Question

Infant feeding practices and the risk of infant HIV infection at 3months of age in Johannesburg were assessed in a cohort study. A total of 941 HIV infected mothers and their infants (HIV negative) were enrolled . These mother infant pairs were divided into exposure groups with respect to feeding practices, including exclusive breastfeeding (n=91) and mixed feeding (n=355). By three months of age , eleven (11) of the exclusively breastfed babies and seventy seven (77) of the mixes feeding babies had developed HIV infection.

Construct a two dimensional contingency table (2*2) of the above data?

Calculate and compare the incidence of outcome (HIV status ) in the two groups

Please offer an explanation or interpretation of your result

Answer 1

A two dimensional contingency table is a table used to examine the relationship between two categorical variables . It displays the frequency distribution of the variables.

Contingency table

CONTINGENCY TABLE x2 Number of Brea Breaot an态techo deve- Tuesday (108-257) Week 16 HIV-1 No HIV Breast

Incidence of HIV in two groups :-

Incidence of HIV in breastfeeding infants = Number of breastfeeding infants developed HIV / Total number of breastfeeding infants

= Number of breastfeeding infants who developed HIV / Total number of breastfeeding infants

= 11/ 91

= 0.12

Incidence of HIV in mixed feeding infants = Number of mixed feeding infants who developed HIV / Total number of mixed feeding infants

= 77/ 355

= 0.21

Hence, the infants who were mixed feeded had higher incidence rates of developing HIV .