Test and treat strategies for Helicobacter: PATIENTS AND METHODS part 2
In each arm, the first-line regimen for H pylori eradication was omeprazole 20 mg, clarithromycin 500 mg and metronidazole 500 mg bid for seven days (OCM). The second-line regimen, used for OCM failures, was omeprazole 20 mg bid, clarithromycin 500 mg bid and amoxicillin 1000 mg bid for seven days. When a third attempt at H pylori eradication was necessary, ranitidine 150 mg bid, bismuth subsalicylate 524 mg qid, metronidazole 250 mg qid and tetracycline 500 mg qid were prescribed for two weeks. Probability inputs: Point estimates of path probabilities for the decision tree were extracted from a review of the published literature (Table 1). Articles were identified from computerized searches of the MEDLINE database (1966 to 1998) and from hand searches of recent review article bibliographies. For each probability, a plausible range of values for sensitivity analysis was chosen to reflect uncertainty in the literature. Where a necessary probability could not be found in the literature, a reasonable point estimate was chosen empirically and a wide range of plausible values was used for the sensitivity analysis.
The prevalence of H pylori infection among dyspeptic patients was assumed to be 30% (range 10% to 50%). Among H pylori-positive patients, the prevalence of PUD was assumed to be 35% (20% to 50%) versus 3% among those without Hpylori. The sensitivity and specificity of the C-UBT for detection of H pylori were estimated at 96% and 98%, respectively (70% to 100%). The Hpy- lori serology assay was assigned a sensitivity of 85% and a specificity of 79% (70% to 95%) based on a published meta- analysis and a third-party technical review.
The effectiveness of H pylori eradication therapy was assumed to be 90% (range 60% to 100%). With successful eradication, 95% of ulcers were assumed to heal versus 76% if eradication failed. A four-week course of rani- tidine was considered to heal 70% of ulcers, while a six-week course of omeprazole monotherapy healed 90%. H pylori-negative patients who were given eradication therapy in error because of a false-positive noninvasive test were assigned an ulcer healing rate of 85% because they had received a seven-day course of omeprazole.
The one-year recurrence rate of H pylori-positive PUD without maintenance therapy was assumed to be 70% (50% to 100%), while that following successful eradication of the organism was assumed to be 4% (0% to 20%). Throughout the model, it was assumed that 75% of ulcers were symptomatic and 1% of new ulcers presented with complications such as bleeding or perforation.
TABLE 1 Probabilities applied in the decision analysis model
Variable |
Base case probabilities |
Probability ranges for sensitivity analysis |
Reference(s) |
Prevalence of |
0.30 |
0.10-0.50 |
17-21 |
Prevalence of PUD if H pylori-positive |
0.35 |
0.20-0.50 |
22 |
Prevalence of PUD if H pylori-negative |
0.03 |
N/A |
22 |
Sensitivity of 13C-UBT |
0.96 |
0.70-1.00 |
23-25 |
Specificity of 13C-UBT |
0.98 |
0.70-1.00 |
23-25 |
Sensitivity of serology |
0.85 |
0.70-0.95 |
26,27 |
Specificity of serology |
0.79 |
0.70-0.95 |
26,27 |
Effectiveness of H pylori eradication |
0.90 |
0.60-1.00 |
28,29 |
PUD healing after four weeks of ranitidine |
0.70 |
N/A |
30,31 |
PUD healing after six weeks of omeprazole |
0.90 |
N/A |
30,31 |
PUD healing after one week of omeprazole |
0.85 |
N/A |
30,31 |
Recurrence rate of PUD over one year if H |
0.75 |
0.05-1.00 |
32,33 |
Recurrence rate of PUD over one year if H |
0.04 |
0-0.20 |
32,33 |
Proportion of ulcers with associated symptoms |
0.75 |
N/A |
32 |
Relapse rate of NUD |
0.65 |
0.00-1.00 |
37 |
Because no therapy has demonstrated conclusive efficacy in NUD, the symptomatic response rate of NUD to any therapy was considered equivalent to the placebo response rate reported in clinical trials. In particular, despite recent controversy, no benefit was assumed from H pylori eradication in H pylori-positive NUD (34-36). Hence, the one-year symptomatic relapse rate regardless of therapy was estimated to be 65% (0% to 100%).
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