The frequency of infections shows that children have a higher carrier rate than adults, up to 20%. The severity of infection results in about 1,200 to 1,900 deaths per year, with 11,000 to 24,000 cases per year. For epidemiology, the frequency of infections trends tend to show that the carrier rate in adults is lower than children, and children are up to 20%. The severity of infection, about 1,200 to 1,900 people die per year, and cases per year is about 11,000 to 24,000 cases per year.