Abstract
IntroductionWe investigated an outbreak of influenza-like illness (ILI) at a boarding school in Eastern Cape Province, South Africa. We aimed to confirm the etiological agent, estimate attack rates and identify risk factors for illness.MethodsWe conducted a retrospective cohort study including senior school boarders (n=308). Students with ILI (cough and fever) were identified through school medical records. We also conducted a questionnaire-based cross-sectional study among senior students including boarders (n=107) and day students (n=45). We collected respiratory specimens for respiratory pathogen testing by real-time polymerase chain reaction from a subset of symptomatic students. We calculated attack rates of medically attended ILI (medILI) and identified factors associated with medILI using logistic regression. We calculated seasonal influenza vaccine effectiveness (VE) against medILI.ResultsInfluenza A (H3N2) virus was detected in 61% (23/38) of specimens. Attack rate for medILI was 13% among boarders (39/308) in the cohort study and 20% in both day students (9/45) and boarders (21/107) in the cross-sectional study. Playing squash was associated with medILI (aOR 5.35, 95% confidence interval [95% CI]: 1.68-17.07). Of the boarders, 19% (57/308) were vaccinated before the outbreak. The adjusted VE against medILI was 18% (aOR 0.82, 95% CI 0.38-1.78). The outbreak led to cancellation of several events and the need for academic remedial sessions.ConclusionWe confirmed an influenza A (H3N2) virus outbreak with a high attack rate. The outbreak affected academic and sports activities. Participation in sports and social gatherings while experiencing ILI should be discouraged to reduce viral transmission and impact on school activities.
Highlights
Influenza-like illness (ILI) and influenza outbreaks commonly occur in schools [1,2], with areas like United Kingdom reporting as many as 658 school respiratory illness outbreaks in one season, with attack rates ranging from 14-45% [3]
On the 14th of July 2016, the resident doctor at a boarding school in the Eastern Cape Province, South Africa, contacted the National Institute for Communicable Diseases (NICD) of the National Health Laboratory Service (NHLS) and reported a large number of students presenting with ILI since the 9th of July, more cases than he had experienced for any influenza season in his time working at the school
The school annually offered the Southern Hemisphere influenza vaccine to consenting students as soon as the vaccine was available in South Africa, which was billed to the student's medical aid
Summary
Influenza-like illness (ILI) and influenza outbreaks commonly occur in schools [1,2], with areas like United Kingdom reporting as many as 658 school respiratory illness outbreaks in one season, with attack rates ranging from 14-45% [3]. Only three outbreaks have been described in peer-reviewed journals This includes an outbreak of influenza A (H3N2) virus in a police residential college in Pretoria in 2003 with an attack rate of 20-47% [4], an outbreak affecting students from several schools in Bophuthatswana in 1978 where the strain was not characterized [5], and an outbreak of influenza A (H2N2) virus in gold miners near Johannesburg in 1958 with an attack rate of 15% [6]. On the 14th of July 2016, the resident doctor at a boarding school in the Eastern Cape Province, South Africa, contacted the National Institute for Communicable Diseases (NICD) of the National Health Laboratory Service (NHLS) and reported a large number of students presenting with ILI since the 9th of July, more cases than he had experienced for any influenza season in his time working at the school. Due to the high number of cases, the disruption of school activities and the unique opportunity to describe an influenza outbreak in a closed population, we conducted an investigation during the 26-29th of July 2016, aimed to confirm the etiological agent, estimate attack rates among students and identify risk factors for illness
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