Risk for latent tuberculosis infection among household and non-household contacts of TB cases in an urban African setting

Statement of the Problem: Tuberculosis remains a major global public health problem. About 25 percent of the worlds population is infected with Mycobacterium tuberculosis (M. tuberculosis). Although individuals with latent tuberculosis are not infectious, they are at risk of developing active disease and becoming the next pool of infectious individuals. Studies show that risk for progression to disease once infected may range from 5% in children who are recently exposed to as high as 16% among individuals infected with the human immunodeficiency virus. Purpose: To identify individuals in the community who are latently infected with tuberculosis. Methods: We conducted two inter-related studies; Study 1 was to examine the effect of household and non-household exposure to an infectious tuberculosis case on the prevalence of latent tuberculosis infection in the community. We identified index TB cases and matched them with controls who in turn enumerated their social contacts who were then approached and asked to participate in the study. Diagnosis of latent tuberculosis infection was by tuberculin skin test. The second was an incident cohort study to investigate whether differences in the prevalence of latent tuberculosis infection between men and women observed in previous studies could be due to differences in the incidence of latent tuberculosis infection. A cohort of tuberculin skin test negative individuals was enrolled between 2014 and 2016 and were followed -up and a repeat TST was placed to determine tuberculin skin test conversion. Main results: Infection was highest among household case contacts and lowest in household contacts of controls. Prevalent infection among non-household case contacts was similar to that of non-household control contacts. The incidence study found that men had a higher risk for infection than women. Fifty-one percent of converters were men representing an incidence rate of 16.2 per 100PYO while 48.4% of the converters were women representing an incidence rate of 10.6 per 100PYO among women.