Prevalence and demographic determinants of metronidazole resistance by Helicobacter pylori in a large cosmopolitan cohort of Australian dyspeptic patients

Background: The pre-treatment sensitivity of Helicobacter pylori to metronidazole is a key determinant of successful eradication therapy and should influence local choice of therapy. However, there are few data defining the prevalence of metronidazole resistance (MR) in Australia. Aim: To determine prospectively the prevalence and demographic determinants of MR in H. pylori isolates from a large and cosmopolitan cohort of dyspeptic patients in Sydney. Methods: Consecutive dyspeptic patients undergoing endoscopy had gastric biopsies for histology, urease test and culture. Metronidazole resistance was determined by E-test after subculture. An MIC >8 μg/mL defined MR. Patient age, gender, birthplace and history of previous nitroimidazole use were recorded. Results: In 732 patients, H. pylori was present in 46.4%. Culture was successful in 81% and subculture for MR in 88% of these. In 237 evaluable patients the overall MR rate was 59.1%. Five patients had had prior triple therapy for H. pylori (of which four of five had MR). Therefore, the primary MR rate in the study population was 58.6% (136/232). MR was more prevalent in younger patients (p=0.0002). The MR rate was 70.4% in patients 18-39 years, 66.7% in those aged 40-59 years and lowest (38.9%) in those 60 years or older (p=0.002). The MR rate was highest in patients born in Southeast Asia (72.8%, 59/81) and significantly higher than in Australian born (48.1%, 26/54), or Southern European (46.2%, 24/52) born patients (p=0.002). There was no gender difference. Logistic regression to determine the impact of each variable (birthplace, age and gender) on MR identified Southeast Asia birthplace as a factor associated with greater likelihood of harbouring an MR isolate (OR 1.88, p=0.02). Southern European born patients had the lowest risk of MR (OR 0.70, p=0.02) as did patients older than 60 years (OR 0.56, p=0.04). A definite history of prior metronidazole use was infrequent and not predictive of MR. Conclusions: While a high rate of MR is not unexpected in patients born in developing countries, the high rate in Australian born patients is surprising and of concern. This may relate to the high local usage of nitroimidazoles as monotherapy and has important implications for the effectiveness of metronidazole containing triple therapies.