Question

the population of a town is 3000. in September 2013, the enrolment in primary school of this town was 455. at the beginning of school year all student were free of head lice. On October 3,2013 six cases of head lice were brought to the attention of the school principal. 32 cases of lice were discovered in the school by the end of month ad one case had comleted succesful treatment. On Nov. 2013, 45 new cases were identified in the community of this town. By the end of Nov. all cases remain under treatment. a) what was the incident rate per 100 of head lice at the school in the month of October 2013? b) Assuming there were no changes in the size of the population on the town, what was the period prevalence of head lice in the community over the moth of Nov. 2013.

Answer 1

a. Incidence rate =

Number of new cases of disease or injury during specified period / Time each person was observed, totalled for all persons

Divide the population size by 100 i.e 3000/100= 30

Total number of cases 3+32+45=80

Incidence rate in the community per 100 = 80/30 = 2.66

Incidence rate in the school

Population /100 = 455/100 = 4.55

Number of cases in school = 35

Incidence rate = 35/4.55= 7.69

b. Period prevalence (ratio) = Number of cases that existed in a given period ÷ Number of people in the population during this period

Number of cases that existed in a given period (November 2013)= 45

Number of people in the population during this period = 3000

Period prevalence over the month of November 2013 = 45/3000 =0.15