Probiotics and respiratory tract diseases.

In a double-blind randomized controlled trial (DBRCT) in 1,000 shift workers [23] the intake of fermented milk drinks containing Lactobacillus casei DN114 001 twice daily reduced the occurrence of CID during the cold season, the time until infections occurred and the duration of fever episodes. During infections the counts of leucocytes, granulocytes and natural killer cells were enhanced. In a multicentric, likewise DBRCT in 1,072 elderly the intake of the same drink reduced the mean duration of CID [24] . During the consumption period of 3 months the average duration of a CID episode has been significantly shortened to 6.5 versus 8 days in the control group (p = 0.008) as well as the cumulative duration of CID (7 vs. 8 days in the control group; p = 0.009). The reduction in both episode and cumulative duration was also significant for all upper respiratory tract infections and for rhinopharyngitis. In conclusion, the consumption of a fermented dairy product containing the probiotic strain L. casei DN-114 001 in elderly was associated with a decreased duration of CID and results in enhanced resistance of the elderly to CID. Like elderly and shift workers, children show higher susceptibility to infections. Intense contacts in day care centers and schools predispose to transmissions of respiratory infections, which often result in missed days of both day care and parental work. Several studies have shown effects of probiotics on diarrhea [11–16] . In Common infectious diseases (CID) of the airways and the gastrointestinal tract are still a considerable cause of morbidity and mortality in the elderly as aged people experience more frequent and severe community-acquired CID. Oral administration of specific probiotics has been reported to influence defense by the host in a beneficial way by modulating the immune system and increasing the transepithelial resistance [1–9] . Several studies documented that certain probiotics increase the number and activity of natural killer cells [3, 10] , enhance antibody response to vaccination [1, 2, 4, 7] and increase the rate of seroprotection and seroconversion [1] . Probiotics were not only shown to enhance immune responses at the systemic level [8, 9] , but there is also evidence for beneficial effects on the prevention and management of infections by probiotics [10] . For instance, it has been shown that probiotics reduce the risk of diarrhea including traveller’s diarrhea [11–13] . Furthermore effects on the severity, duration and incidence of CID were demonstrated in a number of clinical trials [4, 14–25] . A meta-analysis of 8 controlled trials [26] showed a decrease in the occurrence of respiratory tract diseases as defined by the number of persons having at least 1 episode during the observation period. In this meta-analysis the severity and duration of the episodes was not significantly affected. Published online: September 8, 2010