Background: An outbreak of fever and cough was notified to public health authorities by the management of school X among their students, Kozhikode district, Kerala, on Jan 1, 2020. We conducted an outbreak investigation to confirm the diagnosis, describe the case patients by time, place, and person, and propose appropriate recommendations. Materials and Methods: We defined a probable case of influenza as any student or staff of school X, Kozhikode district with a fever and cough between Dec 30, 2019, and Jan 14, 2020. We conducted an active case search and contact tracing in the school. We described the cases by date of symptom onset using an Epicurve, plotted cases by their classroom, and calculated the attack rate by age, and gender. Results: We identified 270 cases of influenza; among them, 264 (98%) were students, and 6 (2%) were the staff. The overall attack rate was 36%. The attack rate was higher among the students (39%) than the staff (12%, 6/49, P < 0.0003). The attack rate was higher among students of class 10E (90%, 37/41) and class 10A (80%, 33/41), where the index case had contact with the students during the symptomatic phase. Conclusion: An outbreak of influenza A (H1N1) occurred among students and staff, predominantly affecting the 10th division. School and health authorities implemented several interventions to limit the outbreak, including training students on personal hygiene. We recommended conducting surveillance of influenza, maintaining adequate spacing of benches, self-hygiene practices, and classroom ventilation.
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