Reactivity of tuberculin among Bacillus Calmette-Guérin vaccinated school children, Kassala State, Sudan Fatima A. Khalid1. Elderidiry MM2, MM Mukhta3

Abstract Background Tuberculin skin test (TST) is a delayed hypersensitivity reaction of latent TB infected patients and BCG vaccinated individuals. It is recommended for screening of mycobacterium infection in many countries. Kassala state in eastern Sudan is known as the highest pulmonary TB endemic region in Sudan. Little data is available on the TST reactivity among school children in Kassala. This activity aimed to measure the prevalence of TST reactivity among school children in Kassala as indictor for exposure and response to BCG vaccination. Method Five tuberculin units of PPD were injected intradermally in the left forearm of 2600 children aged 5-15 years attending governmental basic schools in Kassala. BCG scar, child health and nutrition status were assessed before the test. The reactivity of TST was read for 2568 children after 48- 72 hours, interpreted at different cut-off level based on published guidelines. Data were analyzed using SPSS (V. 20.0) Results Tuberculin reactivity was measured to 2568 out of the 2600, 32 were absent during the measurement. Most of children 2100 (81.8%) had no reaction with TST (no induration). Four hundred and sixty eight (18.2%) had induration ranged from 1mm to 28 mm with mean 3.1mm ±3.29, among them, 17 cases had induration ranged from 10- 28mm. prevalence of BCG scar was 1688 (64.9%). TST reactivity was statistically associated with geographical localities, child gender, and age (P<0.001). High percentage of TST reactivity was recorded in females (65.8%) compared to males (34.1%). Furthermore, TST reactivity was increased with the age, among the strong positive reaction, 9/17 were in age 13-15 years. Also TST reactivity was statistically correlated with nutrition and socioeconomic status ((P<0.001). TST reactivity was not affected by BCG vaccine (P>0.05). Conclusion The study provides data on BCG vaccination coverage in Kassala state, the prevalence of non reactivity of TST. No effect of BCG vaccine on reactivity of TST, hence it can be used as the diagnostic tool for detection of LTBI in children. Different confounding factors were associated with TST reactivity including child age, gender and nutrition status, health and socioeconomic status.