The Effect of Age Group under 15 Years on Cholera Morbidity during the Past 10 Years in Iran (1996-2005)

Objective: The study of the effect of age, especially children under 15 years, on cholera morbidity during a period of ten years (1996-2005) was carried out in Iran. There are no other studies on this topic in Iran and other countries.
Methods: In this cross sectional study, we used cholera surveillance data collected in Center for Disease Control. All cholera cases were divided into two groups: under 15 years and above 15 years. Incidence rate of cholera per 100000 was calculated in total population and the two mentioned groups during 10 years. The relative risk of less than 15 year-olds group to above 15 year-olds was calculated with95 % CI for 10 years by EPI6 and SPSS software.
Findings: The trend of cholera incidence during the past 10 years shows two epidemic peaks in 1998 and 2005 by the rate of 15.7 and 1.63 per 100000, respectively. During the year with no epidemic and the years between two peaks, the age group under 15 year-olds was more affected with significant relative risk. For example, in 2001 this rate was 4.53. So, we can consider this age group as a risk factor to cholera morbidity. The age group of above 15 year-olds was more affected to cholera during epidemic years (1998, 2005) and relative risk was less than one. So, the age was protective on cholera morbidity for children in these years.
Conclusion: One of the most important causes of periodic cholera epidemics every 5-6 years is changing of herd immunity. During the years between two epidemics adults have sufficient immunity and children are more affected because of first exposure and less immunity. With reduced herd immunity epidemics occur. We recommend continuing and strengthening of cholera surveillance system for detection of epidemics and treatment of highly sensitive age groups.