- Background: Acute diarrhea is a common disease worldwide and in Israel, a Mediterranean country. Acute bacterial gastroenteritis (ABGE) is the leading cause of severe diarrhea in Israel in summer and early autumn. Although there are some reports showing some benefit from empiric antibiotic therapy in acute gastroenteritis, most are old reports using nondefinitive diagnostic criteria and using 5-day antibiotic regimens. Aims: 1. To examine the efficiency of antibiotic therapy in relatively severe ABGE in general. 2. To check the efficiency of the different types of quinolones in the treatment of ABGE. 3. To compare various therapy regimens. Methods: All patients admitted to the Barzilai Medical Center emergency room during the period June to October in 2002-2004 who were defined by protocol as having relatively severe gastroenteritis and required hospitalization in the Department of Internal Medicine were included in the study. All were randomized either to a supportive treatment only group (STG) or to the antibiotic treatment group (ATG) of ofloxacin or levofloxacin with a single dose or BID for 5 days in addition to STGs. All patients were interviewed a week later about their medical history and duration of symptomatology. Results: One hundred thirty-nine patients were found eligible for the study in the above-mentioned period. Abdominal pain resolved 1.3 days earlier in the ATG in comparison to the STG whereas vomiting and diarrhea disappeared 1.0 and 0.8 days earlier, respectively, in the ATG versus the STG. In terms of fever abatement there was no difference between the regimens and no significant difference in symptomatology disappearance between various types of quinolones used or between the single antibiotic dose regimen and the 5-day antibiotic regimen groups. Conclusions: 1. Antibiotic therapy was found to shorten duration of symptoms in patients with relatively severe gastroenteritis. 2. Single-dose therapy is as effective and certainly significantly more cost effective in comparison to the 5-day antibiotic treatment regimen.