Active Case Finding Among Homeless People as a Means of Reducing the Incidence of Pulmonary Tuberculosis in General Population

The incidence of tuberculosis (TB) declined more than two-fold, compared with the national average, in the northeastern region of Poland in the period of 2003-2012. During that time, four programs of active case finding of TB were conducted as part of which a total of 944 homeless individuals were examined and 21 cases of active TB were detected. The objective of the present study was to find out whether the observed beneficial epidemiological trend could be a result of those programs. We addressed the issue of how the active case finding programs in the homeless community affected the TB incidence in the general population using a modified crisscross SIS-type (Susceptible-Infected-Susceptible) model which describes the dynamics of TB spread between the homeless and non-homeless populations. The values calculated from our model proved highly congruent with the actual epidemiological data. Our analysis showed a significant decline in TB incidence within 1 year of completion of each active case finding program. The model shows that each identified and cured case in the homeless community reduced the number of new cases in the general population by 3-4 within 1 year and by up to 20 within 5 years.