Shigella infection has affected three persons who consumed hotel food in Nilambur and several school students in Vadakara, prompting health department to intensify preventive measures. Kozhikode: Following confirmation about outbreak of Shigella infection in Keralam s Kozhikode and Malappuram districts, health authorities have stepped up preventive measures through rigorous inspections, sanitation drives and awareness campaigns to prevent further spread of the infection.