Second, travelers’ diarrhea had a distinct seasonal pattern with spring and summer surges, but this seasonality may largely depend on age. Third, travel to some parts of Asia and Africa was significantly associated with contracting diarrhea. We illustrated chronological trends of diarrhea (Figure 1), and found that the disease incidence exhibited a similar yearly pattern for 2001 to 2005, even during periods of marked negative impacts on international tourism. Travel activities and hygiene behaviors might not be affected by terrorism or disease outbreak. This phenomenon has not been reported so far, and could only be confirmed by find more longitudinal observations, which are scarce for reports

of travel-related illnesses.8 Since diarrhea incidence is likely to continue

showing this pattern, these findings must be used to develop plans directed at public health initiatives to prevent travelers’ diarrhea. Summer is generally considered to be the riskiest season for contracting diarrhea in the northern hemisphere,1,21 because it is often difficult to maintain food hygiene in warmer weather.10 The increased incidence of diarrhea observed in August and September in our study supports this assumption. However, the high incidence in March requires another explanation. In Japan, the fiscal year ends in March, and most colleges and universities have spring break during this month. Considering the age distribution among travelers with diarrhea, the high incidence in March may be due to increased travel among college/university Alpelisib students, although we do not have data to support this out hypothesis. Traveler age and sex distribution are associated with the travel patterns adopted by each age category. For example, young women travelers outnumber males in the same age group because of their travel preferences,19,20 whereas middle-aged men travel more than women in the same age category for their business activities.19,20 Those aged 20 to 29 years showed a higher incidence of travelers’ diarrhea than other age groups, a finding consistent with

other reports.3,5,6,9,21 This may reflect the relatively more adventurous and careless behavior6,22 or larger appetite in this age group.1 Differences in disease incidence between sexes might be ascribed to hygiene behavior, destination, and purpose of travel. For instance, young men are more adventurous and thus show higher incidence of travelers’ diarrhea than young women in general. However, many studies have not shown any significant differences in travelers’ diarrhea by gender.6,13,22 In contrast, our results indicate that the difference in incidence between sexes largely varies by age. Additional studies will be needed to determine the reasons behind our findings. Our study revealed that travel to south-central Asia, Southeast Asia, and North Africa is positively associated with contracting diarrhea.