Introduction to epidemiology
QQESILQN I;
In 2013, a group of3602 men and women aged 15-3oyearswere recruited from the North
West province of South Africa and assessed for human immunodeficiency virus (HIV). 160
participants were found to have HIV when tested at baseline. Participants who did not test
positive for HIV in 2013 were followed-up and tasted again alter 3 years of follow-up (only
those who previously had tested negative for HIV were tested again at follow-up). A further
76 cases of HIV were identified during this 3 year period (either diagnosed during the interim
or diagnosed during the study assessment).
Data from this study are presented in the following table (Table I), stratified by sea.
Table I
No. of Prevalent Prevalent Person Loss to Deaths Incident
participants cases at cases years follow- in those HIV
recruited baseline remaining of up in HIV cases at
at follow- follow- those negative follow!-
up†up HIV at up
negative baseline
at
baseline
Males 1,693 45 37 2.530 143 4 30
Females 1,909 l 15 107 2,632 l 17 6 46
Total 3.602 160 144 5.162 260 10 76
It is assumed that once participants contract HIV they remain HIV positive, and that over
the follow-up period some of these cases detected at baseline were lost to follow-up.
(a) What is the study design used in this study? [I mark]
(b) What was the prevalence of HIV in (i) males and (ii) females aged 15-30 in 201 3? [3
marks]
(c) What was the prevalence of 111V in (i) males and (ii) ferrules alter 3 years of follow-up?
[3 marks]
(d) What was the cumulative incidence of HIV among (i) make and (ii) females over the 3
year study period? [4 marks]
hat was the incidence rate of HIV among (i) males and (ii) females for the 3 years? [4
arksl
(1) Is cumulative incidence or incidence rate a better reflection of the incidence of HIV in
this study population? Please justify your answer. [2 marks]