Question

At four UK hospitals, patients with severe asthma were screened for fungal sensitization by skin prick testing. those 3,610 who were positive by skin prick were randomized to one of two treatment regimens: 1,805 were assigned to take an antifungal agent in tablet form while 1,805 were assigned to take a similar looking placebo tablet. The primary end point was the development of a particular type of lung infection by 32 weeks. By the end of the study, 1,492 of those who had taken the antifungal agent had not developed the lung infection, whereas 1,064 of those who had taken the placebo had not developed the lung infection. There was no loss to follow-up and no censoring except for administrative censoring.

a) What is the study design?

b) Generate a contingency table:

	Lung Infection (+)	Lung Infection (-)	Total
Antifungal group	313
Placebo group	741
Total	1054

c) Calculate the 32-week cumulative incidence for those exposed and unexposed to the antifungal agent, respectively. (CI= #new cases of disease during a given time period/total population at risk)

d) Calculate and interpret the risk ratio between exposed group and unexposed group. (RR= CI exposed/ CI unexposed)

Answer 1

a) The objective of the study is to screen for fungal sensitization in patients with severe asthma by skin prick testing for 32 weeks. The number of patients who showed positive results for skin prick were 3610. They were randomly subjected to one of two treatment regimens. The two treatment regimens are: a) one of the group took antifungal agent in tablet form b) another group took a similar looking placebo tablet. Presence of lung infection was assessed in both the groups.

b)

	Lung Infection (+)	Lung Infection (-)	Total
Antifungal group	313	1492	1805
Placebo group	741	1064	1805
Total	1054	2556

c)Cumulative Incidence= new cases of disease during a given time period/total population at risk

=1054/3610

=0.292

d) CI exposed= Sum of number of patients with lung infection in both the groups

CI unexposed= Sum of number of patients without lung infection in both the groups

Risk Ratio= CI exposed/ CI unexposed)

=1054/2556

=0.412