Background There is insufficient evidence of preventive effect of probiotics on upper respiratory tract infections (URTIs) in an elderly population. Methods We conducted a multicenter, double-blinded, randomized, placebo-controlled parallel group study. Elderly persons had participated who used day care at 4 facilities in Tokyo. We used fermented milks containing Lactobacillus casei strain Shirota (LcS) and placebo drinks as test drinks. Results A total of 154 subjects was analyzed. The number of persons diagnosed with an acute URTIs was almost identical in both groups (LcS: 31, placebo: 32), whereas the number of acute URTIs events (LcS: 68, placebo: 51) and the symptom score (LcS: 425, placebo: 396) were both higher in the LcS group. Permutation tests performed using the total number of acute URTIs infection events/total days of observation and the total symptom score/total days of observation found no statistically significant difference respectively (P values of.89 and.64, respectively). Comparing the mean duration of infection per infection event found a shorter mean duration in the LcS group (LcS: 3.71 days, placebo: 5.40 days), and the difference was statistically significant. Conclusion The results suggest that fermented milk containing LcS probably reduces the duration of acute URTIs.
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