AIM:The widespread use of antibacterial therapy hasbeen suggested to be the cause for the decline in theprevalence of Helicobacterpyloriinfection.This studyexamine the serial changes of urea breath test resultsin a group of hospitalized patients who were givenantibacterial therapy for non-gastric infections.METHODS:Thirty-five hospitalized patients who weregiven antibacterial therapy for clinical infections,predominantly chest and urinary infections,werestudied.Most(91%)patients were given singleantibiotic of either a penicillin or cephalosporin group.Serial 13C-urea breath tests were performed within 24hours of initiation of antibiotics,at one-week and atsix-week post-therapy.H.pylori infection wasdiagnosed when one or more urea breath tests waspositive.RESULTS:All 35 patients completed three serial ureabreath tests and 26(74 %)were H.pylori-positive.Ten(38 %)H.pylori-infected patients had at least onenegative breath test results during the study period.The medium delta ~(13)C values were significantly lowerat baseline(8.8)than at one-week(20.3)and six-week(24.5)post-treatment in H.pylori-positive individuals(P=0.022).Clearance of H.pyloriat six-week was onlyseen in one patient who had received anti-helicobactertherapy from another source.CONCLUSION:Our results suggested that one-third ofH.pylori-infected individuals had transient false-negative urea breath test results during treatment withantibacterial agent.However,clearance of H.pyloriInfection by regular antibiotic consumption is rare. AIM: The widespread use of antibacterial therapy hasbeen suggested to be the cause for the decline in theprevalence of Helicobacterpylori infection. This studyexamine the serial changes of urea breath test resultsin a group of hospitalized patients who was givenantibacterial therapy for non-gastric infections. METHODS: Thirty -five hospitalized patients who weregiven antibacterial therapy for clinical infections, predominantly chest and urinary infections, were sturdied. Host (91%) patients were given single antibiotic of either a penicillin or cephalosporin group. Ser 13 C-urea breath tests were performed within 24hours of initiation of antibiotics, at one-week and atsix-week post-therapy. H.pylori infection wasdiagnosed when one or more urea breath tests was positive. All 35 patients completed three serial urebreath tests and 26 (74%) were H. pylori-positive .Ten (38%) H. pylori-infected patients had at least one negative breath test results during the study period. The medium delta ~ (13) C values were significantly lower than baseline (8.8) at at least one week (20.3) and six-week (24.5) post-treatment in H. pylori-positive individuals (P = 0.022). Clearance of H. pyloriat six-week was only one in one patient who had received anti-helicobactertherapy from another source. CONCLUSION: Our results suggested that one-third of H.pylori-infected individuals had transient false-negative urea breath test results during treatment withantibacterial agent. Host, clearance of H.pyloriInfection by regular antibiotic consumption is rare.