹. H. pylori is not yet included local, regional, and national susceptibility data. A 2015 study from the Houston VA Medical Center reported an increase of clarithromycin resistance among H. pylori from 9.1% in 2009-2010 to 24.2% in 2011-2013; 20.3% of the isolates were resistant to metronidazole. H. pylori resistance to tetracycline, amoxicillin, and rifabutin have remained historically low to absent in the US.

Here we report antimicrobial susceptibility from a randomized, double blind placebo-controlled U.S H. pylori eradication study conducted from 2017-2018 from clinical study sites across 20 states. The clinical results have previously been reported ². These data represent the largest survey of H. pylori antimicrobial susceptibility in more than 15 years.

Ethical Practices

The study protocol and all amendments were approved by the respective institutional review boards of participating institutions. All patients provided written informed consent before participating in the study.

Results

A total of 455 patients were enrolled in a double-blinded phase 3 clinical study which evaluated fixed dose triple therapy combination of amoxicillin-rifabutin-omeprazole vs. a fixed dose dual therapy comparator (amoxicillin -omeprazole). MICs were obtained for 345 clinical isolates recovered from treatment-naïve patients at 51 centers (20 states) across the US, representing 76% of the total number of patients enrolled in the study. The most common reason for failure of culture was improper storage or shipment of specimens. Additionally, a few isolates grew poorly on the Mueller-Hinton agar used for MIC determination, such that a reliable result could not be obtained.

Patients Demographics.

One hundred and thirty-one of 345 (38%) were male and the mean age of all patients was 46.4 ± 13 years (range 18-70 years). The majority of patients (263, 76.2%) were white, 71 (20.6%) were Black, and 11 (3.2%) were of other backgrounds (Asians were excluded from participation); overall, 208 (60.3%) identified as Hispanic. Enrollment was unevenly distributed across the different states.

Antimicrobial Susceptibility.

Across all sites, using the breakpoints listed above, the resistance rates were 0.0% for rifabutin, 6.4% for amoxicillin (95% CI: 3.8%-9.0%), 17.4% for clarithromycin (95% CI: 13.6%-21.4%), and 43.6% for metronidazole (95%CI: 38.3%-48.9%). and (Supplemental figures 1-4). Dual resistance to metronidazole and clarithromycin was 10.5%. The MIC₉₀ was 0.008 μg/mL for rifabutin, 0.125 μg/mL for amoxicillin, 8 μg/mL for clarithromycin, and 64 μg/mL for metronidazole. The majority of the isolates (93.6%) tested were susceptible to the drug combination used in the trial (amoxicillin plus rifabutin), using EUCAST breakpoints. Metronidazole resistance was associated with a Hispanic background (48.3% vs. 36.5% for non-Hispanics, P=0.035), with women (52.1% vs. 29.8% for males, P<0.0001) but not with age. Patients with clarithromycin resistance were slightly older (50.1 ± 11 years vs. 45.6 ± 13 years, P<0.01). Among the 71 isolates tested for levofloxacin and tetracycline resistance, 41 (57.8%) were resistant to levofloxacin and 2 (2.8%) were resistant to tetracycline (Supplemental figures 5-6). As observed with clarithromycin resistance, patients with levofloxacin resistance were older (53.3 ± 9 years vs. 45.3 ± 11 years, p=0.002). Importantly, almost one quarter (17/71 or 23.9%) of patients with clarithromycin resistance had dual resistant to levofloxacin. Twenty-two of 71 (31%) with clarithromycin resistance had dual resistance to metronidazole and levofloxacin; 16.9% (12/71) of the isolates were resistant to all three antibiotics.

In order to better describe the data from a geographic perspective, the US was divided into 3 regions East, Central and West to allow visualization and comparison across regions (Table 1). Clarithromycin resistance ranged from 11.1% in the Western US to 23.2% in the Eastern states (p=0.03). Metronidazole resistance was high in all regions ranging from 35.5%-49.7%. Amoxicillin resistance ranged from 5.3% to 8.3%. Because of the smaller numbers tested for resistance to levofloxacin or tetracycline it was not possible to detect whether there were significant regional differences.

Table 1.

Geographical distribution of antimicrobial resistance patterns per U.S. region, 2017-2018

Antibiotic	All isolates n=345	West n=108	Central n=86	East n=151	P-value
Amoxicillin	6.4% (22)	8.3% (9)	5.8% (5)	5.3% (8)	0.6
Clarithromycin	17.4% (60)	11.1% (12)	15.1% (13)	23.2% (35)	0.03
Metronidazole	43.6% (150)*	35.5% (38)*	43.0% (37)	49.7% (75)	0.08
Rifabutin	0.0% (0)	0.0% (0)	0.0% (0)	0.0% (0)	ND
	Limited Analysis n=71	n=19	n=19	n=33
Tetracycline	2.8% (2)	5.3% (1)	5.3% (1)	0 (0.0%)	0.3
Levofloxacin	57.8% (41)	57.8% (11)	68.4% (13)	17 (51.5%)	0.5

^*Metronidazole susceptibilities were available for 107 isolates from the West region and 344 isolates in total.

Discussion

Overall, we found that the proportion of US isolates with resistance to clarithromycin (17.6%) metronidazole (43.6%), and levofloxacin (57.8%) were higher compared to previous reports. As noted above, this study showed high rates of metronidazole resistance across all regions. No isolate was resistant to rifabutin. Amoxicillin and tetracycline resistance were both observed albeit at low rates (amoxicillin resistance 6.4% and tetracycline resistance 2.8%).

In both treatment arms of the prior study amoxicillin resistance had a small but measurable effect on treatment outcome ². In contrast, resistance to clarithromycin, metronidazole, or levofloxacin is highly correlated with treatment failure when they are used in triple therapies. There was also a poor correlation between outcome (cure or failure) with individual isolates and the measured MIC resistance breakpoint for amoxicillin with the dual high dose PPI and amoxicillin treatment arm. Interpretation of the effect of amoxicillin resistance on outcome in the dual therapy are were further complicated by the fact that the cure rate with the dual therapy was low (i.e., 57.7%) which was however consistent with prior US studies of similar therapy ^3-5. Clarithromycin resistance differed significantly across the regions (P=0.03) with the greatest resistance observed in the East. Metronidazole resistance was high in all regions.

These results are consistent with the global increase in antimicrobial resistance and underscores the most recent H. pylori guidelines to no longer prescribe clarithromycin, metronidazole, or levofloxacin–containing triple therapies ^{6, 7}. The general unavailability of readily accessible H. pylori culture and susceptibility testing requires treating physicians pay close attention to the results of testing for cure to alert them when therapies become ineffective ⁸. The recently introduced rifabutin triple therapy (Talicia®) and bismuth quadruple therapy are the only currently available regimens in the U.S. for which H. pylori resistance is rare. The commercially available bismuth formulation, Pylera® is often inconvenient to prescribe as it is packaged for 10 day therapy whereas treatment guidelines recommend 14 day therapy for optimal effectiveness⁸. Local antimicrobial resistance rates are needed to allow for clinicians to reliably and successfully eradicate H. pylori infections.