does tuberculosis have a seasonal pattern among migrant population entering iran?

background there are few quantitative documents about the seasonal incidence of tuberculosis (tb) among immigrant populations. concerning the significant role of recognizing seasonal changes of tb in improving the tb control program, this study determines the trend and seasonal temporal changes of tb among immigrants entering iran.   methods in this longitudinal study, data from the iranian tb register program (from 2005 to 2011) was used. the aggregated number of monthly and seasonal tb cases was obtained by adding the daily counts. data was analyzed by chi-square, independent t-test, anova, and poisson regression using stata 11 and spss 20 software.   results among 74,155 registered patients with tb, 14.3% (10,587) were non-iranian who had immigrated to iran from 29 different countries. the highest aggregated number of seasonal and monthly incidence of tb in immigrants was observed in spring (2824, p= 0.007) and in may (1037, p< 0.001). the number of non-iranian patients with tb increased significantly over the years (β= 0.016, p= 0.001).   conclusion this study shows that immigrants constitute a significant portion of tb patients recorded in iran and this trend is increasing. also, the peak incidence of this disease is the second month of the spring.