Lessons from an outbreak investigation and retrospective cohort study of influenza in a medical college in Uttar Pradesh, India, 2022

Integrated Disease Surveillance Programme, Uttar Pradesh (UP), India, notified a suspected Influenza cluster in medical college A in September 2022. We conducted an outbreak investigation and retrospective cohort study to describe the epidemiology and assess risk factors. We defined a probable case as a student/ staff of College A having sudden onset fever with headache/ body ache/ cough between 8 September-17 October 2022. A confirmed case was Influenza RT-PCR positive student/ staff of College A during the same period. The cohort was all the students and staff of College A. We documented sociodemographics, clinical symptoms, and potential exposures (vaccination status, attending hospital duties, residence/work in hostel) from the cohort. We observed case isolation facilities. We report risk ratios (RR) with 95% confidence intervals (CI). Among the 232 respondents, median age was 22 (range 19–65) years, 90% were students, 47% were female, and none had received Influenza vaccine. There were 47 cases (38 probable, nine confirmed), including seven cases of H1N1pdm09. Cases were reported between September 21 to October 15, 2022, and none were isolated. Symptoms included fever (98%), headache (68%), and body ache (57%). The index case confirmed as Influenza A/H1N1pdm09 resided in girls’ hostel, developed acute necrotizing encephalopathy, and died. Attending hospital duties (RR = 2.7, 95% CI: 1.7–4.5), and residing in girls hostel [RR 2.1 (95% C.I. 1.2–3.4)] were significantly associated with illness. This was an influenza A (H1N1pdm09) outbreak in September-October 2022 among students and staff of College A. An almost three times increased risk of illness among those reporting hospital contact suggests that the source of infection could be exposure to an influenza patient during hospital duties. We recommend vaccinating trainee medical students ahead of hospital duties and early isolation of cases to prevent future outbreaks.